PREAMBLE (NOT PART OF THE STANDARD)

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END OF PREAMBLE (NOT PART OF THE STANDARD)

Errata

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National Fire Protection Association, National Electrical Code, NFPA 70, and NEC 2011

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Copyright © 2010
National Fire Protection Association®
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Quincy, Massachusetts 02169-7471

NFPA, National Fire Protection Association, National Electrical Code, NFPA 70, and NEC are registered trademarks of the National Fire Protection Association.

IMPORTANT NOTICES AND DISCLAIMERS CONCERNING NFPA® DOCUMENTS

Notice and Disclaimer of Liability Concerning the Use of NFPA Documents

NFPA® codes, standards, recommended practices, and guides (“NFPA Documents”), of which the document contained herein is one, are developed through a consensus standards development process approved by the American National Standards Institute. This process brings together volunteers representing varied viewpoints and interests to achieve consensus on fire and other safety issues. While the NFPA administers the process and establishes rules to promote fairness in the development of consensus, it does not independently test, evaluate, or verify the accuracy of any information or the soundness of any judgments contained in NFPA Documents.

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ISBN: 978-087765914-3 (SB Print)
ISBN: 978-087765915-0 (LL Print)
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Updating of NFPA Documents

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Copyright © 2010, National Fire Protection Association®. All Rights Reserved

NFPA 70®

National Electrical Code®

2011 Edition

This edition of NFPA 70, National Electrical Code, was prepared by the National Electrical Code Committee and acted on by NFPA at its June Association Technical Meeting held June 7–10, 2010, in Las Vegas, NV. It was issued by the Standards Council on August 5, 2010, with an effective date of August 25, 2010, and supersedes all previous editions.

This edition of NFPA 70 was approved as an American National Standard on August 25, 2010.

History and Development of the National Electrical Code®

The National Fire Protection Association has acted as sponsor of the National Electrical Code since 1911. The original Code document was developed in 1897 as a result of the united efforts of various insurance, electrical, architectural, and allied interests.

In accordance with the provisions of the NFPA Regulations Governing Committee Projects, a National Electrical Code Committee Report on Proposals containing proposed amendments to the 2008 National Electrical Code was published by NFPA in July 2009. This report recorded the actions of the various Code-Making Panels and the Correlating Committee of the National Electrical Code Committee on each proposal that had been made to revise the 2008 Code. The report was circulated to all members of the National Electrical Code Committee and was made available to other interested NFPA members and to the public for review and comment. Following the close of the public comment period, the Code-Making Panels met, acted on each comment, and reported their action to the Correlating Committee. NFPA published the National Electrical Code Committee Report on Comments in March 2010, which recorded the actions of the Code-Making Panels and the Correlating Committee on each public comment to the National Electrical Code Committee Report on Proposals. The National Electrical Code Committee Report on Proposals and the National Electrical Code Committee Report on Comments were presented to the 2010 June Association Technical Meeting for adoption.

NFPA has an Electrical Section that provides particular opportunity for NFPA members interested in electrical safety to become better informed and to contribute to the development of the National Electrical Code and other NFPA electrical standards. At the Electrical Section Codes and Standards Review Session held at the 2010 NFPA Conference and Expo, Section members had opportunity to discuss and review the report of the National Electrical Code Committee prior to the adoption of this edition of the Code by the Association at its 2010 June Technical Session.

This 52nd edition supersedes all other previous editions, supplements, and printings dated 1897, 1899, 1901, 1903, 1904, 1905, 1907, 1909, 1911, 1913, 1915, 1918, 1920, 1923, 1925, 1926, 1928, 1930, 1931, 1933, 1935, 1937, 1940, 1942, 1943, 1947, 1949, 1951, 1953, 1954, 1955, 1956, 1957, 1958, 1959, 1962, 1965, 1968, 1971, 1975, 1978, 1981, 1984, 1987, 1990, 1993, 1996, 1999, 2002, 2005, and 2008.

This Code is purely advisory as far as NFPA is concerned. It is made available for a wide variety of both public and private uses in the interest of life and property protection. These include both use in law and for regulatory purposes, and use in private self-regulation and standardization activities such as insurance underwriting, building and facilities construction and management, and product testing and certification.

70-1

Contents

ARTICLE
90 Introduction 70–22
Chapter 1 General
100 Definitions 70–26
  I. General 70–26
  II. Over 600 Volts, Nominal 70–33
110 Requirements for Electrical Installations 70–34
  I. General 70–34
  II. 600 Volts, Nominal, or Less 70–37
  III. Over 600 Volts, Nominal 70–40
  IV. Tunnel Installations over 600 Volts, Nominal 70–43
  V. Manholes and Other Electrical Enclosures Intended for Personnel Entry, All Voltages 70–44
Chapter 2 Wiring and Protection
200 Use and Identification of Grounded Conductors 70–46
210 Branch Circuits 70–48
  I. General Provisions 70–48
  II. Branch-Circuit Ratings 70–52
  III. Required Outlets 70–55
215 Feeders 70–59
220 Branch-Circuit, Feeder, and Service Calculations 70–61
  I. General 70–61
  II. Branch-Circuit Load Calculations 70–61
  III. Feeder and Service Load Calculations 70–64
  IV. Optional Feeder and Service Load Calculations 70–67
  V. Farm Load Calculations 70–70
225 Outside Branch Circuits and Feeders 70–71
  I. General 70–71
  II. Buildings or Other Structures Supplied by a Feeder(s) or Branch Circuit(s) 70–74
  III. Over 600 Volts 70–76
230 Services 70–78
  I. General 70–78
  II. Overhead Service Conductors 70–79
  III. Underground Service Conductors 70–81
  IV. Service-Entrance Conductors 70–81
  V. Service Equipment — General 70–84
  VI. Service Equipment — Disconnecting Means 70–84
  VII. Service Equipment — Overcurrent Protection 70–86
  VIII. Services Exceeding 600 Volts, Nominal 70–87
240 Overcurrent Protection 70–88
  I. General 70–88
  II. Location 70–92
  III. Enclosures 70–95
  IV. Disconnecting and Guarding 70–96
  V. Plug Fuses, Fuseholders, and Adapters 70–96
  VI. Cartridge Fuses and Fuseholders 70–97
  VII. Circuit Breakers 70–97
  VIII. Supervised Industrial Installations 70–98
  IX. Overcurrent Protection Over 600 Volts, Nominal 70–100
250 Grounding and Bonding 70–100
  I. General 70–100
  II. System Grounding 70–103
  III. Grounding Electrode System and Grounding Electrode Conductor 70–111
  IV. Enclosure, Raceway, and Service Cable Connections 70–116
  V. Bonding 70–117
  VI. Equipment Grounding and Equipment Grounding Conductors 70–120
  VII. Methods of Equipment Grounding 70–125
  VIII. Direct-Current Systems 70–128
  IX. Instruments, Meters, and Relays 70–129
  X. Grounding of Systems and Circuits of over 1 kV 70–129
280 Surge Arresters, Over 1 kV 70–131
  I. General 70–131
  II. Installation 70–132
  III. Connecting Surge Arresters 70–132
285 Surge-Protective Devices (SPDs), 1 kV or Less 70–133
  I. General 70–133
  II. Installation 70–133
  III. Connecting SPDs 70–133
Chapter 3 Wiring Methods and Materials
300 Wiring Methods 70–135
  I. General Requirements 70–135
  II. Requirements for over 600 Volts, Nominal 70–145
310 Conductors for General Wiring 70–147
  I. General 70–147
  II. Installation 70–147
  III. Construction Specifications 70–168
312 Cabinets, Cutout Boxes, and Meter Socket Enclosures 70–173
  I. Installation 70–174
  II. Construction Specifications 70–175
314 Outlet, Device, Pull, and Junction Boxes; Conduit Bodies; Fittings; and Handhole Enclosures 70–177
  I. Scope and General 70–177
  II. Installation 70–177
  III. Construction Specifications 70–184
  IV. Pull and Junction Boxes, Conduit Bodies, and Handhole Enclosures for Use on Systems over 600 Volts, Nominal 70–185 70-2
320 Armored Cable: Type AC 70–186
  I. General 70–186
  II. Installation 70–186
  III. Construction Specifications 70–187
322 Flat Cable Assemblies: Type FC 70–187
  I. General 70–187
  II. Installation 70–188
  III. Construction 70–188
324 Flat Conductor Cable: Type FCC 70–189
  I. General 70–189
  II. Installation 70–189
  III. Construction 70–190
326 Integrated Gas Spacer Cable: Type IGS 70–191
  I. General 70–191
  II. Installation 70–191
  III. Construction Specifications 70–191
328 Medium Voltage Cable: Type MV 70–192
  I. General 70–192
  II. Installation 70–192
  III. Construction Specifications 70–192
330 Metal-Clad Cable: Type MC 70–192
  I. General 70–192
  II. Installation 70–193
  III. Construction Specifications 70–194
332 Mineral-Insulated, Metal-Sheathed Cable: Type MI 70–194
  I. General 70–194
  II. Installation 70–195
  III. Construction Specifications 70–196
334 Nonmetallic-Sheathed Cable: Types NM, NMC, and NMS 70–196
  I. General 70–196
  II. Installation 70–196
  III. Construction Specifications 70–198
336 Power and Control Tray Cable: Type TC 70–198
  I. General 70–198
  II. Installation 70–199
  III. Construction Specifications 70–199
338 Service-Entrance Cable: Types SE and USE 70–200
  I. General 70–200
  II. Installation 70–200
  III. Construction 70–201
340 Underground Feeder and Branch-Circuit Cable: Type UF 70–201
  I. General 70–201
  II. Installation 70–201
  III. Construction Specifications 70–202
342 Intermediate Metal Conduit: Type IMC 70–202
  I. General 70–202
  II. Installation 70–202
  III. Construction Specifications 70–203
344 Rigid Metal Conduit: Type RMC 70–203
  I. General 70–203
  II. Installation 70–203
  III. Construction Specifications 70–205
348 Flexible Metal Conduit: Type FMC 70–205
  I. General 70–205
  II. Installation 70–205
350 Liquidtight Flexible Metal Conduit: Type LFMC 70–207
  I. General 70–207
  II. Installation 70–207
  III. Construction Specifications 70–208
352 Rigid Polyvinyl Chloride Conduit: Type PVC 70–208
  I. General 70–208
  II. Installation 70–208
  III. Construction Specifications 70–210
353 High Density Polyethylene Conduit: Type HDPE Conduit 70–211
  I. General 70–211
  II. Installation 70–211
  III. Construction Specifications 70–212
354 Nonmetallic Underground Conduit with Conductors: Type NUCC 70–212
  I. General 70–212
  II. Installation 70–212
  III. Construction Specifications 70–213
355 Reinforced Thermosetting Resin Conduit: Type RTRC 70–213
  I. General. 70–213
  II. Installation 70–214
  III. Construction Specifications 70–216
356 Liquidtight Flexible Nonmetallic Conduit: Type LFNC 70–216
  I. General 70–216
  II. Installation 70–216
  III. Construction Specifications 70–217
358 Electrical Metallic Tubing: Type EMT 70–218
  I. General 70–218
  II. Installation 70–218
  III. Construction Specifications 70–219
360 Flexible Metallic Tubing: Type FMT 70–219
  I. General 70–219
  II. Installation 70–219
  III. Construction Specifications 70–220
362 Electrical Nonmetallic Tubing: Type ENT 70–220
  I. General 70–220
  II. Installation 70–220
  III. Construction Specifications 70–222
366 Auxiliary Gutters 70–222
  I. General 70–222
  II. Installation 70–222
  III. Construction Specifications 70–224 70-3
368 Busways 70–224
  I. General Requirements 70–224
  II. Installation 70–224
  III. Construction 70–226
  IV. Requirements for Over 600 Volts, Nominal 70–226
370 Cablebus 70–227
372 Cellular Concrete Floor Raceways 70–228
374 Cellular Metal Floor Raceways 70–229
  I. Installation 70–229
  II. Construction Specifications 70–229
376 Metal Wireways 70–230
  I. General 70–230
  II. Installation 70–230
  III. Construction Specifications 70–231
378 Nonmetallic Wireways 70–231
  I. General 70–231
  II. Installation 70–231
  III. Construction Specifications 70–232
380 Multioutlet Assembly 70–232
  I. General 70–232
  II. Installation 70–232
382 Nonmetallic Extensions 70–233
  I. General 70–233
  II. Installation 70–233
  III. Construction Specifications (Concealable Nonmetallic Extensions Only) 70–234
384 Strut-Type Channel Raceway 70–235
  I. General 70–235
  II. Installation 70–235
  III. Construction Specifications 70–236
386 Surface Metal Raceways 70–236
  I. General 70–236
  II. Installation 70–236
  III. Construction Specifications 70–237
388 Surface Nonmetallic Raceways 70–237
  I. General 70–237
  II. Installation 70–237
  III. Construction Specifications 70–238
390 Underfloor Raceways 70–238
392 Cable Trays 70–239
  I. General 70–239
  II. Installation 70–239
  III. Construction Specifications 70–246
394 Concealed Knob-and-Tube Wiring 70–246
  I. General 70–246
  II. Installation 70–246
  III. Construction Specifications 70–247
396 Messenger-Supported Wiring 70–247
  I. General 70–247
  II. Installation 70–248
398 Open Wiring on Insulators 70–248
  I. General 70–248
  II. Installation 70–248
  III. Construction Specifications 70–250
399 Outdoor Overhead Conductors over 600 Volts 70–250
Chapter 4 Equipment for General Use
400 Flexible Cords and Cables 70–251
  I. General 70–251
  II. Construction Specifications 70–260
  III. Portable Cables Over 600 Volts, Nominal 70–261
402 Fixture Wires 70–262
404 Switches 70–266
  I. Installation 70–266
  II. Construction Specifications 70–270
406 Receptacles, Cord Connectors, and Attachment Plugs (Caps) 70–270
408 Switchboards and Panelboards 70–274
  I. General 70–274
  II. Switchboards 70–275
  III. Panelboards 70–276
  IV. Construction Specifications 70–277
409 Industrial Control Panels 70–278
  I. General 70–278
  II. Installation 70–278
  III. Construction Specifications 70–279
410 Luminaires, Lampholders, and Lamps 70–280
  I. General 70–280
  II. Luminaire Locations 70–281
  III. Provisions at Luminaire Outlet Boxes, Canopies, and Pans 70–282
  IV. Luminaire Supports 70–282
  V. Grounding 70–283
  VI. Wiring of Luminaires 70–283
  VII. Construction of Luminaires 70–285
  VIII. Installation of Lampholders 70–285
  IX. Lamps and Auxiliary Equipment 70–285
  X. Special Provisions for Flush and Recessed Luminaires 70–286
  XI. Construction of Flush and Recessed Luminaires 70–286
  XII. Special Provisions for Electric-Discharge Lighting Systems of 1000 Volts or Less 70–286
  XIII. Special Provisions for Electric-Discharge Lighting Systems of More Than 1000 Volts 70–288
  XIV. Lighting Track 70–289
  XV. Decorative Lighting and Similar Accessories 70–289
411 Lighting Systems Operating at 30 Volts or Less 70–289
422 Appliances 70–290
  I. General 70–290 70-4
  II. Installation 70–290
  III. Disconnecting Means 70–293
  IV. Construction 70–294
  V. Marking 70–295
424 Fixed Electric Space-Heating Equipment 70–295
  I. General 70–295
  II. Installation 70–296
  III. Control and Protection of Fixed Electric Space-Heating Equipment 70–296
  IV. Marking of Heating Equipment 70–298
  V. Electric Space-Heating Cables 70–298
  VI. Duct Heaters 70–300
  VII. Resistance-Type Boilers 70–300
  VIII. Electrode-Type Boilers 70–301
  IX. Electric Radiant Heating Panels and Heating Panel Sets 70–302
426 Fixed Outdoor Electric Deicing and Snow-Melting Equipment 70–304
  I. General 70–304
  II. Installation 70–305
  III. Resistance Heating Elements 70–305
  IV. Impedance Heating 70–306
  V. Skin-Effect Heating 70–306
  VI. Control and Protection 70–307
427 Fixed Electric Heating Equipment for Pipelines and Vessels 70–307
  I. General 70–307
  II. Installation 70–308
  III. Resistance Heating Elements 70–308
  IV. Impedance Heating 70–309
  V. Induction Heating 70–309
  VI. Skin-Effect Heating 70–309
  VII. Control and Protection 70–309
430 Motors, Motor Circuits, and Controllers 70–310
  I. General 70–310
  II. Motor Circuit Conductors 70–316
  III. Motor and Branch-Circuit Overload Protection 70–319
  IV. Motor Branch-Circuit Short-Circuit and Ground-Fault Protection 70–322
  V. Motor Feeder Short-Circuit and Ground-Fault Protection 70–325
  VI. Motor Control Circuits 70–326
  VII. Motor Controllers 70–327
  VIII. Motor Control Centers 70–329
  IX. Disconnecting Means 70–330
  X. Adjustable-Speed Drive Systems 70–333
  XI. Over 600 Volts, Nominal 70–334
  XII. Protection of Live Parts — All Voltages 70–335
  XIII. Grounding — All Voltages 70–335
  XIV. Tables 70–336
440 Air-Conditioning and Refrigerating Equipment 70–340
  I. General 70–340
  II. Disconnecting Means 70–342
  III. Branch-Circuit Short-Circuit and Ground-Fault Protection 70–343
  IV. Branch-Circuit Conductors 70–344
  V. Controllers for Motor-Compressors 70–344
  VI. Motor-Compressor and Branch-Circuit Overload Protection 70–345
  VII. Provisions for Room Air Conditioners 70–346
445 Generators 70–347
450 Transformers and Transformer Vaults (Including Secondary Ties) 70–348
  I. General Provisions 70–348
  II. Specific Provisions Applicable to Different Types of Transformers 70–352
  III. Transformer Vaults 70–354
455 Phase Converters 70–355
  I. General 70–355
  II. Specific Provisions Applicable to Different Types of Phase Converters 70–356
460 Capacitors 70–357
  I. 600 Volts, Nominal, and Under 70–357
  II. Over 600 Volts, Nominal 70–358
470 Resistors and Reactors 70–358
  I. 600 Volts, Nominal, and Under 70–358
  II. Over 600 Volts, Nominal 70–359
480 Storage Batteries 70–359
490 Equipment, Over 600 Volts, Nominal 70–360
  I. General 70–360
  II. Equipment — Specific Provisions 70–361
  III. Equipment — Metal-Enclosed Power Switchgear and Industrial Control Assemblies 70–363
  IV. Mobile and Portable Equipment 70–365
  V. Electrode-Type Boilers 70–366
Chapter 5 Special Occupancies
500 Hazardous (Classified) Locations, Classes I, II, and III, Divisions 1 and 2 70–367
501 Class I Locations 70–376
  I. General 70–376
  II. Wiring 70–376
  III. Equipment 70–381
502 Class II Locations 70–386
  I. General 70–386
  II. Wiring 70–386
  III. Equipment 70–388
503 Class III Locations 70–391
  I. General 70–391
  II. Wiring 70–391
  III. Equipment 70–392
504 Intrinsically Safe Systems 70–394
505 Zone 0, 1, and 2 Locations 70–397
506 Zone 20, 21, and 22 Locations for Combustible Dusts or Ignitible Fibers/Flyings 70–412
510 Hazardous (Classified) Locations — Specific 70–419 70-5
511 Commercial Garages, Repair and Storage 70–419
513 Aircraft Hangars 70–422
514 Motor Fuel Dispensing Facilities 70–425
515 Bulk Storage Plants 70–429
516 Spray Application, Dipping, and Coating Processes 70–434
517 Health Care Facilities 70–440
  I. General 70–440
  II. Wiring and Protection 70–442
  III. Essential Electrical System 70–445
  IV. Inhalation Anesthetizing Locations 70–452
  V. X-Ray Installations 70–455
  VI. Communications, Signaling Systems, Data Systems,
Fire Alarm Systems, and Systems Less Than 120 Volts, Nominal
70–456
  VII. Isolated Power Systems 70–457
518 Assembly Occupancies 70–458
520 Theaters, Audience Areas of Motion Picture and Television Studios, Performance Areas, and Similar Locations 70–459
  I. General 70–159
  II. Fixed Stage Switchboards 70–461
  III. Fixed Stage Equipment Other Than Switchboards 70–462
  IV. Portable Switchboards on Stage 70–463
  V. Portable Stage Equipment Other Than Switchboards 70–466
  VI. Dressing Rooms 70–468
  VII. Grounding 70–468
522 Control Systems for Permanent Amusement Attractions 70–468
  I. General 70–468
  II. Control Circuits 70–468
  III. Control Circuit Wiring Methods 70–469
525 Carnivals, Circuses, Fairs, and Similar Events 70–470
  I. General Requirements 70–470
  II. Power Sources 70–470
  III. Wiring Methods 70–471
  IV. Grounding and Bonding 70–472
530 Motion Picture and Television Studios and Similar Locations 70–472
  I. General 70–472
  II. Stage or Set 70–473
  III. Dressing Rooms 70–475
  IV. Viewing, Cutting, and Patching Tables 70–475
  V. Cellulose Nitrate Film Storage Vaults 70–475
  VI. Substations 70–475
540 Motion Picture Projection Rooms 70–476
  I. General 70–476
  II. Equipment and Projectors of the Professional Type 70–476
  III. Nonprofessional Projectors 70–477
  IV. Audio Signal Processing, Amplification, and Reproduction Equipment 70–477
545 Manufactured Buildings 70–477
547 Agricultural Buildings 70–478
550 Mobile Homes, Manufactured Homes, and Mobile Home Parks 70–481
  I. General 70–481
  II. Mobile and Manufactured Homes 70–482
  III. Services and Feeders 70–489
551 Recreational Vehicles and Recreational Vehicle Parks 70–490
  I. General 70–490
  II. Combination Electrical Systems 70–491
  III. Other Power Sources 70–492
  IV. Nominal 120-Volt or 120/240-Volt Systems 70–493
  V. Factory Tests 70–500
  VI. Recreational Vehicle Parks 70–500
552 Park Trailers 70–503
  I. General 70–503
  II. Low-Voltage Systems 70–503
  III. Combination Electrical Systems 70–504
  IV. Nominal 120-Volt or 120/240-Volt Systems 70–505
  V. Factory Tests 70–511
553 Floating Buildings 70–512
  I. General 70–512
  II. Services and Feeders 70–512
  III. Grounding 70–512
555 Marinas and Boatyards 70–513
590 Temporary Installations 70–516
Chapter 6 Special Equipment
600 Electric Signs and Outline Lighting 70–519
  I. General 70–519
  II. Field-Installed Skeleton Tubing, Outline Lighting, and Secondary Wiring 70–523
604 Manufactured Wiring Systems 70–525
605 Office Furnishings (Consisting of Lighting Accessories and Wired Partitions) 70–526
610 Cranes and Hoists 70–527
  I. General 70–527
  II. Wiring 70–527
  III. Contact Conductors 70–530
  IV. Disconnecting Means 70–531
  V. Overcurrent Protection 70–531
  VI. Control 70–532
  VII. Grounding 70–532
620 Elevators, Dumbwaiters, Escalators, Moving Walks, Platform Lifts, and Stairway Chairlifts 70–532
  I. General 70–532 70-6
  II. Conductors 70–534
  III. Wiring 70–536
  IV. Installation of Conductors 70–538
  V. Traveling Cables 70–539
  VI. Disconnecting Means and Control 70–540
  VII. Overcurrent Protection 70–542
  VIII. Machine Rooms, Control Rooms, Machinery Spaces, and Control Spaces 70–542
  IX. Grounding 70–543
  X. Emergency and Standby Power Systems 70–543
625 Electric Vehicle Charging System 70–543
  I. General 70–543
  II. Wiring Methods 70–544
  III. Equipment Construction 70–544
  IV. Control and Protection 70–545
  V. Electric Vehicle Supply Equipment Locations 70–545
626 Electrified Truck Parking Spaces 70–547
  I. General 70–547
  II. Electrified Truck Parking Space Electrical Wiring Systems 70–548
  III. Electrified Truck Parking Space Supply Equipment 70–549
  IV. Transport Refrigerated Units (TRUs) 70–551
630 Electric Welders 70–552
  I. General 70–552
  II. Are Welders 70–552
  III. Resistance Welders 70–553
  IV. Welding Cable 70–554
640 Audio Signal Processing, Amplification, and Reproduction Equipment 70–554
  I. General 70–554
  II. Permanent Audio System Installations 70–557
  III. Portable and Temporary Audio System Installations 70–558
645 Information Technology Equipment 70–559
647 Sensitive Electronic Equipment 70–563
650 Pipe Organs 70–564
660 X-Ray Equipment 70–565
  I. General 70–565
  II. Control 70–566
  III. Transformers and Capacitors 70–566
  IV. Guarding and Grounding 70–566
665 Induction and Dielectric Heating Equipment 70–567
  I. General 70–567
  II. Guarding, Grounding, and Labeling 70–568
668 Electrolytic Cells 70–568
669 Electroplating 70–571
670 Industrial Machinery 70–572
675 Electrically Driven or Controlled Irrigation Machines 70–573
  I. General 70–573
  II. Center Pivot Irrigation Machines 70–575
680 Swimming Pools, Fountains, and Similar Installations 70–575
  I. General 70–575
  II. Permanently Installed Pools 70–579
  III. Storable Pools 70–585
  IV. Spas and Hot Tubs 70–586
  V. Fountains 70–588
  VI. Pools and Tubs for Therapeutic Use 70–589
  VII. Hydromassage Bathtubs 70–590
682 Natural and Artificially Made Bodies of Water 70–590
  I. General 70–590
  II. Installation 70–591
  III. Grounding and Bonding 70–592
685 Integrated Electrical Systems 70–592
  I. General 70–592
  II. Orderly Shutdown 70–593
690 Solar Photovoltaic (PV) Systems 70–593
  I. General 70–593
  II. Circuit Requirements 70–597
  III. Disconnecting Means 70–599
  IV. Wiring Methods 70–601
  V. Grounding 70–603
  VI. Marking 70–604
  VII. Connection to Other Sources 70–605
  VIII. Storage Batteries 70–605
  IX. Systems over 600 Volts 70–607
692 Fuel Cell Systems 70–607
  I. General 70–607
  II. Circuit Requirements 70–608
  III. Disconnecting Means 70–608
  IV. Wiring Methods 70–609
  V. Grounding 70–609
  VI. Marking 70–609
  VII. Connection to Other Circuits 70–609
  VIII. Outputs Over 600 Volts 70–609
694 Small Wind Electric Systems 70–610
  I. General 70–610
  II. Circuit Requirements 70–611
  III. Disconnecting Means 70–612
  IV. Wiring Methods 70–613
  V. Grounding 70–613
  VI. Marking 70–614
  VII. Connection to Other Sources 70–614
  VIII. Storage Batteries 70–614
  IX. Systems over 600 Volts 70–616
695 Fire Pumps 70–616
Chapter 7 Special Conditions
700 Emergency Systems 70–622
  I. General 70–622
  II. Circuit Wiring 70–623
  III. Sources of Power 70–624
  IV. Emergency System Circuits for Lighting and Power 70–626
  V. Control — Emergency Lighting Circuits 70–626 70-7
  VI. Overcurrent Protection 70–627
701 Legally Required Standby Systems 70–627
  I. General 70–627
  II. Circuit Wiring 70–628
  III. Sources of Power 70–628
  IV. Overcurrent Protection 70–630
702 Optional Standby Systems 70–630
  I. General 70–630
  II. Wiring 70–631
705 Interconnected Electric Power Production Sources 70–631
  I. General 70–631
  II. Utility-Interactive Inverters 70–634
  III. Generators 70–635
708 Critical Operations Power Systems (COPS) 70–635
  I. General 70–636
  II. Circuit Wiring and Equipment 70–637
  III. Power Sources and Connection 70–638
  IV. Overcurrent Protection 70–640
  V. System Performance and Analysis 70–640
720 Circuits and Equipment Operating at Less Than 50 Volts 70–640
725 Class 1, Class 2, and Class 3 Remote-Control, Signaling, and Power-Limited Circuits 70–641
  I. General 70–641
  II. Class 1 Circuits 70–642
  III. Class 2 and Class 3 Circuits 70–644
  IV. Listing Requirements 70–648
727 Instrumentation Tray Cable: Type ITC 70–650
760 Fire Alarm Systems 70–651
  I. General 70–651
  II. Non-Power-Limited Fire Alarm (NPLFA) Circuits 70–652
  III. Power-Limited Fire Alarm (PLFA) Circuits 70–654
  IV. Listing Requirements 70–657
770 Optical Fiber Cables and Raceways 70–660
  I. General 70–660
  II. Cables Outside and Entering Buildings 70–661
  III. Protection 70–661
  IV. Grounding Methods 70–661
  V. Installation Methods Within Buildings 70–663
  VI. Listing Requirements 70–666
Chapter 8 Communications Systems
800 Communications Circuits 70–669
  I. General 70–669
  II. Wires and Cables Outside and Entering Buildings 70–670
  III. Protection 70–672
  IV. Grounding Methods 70–673
  V. Installation Methods Within Buildings 70–675
  VI. Listing Requirements 70–680
810 Radio and Television Equipment 70–682
  I. General 70–682
  II. Receiving Equipment — Antenna Systems 70–682
  III. Amateur and Citizen Band Transmitting and Receiving Stations — Antenna Systems 70–685
  IV. Interior Installation — Transmitting Stations 70–686
820 Community Antenna Television and Radio Distribution Systems 70–686
  I. General 70–686
  II. Coaxial Cables Outside and Entering Buildings 70–687
  III. Protection 70–688
  IV. Grounding Methods 70–689
  V. Installation Methods Within Buildings 70–690
  VI. Listing Requirements 70–693
830 Network-Powered Broadband Communications Systems 70–695
  I. General 70–695
  II. Cables Outside and Entering Buildings 70–697
  III. Protection 70–699
  IV. Grounding Methods 70–701
  V. Installation Methods Within Buildings 70–702
  VI. Listing Requirements 70–705
840 Premises-Powered Broadband Communications Systems 70–707
  I. General 70–707
  II. Cables Outside and Entering Buildings 70–708
  III. Protection 70–709
  IV. Grounding Methods 70–709
  V. Installation Methods Within Buildings 70–709
  VI. Listing Requirements 70–710
Chapter 9 Tables
TABLES
1 Percent of Cross Section of Conduit and Tubing for Conductors 70–711
2 Radius of Conduit and Tubing Bends 70–711
4 Dimensions and Percent Area of Conduit and Tubing (Areas of Conduit or Tubing for
the Combinations of Wires Permitted in Table 1, Chapter 9)
70–712
5 Dimensions of Insulated Conductors and Fixture Wires 70–716
5A   Compact Copper and Aluminum Building Wire Nominal Dimensions* and Areas 70–720
8 Conductor Properties 70–721
9 Alternating-Current Resistance and Reactance for 600-Volt Cables, 3-Phase, 60 Hz,
75°C (167°F) — Three Single Conductors in Conduit
70–722
10 Conductor Stranding 70–723 70-8
11(A) Class 2 and Class 3 Alternating-Current Power Source Limitations 70–724
11(B) Class 2 and Class 3 Direct-Current Power Source Limitations 70–725
12(A) PLFA Alternating-Current Power Source Limitations 70–726
12(B) PLFA Direct-Current Power Source Limitations 70–726
  Informative Annex A Product Safety Standards 70–727
  Informative Annex B Application Information for Ampacity Calculation 70–730
  Informative Annex C Conduit and Tubing Fill Tables for Conductors and Fixture Wires of the Same Size 70–744
  Informative Annex D Examples 70–804
  Informative Annex E Types of Construction 70–814
  Informative Annex F Availability and Reliability for Critical
Operations Power Systems; and Development and Implementation of Functional Performance
Tests (FPTs) for Critical Operations Power Systems
70–816
  Informative Annex G Supervisory Control and Data Acquisition (SCADA) 70–819
  Informative Annex H Administration and Enforcement 70–821
  Informative Annex I Recommended Tightening Torque Tables from UL Standard 486A-B 70–828
  Index 70–830
70-9

NATIONAL ELECTRICAL CODE COMMITTEE

These lists represent the membership at the time the Committee was balloted on the final text of this edition. Since that time, changes in the membership may have occurred. A key to classifications is found at the back of this document.

Technical Correlating Committee

James W. Carpenter, Chair
International Association of Electrical Inspectors, NC [E]
Rep. International Association of Electrical Inspectors

Mark W. Earley, Secretary
National Fire Protection Association, MA
(nonvoting)

Jean A. O’Connor, Recording Secretary
National Fire Protection Association, MA
(nonvoting)

James E. Brunssen, Telcordia, NJ [UT]
    Rep. Alliance for Telecommunications Industry Solutions

Merton W. Bunker, Jr., US Department of State, VA [U]
    (VL to Document: 110, Document: 111, Document: 70,
    Document: 70B, Document: 70E, Document: 79,
    Document: 790, Document: 791)

James M. Daly, General Cable, NJ [M]
    Rep. National Electrical Manufacturers Association

William R. Drake, Actuant Electrical, CA [M]

Stanley J. Folz, Morse Electric Company, NV [IM]
    Rep. National Electrical Contractors Association

Palmer L. Hickman, National Joint Apprentice & Training Committee, MD [L]
    Rep. International Brotherhood of Electrical Workers

David L. Hittinger, Independent Electrical Contractors of Greater Cincinnati, OH [IM]
    Rep. Independent Electrical Contractors, Inc.

John R. Kovacik, Underwriters Laboratories Inc., IL [RT]

Neil F. LaBrake, Jr., National Grid, NY [UT]
    Rep. Electric Light & Power Group/EEI

Danny Liggett, DuPont Engineering, Inc., TX [U]
    Rep. American Chemistry Council

Alternates

Thomas L. Adams, Engineering Consultant, IL [UT]
    (Alt. to Neil F. LaBrake, Jr.)
    Rep. Electric Light & Power Group/EEI

Lawrence S. Ayer, Biz Com Electric, Inc., OH [IM]
    (Alt. to David L. Hittinger)
    Rep. Independent Electrical Contractors, Inc.

Larry D. Cogburn, Cogburn Bros, Inc., FL [IM]
    (Alt. to Stanley J. Folz)
    Rep. National Electrical Contractors Association

James T. Dollard, Jr., IBEW Local Union 98, PA [L]
    (Alt. to Palmer L. Hickman)
    Rep. International Brotherhood of Electrical Workers

Ernest J. Gallo, Telcordia Technologies, Inc., NJ [UT]
    (Alt. to James E. Brunssen)
    Rep. Alliance for Telecommunications Industry Solutions

Daniel J. Kissane, Legrand/Pass & Seymour, NY [M]
    (Alt. to James M. Daly)
    Rep. National Electrical Manufacturers Association

Michael E. McNeil, FMC Bio Polymer, ME [U]
    (Alt. to Danny Liggett)
    Rep. American Chemistry Council

Mark C. Ode, Underwriters Laboratories Inc., AZ [RT]
    (Alt. to John R. Kovacik)

Richard P. Owen, Oakdale, MN [E]
    (Alt. to James W. Carpenter)
    Rep. International Association of Electrical Inspectors

Nonvoting

Richard G. Biermann, Biermann Electric Company, Inc., IA [IM]
    (Member Emeritus)

David Mascarenhas, Canadian Standards Association, Canada [RT]

D. Harold Ware, Libra Electric Company, OK [IM]

Mark W. Earley, NFPA Staff Liaison

Committee Scope: This Committee shall have primary responsibility for documents on minimizing the risk of electricity as a source of electric shock and as a potential ignition source of fires and explosions. It shall also be responsible for text to minimize the propagation of fire and explosions due to electrical installations.

CODE-MAKING PANEL NO. 1
Articles 90, 100, 110, Chapter 9, Table 10, Annex A, Annex H, Annex I

Gil Moniz, Chair
National Electrical Manufacturers Association, MA [M]

Michael A. Anthony, University of Michigan, MI [U]
    Rep. Association of Higher Education Facilities Officers

Louis A. Barrios, Shell Global Solutions, TX [U]
    Rep. American Chemistry Council

Kenneth P. Boyce, Underwriters Laboratories Inc., IL [RT]

William T. Fiske, Intertek Testing Services, NY [RT]

H. Landis Floyd, The DuPont Company, DE [U]
    Rep. Institute of Electrical & Electronics Engineers, Inc.

Palmer L. Hickman, National Joint Apprentice & Training Committee, MD [L]
    Rep. International Brotherhood of Electrical Workers

David L. Hittinger, Independent Electrical Contractors of Greater Cincinnati, OH [IM]
    Rep. Independent Electrical Contractors, Inc.

Neil F. LaBrake, Jr., National Grid, NY [UT]
    Rep. Electric Light & Power Group/EEI

Randall R. McCarver, Telcordia Technologies, Inc., NJ [U]
    Rep. Alliance for Telecommunications Industry Solutions

Harry J. Sassaman, Forest Electric Corporation, NJ [IM]
    Rep. National Electrical Contractors Association

70-10

Alternates

Thomas L. Adams, Engineering Consultant, IL [UT]
    (Alt. to Neil F. LaBrake, Jr.)
    Rep. Electric Light & Power Group/EEI

Joseph F. Andre, National Electrical Manufacturers Association, WA [M]
    (Alt. to Gil Moniz)
    Rep. National Electrical Manufacturers Association

Mark Christian, National Joint Apprentice & Training Committee, MD [L]
    (Alt. to Palmer L. Hickman)
    Rep. International Brotherhood of Electrical Workers

Benjamin F. Dunford, Ben Dunford Electric Company Inc., TN [IM]
    (Alt. to David L. Hittinger)
    Rep. Independent Electrical Contractors, Inc.

Ernest J. Gallo, Telcordia Technologies, Inc., NJ [U]
    (Alt. to Randall R. McCarver)
    Rep. Alliance for Telecommunications Industry Solutions

Thomas R. Lichtenstein, Underwriters Laboratories Inc., IL [RT]
    (Alt. to Kenneth P. Boyce)

Donald H. McCullough, II, Washington Savannah River Company, SC [U]
    (Alt. to H. Landis Floyd)
    Rep. Institute of Electrical & Electronics Engineers, Inc.

Susan Newman Scearce, State of Tennessee, TN [E]
    (Voting Alt. to IAEI Rep.)
    Rep. International Association of Electrical Inspectors

James F. Pierce, Intertek Testing Services, OR [RT]
    (Alt. to William T. Fiske)

Nonvoting

Ark Tsisserev, City of Vancouver, Canada [SE]
    Rep. CSA/Canadian Electrical Code Committee

CODE-MAKING PANEL NO. 2
Articles 210, 215, 220, Annex D Examples Dl through D6

Raymond W. Weber, Chair
    State of Wisconsin, WI [E]
    Rep. International Association of Electrical Inspectors

Richard W. Becker, Engineered Electrical Systems, Inc., WA [U]
    Rep. Institute of Electrical & Electronics Engineers. Inc.

Charles L. Boynton, The DuPont Company, TX [U]
    Rep. American Chemistry Council

Frank Coluccio, New York City Department of Buildings, NY [E]

Thomas L. Harman, University of Houston-Clear Lake, TX [SE]

Donald M. King, IBEW Local Union 313, DE [L]
    Rep. International Brotherhood of Electrical Workers

Robert L. LaRocca, Underwriters Laboratories Inc., NY [RT]

Steven Orlowski, National Association of Home Builders, DC [U]

Jim Pauley, Square D Company/Schneider Electric, KY [M]
    Rep. National Electrical Manufacturers Association

Ronald L. Purvis, Sharpsburg, GA [UT]
    Rep. Electric Light & Power Group/EEI

Robert G. Wilkinson, IEC Texas Gulf Coast, TX [IM]
    Rep. Independent Electrical Contractors, Inc.

Thomas H. Wood, Cecil B. Wood, Inc., IL [IM]
    Rep. National Electrical Contractors Association

Alternates

Jacob G. Benninger, Cornell University, NY [L]
    (Alt. to Donald M. King)
    Rep. International Brotherhood of Electrical Workers

Lawrence Brown, National Association of Home Builders, DC [U]
    (Alt. to Steven Orlowski)

Paul Crivell, Camp, Dresser, & McKee Inc., WA [U]
    (Alt. to Richard W. Becker)
    Rep. Institute of Electrical & Electronics Engineers, Inc.

David A. Dini, Underwriters Laboratories Inc., IL [RT]
    (Alt. to Robert L. LaRocca)

Daniel J. Kissane, Pass & Seymour/Legrand, NY [M]
    (Alt. to Jim Pauley)
    Rep. National Electrical Manufacturers Association

William Ross McCorcle, American Electric Power, OK [UT]
    (Alt. to Ronald L. Purvis)
    Rep. Electric Light & Power Group/EEI

William J. McGovern, City of Plano, TX [E]
    (Alt. to Raymond W. Weber)
    Rep. International Association of Electrical Inspectors

Stephen V. St. Croix, 1st Electric, Inc., MD [IM]
    (Alt. to Robert G. Wilkinson)
    Rep. Independent Electrical Contractors, Inc.

Nonvoting

William Burr, Canadian Standards Association, Canada [RT]

Douglas A. Lee, US Consumer Product Safety Commission, MD [C]

Andrew M. Trotta, US Consumer Product Safety Commission, MD [C]
    (Alt. to Douglas A. Lee)

CODE-MAKING PANEL NO. 3
Articles 300, 590, 720, 725, 727, 760, Chapter 9, Tables 11(A) and (B), Tables 12(A) and (B)

Paul J. Casparro, Chair
Scranton Electricians JATC, PA [L]
Rep. International Brotherhood of Electrical Workers

Lawrence S. Ayer, Biz Com Electric, Inc., OH [IM]
    Rep. Independent Electrical Contractors, Inc.

Thomas F. Connaughton, Intertek Testing Services, NJ [RT]

Les Easter, Tyco/Allied Tube and Conduit, IL [M]
    Rep. National Electrical Manufacturers Association

Sanford E. Egesdal, Egesdal Associates PLC, MN [M]
    Rep. Automatic Fire Alarm Association, Inc.

Stanley D. Kahn, Tri-City Electric Company, Inc., CA [IM]
    Rep. National Electrical Contractors Association

Ray R. Keden, ERICO, Inc., CA [M]
    Rep. Building Industry Consulting Services International

Juan C. Menendez, Southern California Edison Company, CA [UT]
    Rep. Electric Light & Power Group/EEI

70-11

Richard P. Owen, Oakdale, MN [E]
    Rep. International Association of Electrical Inspectors

Steven J. Owen, Steven J. Owen, Inc., AL [IM]
    Rep. Associated Builders & Contractors

David A. Pace, Olin Corporation, AL [U]
    Rep. American Chemistry Council

Melvin K. Sanders, Things Electrical Co., Inc. (TECo., Inc.), IA [U]
    Rep. Institute of Electrical & Electronics Engineers, Inc.

Mark A. Sepulveda, USA Alarm Systems, Inc., CA [IM]
    Rep. National Burglar & Fire Alarm Association
    (VL to 720, 725, 727, 760)

John E. Sleights, Travelers Insurance Company, CT [I]

Susan L. Stene, Underwriters Laboratories Inc., CA [RT]

Alternates

Richard S. Anderson, RTKL Associates Inc., VA [M]
    (Alt. to Ray R. Keden)
    Rep. Building Industry Consulting Services International

Steven D. Burlison, Progress Energy, FL [UT]
    (Alt. to Juan C. Menendez)
    Rep. Electric Light & Power Group/EEI

Shane M. Clary, Bay Alarm Company, CA [M]
    (Alt. to Sanford E. Egesdal)
    Rep. Automatic Fire Alarm Association, Inc.

Adam D. Corbin, Corbin Electrical Services, Inc., NJ [IM]
    (Alt. to Lawrence S. Ayer)
    Rep. Independent Electrical Contractors, Inc.

Danny Liggett, DuPont Company, TX [U]
    (Alt. to David A. Pace)
    Rep. American Chemistry Council

T. David Mills, Savannah River Nuclear Solutions, LLC, SC [U]
    (Alt. to Melvin K. Sanders)
    Rep. Institute of Electrical & Electronics Engineers, Inc.

Mark C. Ode, Underwriters Laboratories Inc., AZ [RT]
    (Alt. to Susan L. Stene)

Roger S. Passmore, IES Industrial, Inc., SC [IM]
    (Alt. to Steven J. Owen)
    Rep. Associated Builders & Contractors

Marty L. Riesberg, IBEW Local Union 22, MD [L]
    (Alt. to Paul J. Casparro)
    Rep. International Brotherhood of Electrical Workers

George A. Straniero, Tyco/AFC Cable Systems, Inc., NJ [M]
    (Alt. to Les Easter)
    Rep. National Electrical Manufacturers Association

Robert J. Walsh, City of Hayward, CA [E]
    (Alt. to Richard P. Owen)
    Rep. International Association of Electrical Inspectors

Wendell R. Whistler, Intertek Testing Services, OR [RT]
    (Alt. to Thomas F. Connaughton)

Nonvoting

Edward C. Lawry, Oregon, WI [E]
    (Member Emeritus)

CODE-MAKING PANEL NO. 4
Articles 225, 230, 690, 692, 694, 705

Ronald J. Toomer, Chair
Toomer Electrical Company Inc., LA [IM]
Rep. National Electrical Contractors Association

Ward I. Bower, Sandia National Laboratories, NM [U]
    Rep. Solar Energy Industries Association
    (VL to 690, 692, 705)

Robert J. Deaton, The Dow Chemical Company, TX [U]
    Rep. Institute of Electrical & Electronics Engineers, Inc.

Tony Dorta, Intertek Testing Services, CA [RT]

Roger D. McDaniel, Georgia Power Company, GA [UT]
    Rep. Electric Light & Power Group/EEI

James J. Rogers, Towns of Oak Bluffs, Tisbury, West Tisbury, MA [E]
    Rep. International Association of Electrical Inspectors

John A. Sigmund, PPG Industries, Inc., LA [U]
    Rep. American Chemistry Council

Todd W. Stafford, National Joint Apprentice & Training Committee, TN [L]
    Rep. International Brotherhood of Electrical Workers

Robert H. Wills, Intergrid, LLC, NH [U]
    Rep. American Wind Energy Association
    (VL to 690, 692, 705)

John W. Young, Siemens Industry, Inc., GA [M]
    Rep. National Electrical Manufacturers Association

Timothy P. Zgonena, Underwriters Laboratories Inc., IL [RT]

Vincent C. Zinnante, Westpoint Electric Inc., TX [IM]
    Rep. Independent Electrical Contractors, Inc.

Alternates

Paul D. Barnhart, Underwriters Laboratories Inc., NC [RT]
    (Alt. to Timothy P. Zgonena)

Alex Z. Bradley, The DuPont Company, DE [U]
    (Alt. to John A. Sigmund)
    Rep. American Chemistry Council

William F. Brooks, Brooks Engineering, CA [U]
    (Alt. to Ward I. Bower)
    Rep. Solar Energy Industries Association
    (VL to 690, 692, 705)

Thomas E. Buchal, Intertek Testing Services, NY [RT]
    (Alt. to Tony Dorta)

Larry D. Cogburn, Cogburn Bros, Inc., FL [IM]
    (Alt. to Ronald J. Toomer)
    Rep. National Electrical Contractors Association

Brian L. Crise, NIETC, OR [L]
    (Alt. to Todd W. Stafford)
    Rep. International Brotherhood of Electrical Workers

Mark D. Gibbs, B&W Y-12, LLC, TN [U]
    (Alt. to Robert J. Deaton)
    Rep. Institute of Electrical & Electronics Engineers, Inc.

Barry N. Hornberger, PECO Energy Company, PA [UT]
    (Alt. to Roger D. McDaniel)
    Rep. Electric Light & Power Group/EEI

Tim LaLonde, Haskin Electric, Inc., WA [IM]
    (Alt. to Vincent C. Zinnante)
    Rep. Independent Electrical Contractors, Inc.

Philip M. Piqueira, General Electric Company, CT [M]
    (Alt. to John W. Young)
    Rep. National Electrical Manufacturers Association

Robert W. Preus, Abundant Renewable Energy, LLC, OR [U]
    (Alt. to Robert H. Wills)
    Rep. American Wind Energy Association
    (VL to 690, 692, 705)

Glenn A. Soles, Clark County Department of Development Services, NV [E]
    (Alt. to James J. Rogers)
    Rep. International Association of Electrical Inspectors

70-12

CODE-MAKING PANEL NO. 5
Articles 200, 250, 280, 285

Michael J. Johnston, Chair
National Electrical Contractors Association, MD [IM]

Trevor N. Bowmer, Telcordia Technologies, NJ [U]
    Rep. Alliance for Telecommunications Industry Solutions

David Brender, Copper Development Association, Inc., NY [M]
    Rep. Copper Development Association Inc.

Martin J. Brett, Jr., Wheatland Tube Company, DE [M]
    Rep. American Iron and Steel Institute

Paul Dobrowsky, Innovative Technology Services, NY [U]
    Rep. American Chemistry Council

Dan Hammel, IBEW Local Union 704, IA [L]
    Rep. International Brotherhood of Electrical Workers

G. Scott Harding, F. B. Harding, Inc., MD [IM]
    Rep. Independent Electrical Contractors, Inc.

William J. Helfrich, US Department of Labor, PA [E]

Charles F. Mello, Underwriters Laboratories Inc., WA [RT]

Daleep C. Mohla, DCM Electrical Consulting Services, Inc., TX [U]
    Rep. Institute of Electrical & Electronics Engineers, Inc.

Christine T. Porter, Intertek Testing Services, WA [RT]

Gregory J. Steinman, Thomas & Betts Corporation, TN [M]
    Rep. National Electrical Manufacturers Association

Robert G. Stoll, Thomas Associates, Inc., OH [M]
    Rep. Power Tool Institute, Inc

Richard Temblador, Southwire Company, GA [M]
    Rep. The Aluminum Association, Inc.

C. Douglas White, CenterPoint Energy, Inc., TX [UT]
    Rep. Electric Light & Power Group/EEI

David A. Williams, Delta Charter Township, MI [E]
    Rep. International Association of Electrical Inspectors

Alternates

Ron D. Alley, Northern New Mexico IEC, NM [IM]
    (Alt. to G. Scott Harding)
    Rep. Independent Electrical Contractors, Inc.

Joseph P. DeGregoria, Underwriters Laboratories Inc., NY [RT]
    (Alt. to Charles F. Mello)

Ronald Lai, Burndy LLC, NH [M]
    (Alt. to Gregory J. Steinman)
    Rep. National Electrical Manufacturers Association

Paul J. LeVasseur, Bay City JEATC, MI [L]
    (Alt. to Dan Hammel)
    Rep. International Brotherhood of Electrical Workers

Richard E. Loyd, R & N Associates, AZ [M]
    (Alt. to Martin J. Brett, Jr.)
    Rep. American Iron and Steel Institute

Randall R. McCarver, Telcordia Technologies, Inc., NJ [U]
    (Alt. to Trevor N. Bowmer)
    Rep. Alliance for Telecommunications Industry Solutions

Michael E. McNeil, FMC Bio Polymer, ME [U]
    (Alt. to Paul Dobrowsky)
    Rep. American Chemistry Council

Mike O’Meara, Arizona Public Service Company, AZ [UT]
    (Alt. to C. Douglas White)
    Rep. Electric Light & Power Group/EEI

William A. Pancake, III, Universal Engineering Sciences, FL [E]
    (Alt. to David A. Williams)
    Rep. International Association of Electrical Inspectors

Nathan Philips, Integrated Electronic Systems, OR [IM]
    (Alt. to Michael J. Johnston)

Paul R. Picard, Tyco/AFC Cable Systems, Inc., MA [M]
    (Alt. to Richard Temblador)
    Rep. The Aluminum Association, Inc.

Elliot Rappaport, Electro Technology Consultants, Inc., FL [U]
    (Alt. to Daleep C. Mohla)
    Rep. Institute of Electrical & Electronics Engineers, Inc.

Phil Simmons, Simmons Electrical Services, WA [M]
    (Alt. to David Brender)
    Rep. Copper Development Association Inc.

Thomas R. Siwek, Robert Bosch Tool Corporation, IL [M]
    (Alt. to Robert G. Stoll)
    Rep. Power Tool Institute, Inc.

Nonvoting

Robert A. Nelson, Canadian Standards Association, Canada [RT]

CODE-MAKING PANEL NO. 6
Articles 310, 400, 402, Chapter 9 Tables 5 through 9, and Annex B

Scott Cline, Chair
McMurtrey Electric, Inc., CA [IM]
Rep. National Electrical Contractors Association

Samuel B. Friedman, General Cable Corporation, RI [M]
    Rep. National Electrical Manufacturers Association

Robert L. Huddleston, Jr., Eastman Chemical Company, TN [U]
    Rep. American Chemistry Council

Randal Hunter, City of Las Vegas, NV [E]
    Rep. International Association of Electrical Inspectors

G. W. Kent, Kent Electric & Plumbing Systems, TX [IM]
    Rep. Independent Electrical Contractors, Inc.

William F. Laidler, IBEW Local 223 JATC, MA [L]
    Rep. International Brotherhood of Electrical Workers

L. Bruce McClung, Mc Squared Electrical Consulting LLC, WV [U]
    Rep. Institute of Electrical & Electronics Engineers, Inc.

Paul R. Picard, Tyco/AFC Cable Systems, Inc., MA [M]
    Rep. The Aluminum Association, Inc.

John M. Thompson, Underwriters Laboratories Inc., NC [RT]

Carl Timothy Wall, Alabama Power Company, AL [UT]
    Rep. Electric Light & Power Group/EEI

Joseph S. Zimnoch, The Okonite Company, NJ [M]
    Rep. Copper Development Association Inc.

Alternates

Peter E. Bowers, Satellite Electric Company, Inc., MD [IM]
    (Alt. to G. W. Kent)
    Rep. Independent Electrical Contractors, Inc.

John J. Cangemi, Underwriters Laboratories Inc., NY [RT]
    (Alt. to John M. Thompson)

James M. Daly, General Cable, NJ [M]
    (Alt. to Joseph S. Zimnoch)
    Rep. Copper Development Association Inc.

Roland E. Deike, CenterPoint Energy, Inc., TX [UT]
    (Alt. to Carl Timothy Wall)
    Rep. Electric Light & Power Group/EEI

70-13

Richard A. Holub, DuPont Engineering, DE [U]
    (Alt. to Robert L. Huddleston, Jr.)
    Rep. American Chemistry Council

Phillip J. Huff, Inglett & Stubbs LLC, GA [IM]
    (Alt. to Scott Cline)
    Rep. National Electrical Contractors Association

Christel K. Hunter, Alcan Cable, NV [M]
    (Alt. to Paul R. Picard)
    Rep. The Aluminum Association, Inc.

Lowell Lisker, American Insulated Wire Corporation, MA [M]
    (Alt. to Samuel B. Friedman)
    Rep. National Electrical Manufacturers Association

John Stacey, City of St. Louis, MO [E]
    (Alt. to Randal Hunter)
    Rep. International Association of Electrical Inspectors

Donald A. Voltz, BP, TX [U]
    (Alt. to L. Bruce McClung)
    Rep. Institute of Electrical & Electronics Engineers, Inc.

James R. Weimer, Eastern Idaho Electrical JATC, ID [L]
    (Alt. to William F. Laidler)
    Rep. International Brotherhood of Electrical Workers

CODE-MAKING PANEL NO. 7
Articles 320, 322, 324, 326, 328, 330, 332, 334, 336, 338, 340, 382, 394, 396, 398, 399

Michael W. Smith, Chair
Wentzel Electric, MO [IM]
Rep. National Electrical Contractors Association

Thomas H. Cybula, Underwriters Laboratories Inc., NY [RT]

James M. Daly, General Cable, NJ [M]
    Rep. National Electrical Manufacturers Association

Chris J. Fahrenthold, Facilities Solutions Group, TX [IM]
    Rep. Independent Electrical Contractors, Inc.

Herman J. Hall, Austin. TX [M]
    Rep. The Vinyl Institute

James K. Hinrichs, State of Washington, WA [E]
    Rep. International Association of Electrical Inspectors

Christel K. Hunter, Alcan Cable, NV [M]
    Rep. The Aluminum Association, Inc.

Samuel R. La Dart, City of Memphis, TN[L]
    Rep. International Brotherhood of Electrical Workers

Ronald G. Nickson, National Multi Housing Council, DC [U]

Dennis A. Nielsen, Lawrence Berkeley National Laboratory, CA [U]
    Rep. Institute of Electrical & Electronics Engineers, Inc.

John W. Ray, Duke Energy Corporation, NC [UT]
    Rep. Electric Light & Power Group/EEI

Gregory L. Runyon, Eli Lilly and Company, IN [U]
    Rep. American Chemistry Council

David E. Schumacher, Associated Builders and Contractors, IA [IM]
    Rep. Associated Builders & Contractors

George A. Straniero, Tyco/AFC Cable Systems, Inc., NJ [M]
    Rep. Copper Development Association Inc.

Alternates

William B. Crist, Houston Stafford Electric Company, TX [IM]
    (Alt. to Chris J. Fahrenthold)
    Rep. Independent Electrical Contractors, Inc.

Donald G. Dunn, Aramco Services Company, TX [U]
    (Alt. to Dennis A. Nielsen)
    Rep. Institute of Electrical & Electronics Engineers, Inc.

Rachel E. Krepps, Baltimore Gas & Electric Company, MD [UT]
    (Alt. to John W. Ray)
    Rep. Electric Light & Power Group/EEI

Charles David Mercier, Southwire Company, GA [M]
    (Alt. to James M. Daly)
    Rep. National Electrical Manufacturers Association

Keith Owensby, Chattanooga Electrical JATC, TN [L]
    (Alt. to Samuel R. La Dart)
    Rep. International Brotherhood of Electrical Workers

Charles J. Palmieri, Town of Norwell, MA [E]
    (Alt. to James K. Hinrichs)
    Rep. International Association of Electrical Inspectors

Kevin T. Porter, Encore Wire Corporation, TX [M]
    (Alt. to George A. Straniero)
    Rep. Copper Development Association Inc.

Susan L. Stene, Underwriters Laboratories Inc., CA [RT]
    (Alt. to Thomas H. Cybula)

Peter Waldrab, Alcan Cable, PA [M]
    (Alt. to Christel K. Hunter)
    Rep. The Aluminum Association, Inc.

Wesley L. Wheeler, Cogburn Bros., Inc., FL [IM]
    (Alt. to Michael W. Smith)
    Rep. National Electrical Contractors Association

CODE-MAKING PANEL NO. 8
Articles 342, 344, 348, 350, 352, 353, 354, 355, 356, 358, 360, 362, 366, 368, 370, 372, 374, 376, 378, 380,
384, 386, 388, 390, 392, Chapter 9, Tables 1 through 4, and Annex C

Julian R. Burns, Chair
Quality Power Solutions, Inc., NC [IM]
Rep. Independent Electrical Contractors, Inc.

Joyce Evans Blom, The Dow Chemical Company, CA [U]
    Rep. American Chemistry Council

David M. Campbell, Tyco/AFC Cable Systems, Inc., MA [M]
    Rep. The Aluminum Association, Inc.

Joseph Dabe, City of St. Paul, MN [L]
    Rep. International Brotherhood of Electrical Workers

M. Shan Griffith, Elektek, PLLC, TX [U]
    Rep. Institute of Electrical & Electronics Engineers, Inc.

David G. Humphrey, County of Henrico, Virginia, VA [E]
    Rep. International Association of Electrical Inspectors

David H. Kendall, Thomas & Betts Corporation, OH [M]
    Rep. The Vinyl Institute

Richard E. Loyd, R & N Associates, AZ [M]
    Rep. American Iron and Steel Institute

Stephen P. Poholski, Newkirk Electric Associates, Inc., MI [IM]
    Rep. National Electrical Contractors Association

George F. Walbrecht, Underwriters Laboratories Inc., IL [RT]

Rodney J. West, Square D Company/Schneider Electric, OH [M]
    Rep. National Electrical Manufacturers Association

Leslie R. Zielke, South Carolina Electric & Gas Company, SC [UT]
    Rep. Electric Light & Power Group/EEI

70-14

Alternates

Richard J. Berman, Underwriters Laboratories Inc., IL [RT]
    (Alt. to George F. Walbrecht)

Duane A. Carlson, PRS Consulting Engineers, WA [U]
    (Alt. to M. Shan Griffith)
    Rep. Institute of Electrical & Electronics Engineers, Inc.

George R. Dauberger, Thomas & Betts Corporation, TN [M]
    (Alt. to David H. Kendall)
    Rep. The Vinyl Institute

James T. Dwight, Sasol North America, Inc., LA [U]
    (Alt. to Joyce Evans Blom)
    Rep. American Chemistry Council

Kenneth J. Gilbert, Florida Power & Light Company, FL [UT]
    (Alt. to Leslie R. Zielke)
    Rep. Electric Light & Power Group/EEI

Kenneth W. Hengst, EAS Contracting, LP, TX [IM]
    (Alt. to Julian R. Burns)
    Rep. Independent Electrical Contractors, Inc.

James M. Imlah, City of Hillsboro, OR [E]
    (Alt. to David G. Humphrey)
    Rep. International Association of Electrical Inspectors

Gregory L. Maurer, Wheatland Tube Company, PA [M]
    (Alt. to Richard E. Loyd)
    Rep. American Iron and Steel Institute

Gary W. Pemble, Montana Electrical JATC, MT [L]
    (Alt. to Joseph Dabe)
    Rep. International Brotherhood of Electrical Workers

Frederic F. Small, Hubbell Incorporated, CT [M]
    (Alt. to Rodney J. West)
    Rep. National Electrical Manufacturers Association

Richard Temblador, Southwire Company, GA [M]
    (Alt. to David M. Campbell)
    Rep. The Aluminum Association, Inc.

CODE-MAKING PANEL NO. 9
Articles 312, 314, 404, 408, 450, 490

Robert A. McCullough, Chair
Tuckerton, NJ [E]
Rep. International Association of Electrical Inspectors

Rodney D. Belisle, NECA-IBEW Electrical Training Trust, OR [L]
    Rep. International Brotherhood of Electrical Workers

Billy Breitkreutz, Fluor Corporation, TX [U]
    Rep. Associated Builders & Contractors

Paul D. Coghill, Intertek Testing Services, OH [RT]

Richard P. Fogarty, Consolidated Edison Company of New York, Inc., NY [UT]
    Rep. Electric Light & Power Group/EEI

Frederic P. Hartwell, Hartwell Electrical Services, Inc., MA [SE]

Thomas J. LeMay, LeMay Electric, Inc., GA [IM]
    Rep. Independent Electrical Contractors, Inc.

Robert D. Osborne, Underwriters Laboratories Inc., NC [RT]

Bradford D. Rupp, Allied Moulded Products, Inc., OH [M]
    Rep. National Electrical Manufacturers Association

Sukanta Sengupta, FMC Corporation, NJ [U]
    Rep. Institute of Electrical & Electronics Engineers, Inc.

Monte Szendre, Wilson Construction Company, OR [IM]
Rep. National Electrical Contractors Association

Ralph H. Young, Eastman Chemical Company, TN [U]
    Rep. American Chemistry Council

Alternates

Kevin J. Breen, Breen Electrical Contractors Inc., NY [IM]
    (Alt. to Thomas J. LeMay)
    Rep. Independent Electrical Contractors, Inc.

Robert R. Gage, National Grid, NY [UT]
    (Alt. to Richard P. Fogarty)
    Rep. Electric Light & Power Group/EEI

L. Keith Lofland, International Association of Electrical
    Inspectors (IAEI), TX [E]
    (Alt. to Robert A. McCullough)

Kenneth L. McKinney, Jr., Underwriters Laboratories Inc.,
    NC [RT]
    (Alt. to Robert D. Osborne)

Paul W. Myers, Potash Corporation, OH [U]
    (Alt. to Sukanta Sengupta)
    Rep. Institute of Electrical & Electronics Engineers, Inc.

Ronnie H. Ridgeway, Siemens Industry, Inc., TX [M]
    (Alt. to Bradford D. Rupp)
    Rep. National Electrical Manufacturers Association

Rhett A. Roe, IBEW Local Union 26 JATC, MD [L]
    (Alt. to Rodney D. Belisle)
    Rep. International Brotherhood of Electrical Workers

CODE-MAKING PANEL NO. 10
Article 240

Donald R. Cook, Chair
Shelby County Development Services, AL [E]
Rep. International Association of Electrical Inspectors

Madeline Borthick, IEC of Houston, Inc., TX [IM]
    Rep. Independent Electrical Contractors, Inc.

Dennis M. Darling, Stantec, Canada [U]
    Rep. Institute of Electrical & Electronics Engineers, Inc.

James T. Dollard, Jr., IBEW Local Union 98, PA [L]
    Rep. International Brotherhood of Electrical Workers

Charles Eldridge, Indianapolis Power & Light Company, IN [UT]
    Rep. Electric Light & Power Group/EEI

Carl Fredericks, The Dow Chemical Company, TX [U]
    Rep. American Chemistry Council

Roderic Hageman, PRIT Service, Inc., IL [IM]
    Rep. InterNational Electrical Testing Association

Jeffrey H. Hidaka, Underwriters Laboratories Inc., IL [RT]

Alan Manche, Square D Company/Schneider Electric, KY [M]
    Rep. National Electrical Manufacturers Association

Robert W. Mount, Jr., Hussmann Corporation, MO [M]
    Rep. Air-Conditioning, Heating, & Refrigeration Institute

George J. Ockuly, Technical Marketing Consultants, MO [M]

Richard Sobel, Quantum Electric Corporation, NY [IM]
    Rep. National Electrical Contractors Association

Alternates

Scott A. Blizard, American Electrical Testing Company, Inc., MA [IM]
    (Alt. to Roderic Hageman)
    Rep. International Electrical Testing Association

70-15

Robert J. Kauer, Building Inspection Underwriters, Inc., PA [E]
    (Alt. to Donald R. Cook)
    Rep. International Association of Electrical Inspectors

Frank G. Ladonne, Underwriters Laboratories Inc., IL [RT]
    (Alt. to Jeffrey H. Hidaka)

Kevin J. Lippert, Eaton Corporation, PA [M]
    (Alt. to Alan Manche)
    Rep. National Electrical Manufacturers Association

Richard E. Lofton, II, IBEW Local Union 280, OR [L]
    (Alt. to James T. Dollard, Jr.)
    Rep. International Brotherhood of Electrical Workers

Vincent J. Saporita, Cooper Bussmann, MO [M]
    (Alt. to George J. Ockuly)

Roy K. Sparks, III, Eli Lilly and Company, IN [U]
    (Alt. to Carl Fredericks)
    Rep. American Chemistry Council

Steve A. Struble, Freeman’s Electric Service, Inc., SD [IM]
    (Alt. to Madeline Borthick)
    Rep. Independent Electrical Contractors, Inc.

Steven E. Townsend, General Motors Corporation, MI [U]
    (Alt. to Dennis M. Darling)
    Rep. Institute of Electrical & Electronics Engineers, Inc.

John F. Vartanian, National Grid, MA [UT]
    (Alt. to Charles Eldridge)
    Rep. Electric Light & Power Group/EEI

CODE-MAKING PANEL NO. 11
Articles 409, 430, 440, 460, 470, Annex D, Example D8

Wayne Brinkmeyer, Chair
Britain Electric Company, TX [IM]
Rep. National Electrical Contractors Association

Terry D. Cole, Hamer Electric, Inc., WA [IM]
    Rep. Independent Electrical Contractors, Inc.

Jeffrey A. DesJarlais, Underwriters Laboratories Inc., IL [RT]

James M. Fahey, IBEW Local Union 103/MBTA, MA [L]
    Rep. International Brotherhood of Electrical Workers

Robert G. Fahey, City of Janesville, WI [E]
    Rep. International Association of Electrical Inspectors

William D. Glover, PPG Industries, Inc., WV [U]
    Rep. American Chemistry Council

Paul E. Guidry, Fluor Enterprises, Inc., TX [U]
    Rep. Associated Builders & Contractors

Paul S. Hamer, Chevron Energy Technology Company, CA [U]
    Rep. American Petroleum Institute

James C. Missildine, Jr., Southern Company Services, Inc., AL [UT]
    Rep. Electric Light & Power Group/EEI

Vincent J. Saporita, Cooper Bussmann, MO [M]

Lynn F. Saunders, Brighton, MI [U]
    Rep. Institute of Electrical & Electronics Engineers, Inc.

Lawrence E. Todd, Intertek Testing Services, OR [RT]

Ron Widup, Shermco Industries, Inc., TX [IM]
    Rep. InterNational Electrical Testing Association

James R. Wright, Siemens Industry, Inc., IL [M]
    Rep. National Electrical Manufacturers Association

Alternates

Stanley J. Folz, Morse Electric Company, NV [IM]
    (Alt. to Wayne Brinkmeyer)
    Rep. National Electrical Contractors Association

Philip C. Hack, Constellation Energy Power Generation, MD [UT]
    (Alt. to James C. Missildine, Jr.)
    Rep. Electric Light & Power Group/EEI

Barry G. Karnes, Underwriters Laboratories Inc., CA [RT]
    (Alt. to Jeffrey A. DesJarlais)

Ed Larsen, Square D Company/Schneider Electric, IA [M]
    (Alt. to James R. Wright)
    Rep. National Electrical Manufacturers Association

Thomas E. Moore, City of Beachwood, OH [E]
    (Alt. to Robert G. Fahey)
    Rep. International Association of Electrical Inspectors

Arthur S. Neubauer, Arseal Technologies, GA [U]
    (Alt. to Paul S. Hamer)
    Rep. American Petroleum Institute

Jebediah J. Novak, Cedar Rapids Electrical JATC, IA [L]
    (Alt. to James M. Fahey)
    Rep. International Brotherhood of Electrical Workers

George J. Ockuly, Technical Marketing Consultants, MO [M]
    (Alt. to Vincent J. Saporita)

Charles L. Powell, Eastman Chemical Company, TN [U]
    (Alt. to William D. Glover)
    Rep. American Chemistry Council

Arthur J. Smith, III, Waldemar S. Nelson & Company, Inc., LA [U]
    (Alt. to Lynn F. Saunders)
    Rep. Institute of Electrical & Electronics Engineers, Inc.

L. Matthew Snyder, Intertek Testing Services, NY [RT]
    (Alt. to Lawrence E. Todd)

Russell A. Tiffany, R. A. Tiffany & Associates, PA [M]
    (Voting Alt. to AHRI Rep.)
    Rep. Air-Conditioning, Heating, & Refrigeration Institute

Michael K. Weitzel, Central Washington Electrical Education, WA [IM]
    (Alt. to Terry D. Cole)
    Rep. Independent Electrical Contractors, Inc.

CODE-MAKING PANEL NO. 12
Articles 610, 620, 625, 626, 630, 640, 645, 647, 650, 660, 665, 668, 669, 670, 685,
Annex D, Examples D9 and D10

Timothy M. Croushore, Chair
Allegheny Power, PA [UT]
Rep. Electric Light & Power Group/EEI

William E. Anderson, The Procter & Gamble Company, OH [U]
    Rep. Institute of Electrical & Electronics Engineers, Inc.

Thomas R. Brown, Intertek Testing Services, NY [RT]

Karl M. Cunningham, Alcoa, Inc., PA [M]
    Rep. The Aluminum Association, Inc.
    (VL to 610, 625, 630, 645, 660, 665, 668, 669, 685)

Thomas L. Hedges, Hedges Electric & Construction Inc., CA [IM]
    Rep. National Electrical Contractors Association

Michael J. Hittel, GM Worldwide Facilities Group, MI [U]
    Rep. Society of Automotive Engineers-Hybrid Committee

70-16

Robert E. Johnson, ITE Safety, MA [U]
    Rep. Information Technology Industry Council
    (VL to 640, 645, 647, 685)

Andy Juhasz, Kone, Inc., IL [M]
    Rep. National Elevator Industry Inc.
    (VL to 610, 620, 630)

Stanley Kaufman, CableSafe, Inc./OFS, GA [M]
    Rep. Society of the Plastics Industry, Inc.
    (VL to 640, 645)

John R. Kovacik, Underwriters Laboratories Inc., IL [RT]

Todd Lottmann, Cooper Bussmann, MO [M]
    Rep. National Electrical Manufacturers Association

Sam Marcovici, New York City Department of Buildings, NY [E]

Tim McClintock, Wayne County, Ohio, OH [E]
    Rep. International Association of Electrical Inspectors

David R. Quave, IBEW Local Union 903, MS [L]
    Rep. International Brotherhood of Electrical Workers

Duke W. Schamel, Electrical Service Solutions, Inc., CO [IM]
    Rep. Independent Electrical Contractors, Inc.

Arthur E. Schlueter, Jr., A. E. Schlueter Pipe Organ Company, GA [M]
    Rep. American Institute of Organ Builders
    (VL to 640, 650)

Robert C. Turner, Inductotherm Corporation, MD [M]
    (VL to 610, 630, 665, 668, 669)

Ryan Gregory Ward, ldleAire, Inc., TN [U]
    Rep. Transportation Electrification Committee
    (VL to 625, 626)

Kenneth White, Olin Corporation, NY [U]
    Rep. American Chemistry Council

Alternates

Timothy M. Andrea, Southwire Company, GA [M]
    (Alt. to Karl M. Cunningham)
    Rep. The Aluminum Association, Inc.
    (VL to 610, 625, 630, 645, 660, 665, 668, 669, 685)

Jeffrey W. Blain, Schindler Elevator Corporation, NY [M]
    (Alt. to Andy Juhasz)
    Rep. National Elevator Industry Inc.
    (VL to 610, 620, 630)

Thomas M. Burke, Underwriters Laboratories Inc., CA [RT]
    (Alt. to John R. Kovacik)

Jeffrey L. Holmes, IBEW Local Union 1 JATC, MO [L]
    (Alt. to David R. Quave)
    Rep. International Brotherhood of Electrical Workers

Gery J. Kissel, General Motors Corporation, MI [U]
    (Alt. to Michael J. Hittel)
    Rep. Society of Automotive Engineers-Hybrid Committee

Todd R. Konieczny, Intertek Testing Services, MA [RT]
    (Alt. to Thomas R. Brown)

Christopher P. O’Neil, NSTAR Electric & Gas Corporation, MA [UT]
    (Alt. to Timothy M. Croushore)
    Rep. Electric Light & Power Group/EEI

David L. Sher, City of Bellevue, WA [E]
    (Alt. to Tim McClintock)
    Rep. International Association of Electrical Inspectors

Emad Tabatabaei, Inductotherm Corporation, NJ [M]
    (Alt. to Robert C. Turner)
    (VL to 610, 630, 665, 668, 669)

Lori L. Tennant, Square D Company/Schneider Electric, NC [M]
    (Alt. to Todd Lottmann)
    Rep. National Electrical Manufacturers Association

Stephen J. Thorwegen, Jr., FSG Electric, TX [IM]
    (Alt. to Duke W. Schamel)
    Rep. Independent Electrical Contractors, Inc.

Charles M. Trout, Maron Electric Company, FL [IM]
    (Alt. to Thomas L. Hedges)
    Rep. National Electrical Contractors Association

Nonvoting

Andre R. Cartal, Yardley, PA [E] (Member Emeritus)

CODE-MAKING PANEL NO. 13
    Articles 445, 455, 480, 695, 700, 701, 702, 708, Annex F, and Annex G

Donald P. Bliss, Chair
NI2 Center for Infrastructure Expertise, NH [U]

Martin D. Adams, Adams Electric, Inc., CO [IM]
    Rep. National Electrical Contractors Association

Suzanne M. Borek, New Jersey Department of Community Affairs, NJ [E]
    Rep. International Association of Electrical Inspectors

James L. Brown, Detroit Edison, DTE Energy, MI [UT]
    Rep. Electric Light & Power Group/EEI

Daniel J. Caron, Bard, Rao + Athanas Consulting Engineers, LLC, MA [SE]

James S. Conrad, Tyco Thermal Controls, CT [M]
    Rep. Copper Development Association Inc.

Richard D. Currin, Jr., North Carolina State University, NC [U]
    Rep. American Society of Agricultural & Biological Engineers

Neil A. Czarnecki, Reliance Controls Corporation, WI [M]
    Rep. National Electrical Manufacturers Association

Herbert H. Daugherty, Electric Generating Systems Association, NJ [M]

James E. Degnan, Sparling, WA [U]
    Rep. American Society for Healthcare Engineering

Ronald A. Keenan, M. C. Dean, Inc., VA [IM]
    Rep. Independent Electrical Contractors, Inc.

Linda J. Little, IBEW Local 1 Electricians JATC, MO [L]
    Rep. International Brotherhood of Electrical Workers

Craig A. Mouton, ExxonMobil Chemical Corporation, TX [U]
    Rep. American Chemistry Council

Mark C. Ode, Underwriters Laboratories Inc., AZ [RT]

Gary L. Olson, Cummins Power Generation, MN [M]

Michael L. Savage, Sr., Middle Department Inspection Agency, Inc., MD [E]

Mario C. Spina, Verizon Wireless, OH [U]
    Rep. Institute of Electrical & Electronics Engineers, Inc.

David Tobias, Jr., Intertek Testing Services, OH [RT]

Alternates

Barry S. Bauman, Alliant Energy, WI [U]
    (Alt. to Richard D. Currin, Jr.)
    Rep. American Society of Agricultural & Biological Engineers

Steven A. Corbin, Corbin Solar Solutions LLC, NJ [IM]
    (Alt. to Ronald A. Keenan)
    Rep. Independent Electrical Contractors, Inc.

James T. Dollard, Jr., IBEW Local Union 98, PA [L]
    (Alt. to Linda J. Little)
    Rep. International Brotherhood of Electrical Workers

Lawrence W. Forshner, Cummins Northeast, Inc., MA [M]
    (Alt. to Gary L. Olson)

Chad Kennedy, Square D Company/Schneider Electric, SC [M]
    (Alt. to Neil A. Czarnecki)
    Rep. National Electrical Manufacturers Association

John R. Kovacik, Underwriters Laboratories Inc., IL [RT]
    (Alt. to Mark C. Ode)

70-17

Peter M. Olney, Vermont Department of Public Safety, VT [E]
    (Alt. to Suzanne M. Borek)
    Rep. International Association of Electrical Inspectors

Bayly Morgan Tyler, Consolidated Edison Company of New York Inc., NY [UT]
    (Alt. to James L. Brown)
    Rep. Electric Light & Power Group/EEI

Herbert V. Whittall, Electrical Generating Systems Association, FL [M]
    (Alt. to Herbert H. Daugherty)

CODE-MAKING PANEL NO. 14
Articles 500, 501, 502, 503, 504, 505, 506, 510, 511, 513, 514, 515, and 516

Robert A. Jones, Chair
Independent Electrical Contractors, Inc., TX [IM]
Rep. Independent Electrical Contractors, Inc.

Daniel Batta, Jr., Constellation Power Source Generation, Inc., MD [UT]
    Rep. Electric Light & Power Group/EEI

Marc J. Bernsen, National Electrical Contractors Association, ID [IM]
    Rep. National Electrical Contractors Association

Edward M. Briesch, Underwriters Laboratories Inc., IL [RT]

James D. Cospolich, Waldemar S. Nelson & Company Inc., LA [U]
    Rep. Institute of Electrical & Electronics Engineers, Inc.

Mark Goodman, Jacobs Engineering Group, CA [U]
    Rep. American Petroleum Institute

Joseph H. Kuczka, Killark Electric Manufacturing Company, MO [M]
    Rep. National Electrical Manufacturers Association

William G. Lawrence, Jr., FM Global, MA [I]

L. Evans Massey, Baldor Electric Company, SC [M]
    Rep. Instrumentation, Systems, & Automation Society

Jeremy Neagle, Intertek Testing Services, NY [RT]

Donald R. Offerdahl, North Dakota State Electrical Board, ND [E]
    Rep. International Association of Electrical Inspectors

John L. Simmons, Florida East Coast JATC, FL [L]
    Rep. International Brotherhood of Electrical Workers

David B. Wechsler, The Dow Chemical Company, TX [U]
    Rep. American Chemistry Council

Mark C. Wirfs, R & W Engineering, Inc., OR [U]
    Rep. Grain Elevator and Processing Society

Alternates

Harold G. Alexander, American Electric Power Company, OH [UT]
    (Alt. to Daniel Batta, Jr.)
    Rep. Electric Light & Power Group/EEI

Donald W. Ankele, Underwriters Laboratories Inc., IL [RT]
    (Alt. to Edward M. Briesch)

Steven J. Blais, EGS Electrical Group, IL [M]
    (Alt. to Joseph H. Kuczka)
    Rep. National Electrical Manufacturers Association

Mark W. Bonk, Cargill Incorporated, MN [U]
    (Alt. to Mark C. Wirfs)
    Rep. Grain Elevator and Processing Society

Dave Burns, Shell Exploration & Production Company, TX [U]
    (Alt. to Mark Goodman)
    Rep. American Petroleum Institute

Larry W. Burns, Burns Electric, Inc., TX [IM]
    (Alt. to Robert A. Jones)
    Rep. Independent Electrical Contractors, Inc.

Jonathan L. Cadd, International Association of Electrical Inspectors, TX [E]
    (Alt. to Donald R. Offerdahl)

Thomas E. Dunne, Long Island Joint Apprenticeship & Training Committee, NY [L]
    (Alt. to John L. Simmons)
    Rep. International Brotherhood of Electrical Workers

Richard A. Holub, DuPont Engineering, DE [U]
    (Alt. to David B. Wechsler)
    Rep. American Chemistry Council

Ted H. Schnaare, Rosemount Incorporated, MN [M]
    (Alt. to L. Evans Massey)
    Rep. Instrumentation, Systems, & Automation Society

Donald W. Zipse, Zipse Electrical Forensics, LLC, PA [U]
    (Alt. to James D. Cospolich)
    Rep. Institute of Electrical & Electronics Engineers, Inc.

Nonvoting

Timothy J. Pope, Canadian Standards Association, Canada [RT]

Eduardo N. Solano, Estudio Ingeniero Solano S.A., Argentina [SE]

Fred K. Walker, US Department of the Air Force, FL [U]
    Rep. TC on Airport Facilities

CODE-MAKING PANEL NO. 15
Articles 517, 518, 520, 522, 525, 530, 540

Donald J. Talka, Chair
Underwriters Laboratories Inc., NY [RT]

James R. Duncan, Sparling Electrical Engineering & Technology Consulting, WA [U]
    Rep. Institute of Electrical & Electronics Engineers, Inc.

Ronald E. Duren, PacifiCorp, WA [UT]
    Rep. Electric Light & Power Group/EEI

Douglas S. Erickson, American Society for Healthcare Engineering, VI [U]
    Rep. American Society for Healthcare Engineering

Mitchell K. Hefter, Entertainment Technology/Philips, TX [IM]
    Rep. Illuminating Engineering Society of North America
    (VL to 518, 520, 525, 530, 540)

Kim Jones, Funtastic Shows, OR [U]
    Rep. Outdoor Amusement Business Association. Inc.
    (VL to 525)

Edwin S. Kramer, Radio City Music Hall, NY [L]
    Rep. International Alliance of Theatrical Stage Employees
    (VL to 518, 520, 525, 530, 540)

Larry Lau, US Department of Veterans Affairs, DC [U]
    (VL to 517, 518)

Stephen M. Lipster, The Electrical Trades Center, OH [L]
    Rep. International Brotherhood of Electrical Workers

Hugh O. Nash, Jr., Nash Lipsey Burch, LLC, TN [SE]
    Rep. TC on Electrical Systems

70-18

Kevin T. Porter, Encore Wire Corporation, TX [M]
    Rep. The Aluminum Association, Inc.

Marcus R. Sampson, Minnesota Department of Labor & Industry, MN [E]
    Rep. International Association of Electrical Inspectors

James C. Seabury III, Enterprise Electric, LLC, TN [IM]
    Rep. Independent Electrical Contractors, Inc.

Bruce D. Shelly, Shelly Electric Company, Inc., PA [IM]
    Rep. National Electrical Contractors Association

Michael D. Skinner, CBS Studio Center, CA [U]
    Rep. Alliance of Motion Picture and Television Producers
    (VL to 518, 520, 525, 530, 540)

Kenneth E. Vannice, Leviton Manufacturing Company Inc., OR [M]
    Rep. US Institute for Theatre Technology
    (VL to 518, 520, 525, 530, 540)

Michael Velvikis, High Voltage Maintenance Corporation, WI [IM]
    Rep. InterNational Electrical Testing Association

James L. Wiseman, Square D Company/Schneider Electric, TN [M]
    Rep. National Electrical Manufacturers Association

Alternates

Gary A. Beckstrand, Utah Electrical JATC, UT [L]
    (Alt. to Stephen M. Lipster)
    Rep. International Brotherhood of Electrical Workers

James L. Brown, Detroit Edison, DTE Energy, MI [UT]
    (Alt. to Ronald E. Duren)
    Rep. Electric Light & Power Group/EEI

Matthew B. Dozier, IDesign Services, TN [U]
    (Alt. to James R. Duncan)
    Rep. Institute of Electrical & Electronics Engineers, Inc.

Samuel B. Friedman, General Cable Corporation, RI [M]
    (Alt. to James L. Wiseman)
    Rep. National Electrical Manufacturers Association

Steven R. Goodman, Alcan Cable, PA [M]
    (Alt. to Kevin T. Porter)
    Rep. The Aluminum Association, Inc.

Dennis W. Marshall, D & L Electric Company, TX [IM]
    (Alt. to James C. Seabury III)
    Rep. Independent Electrical Contractors, Inc.

Joseph P. Murnane, Jr., Underwriters Laboratories Inc., NY [RT]
    (Alt. to Donald J. Talka)

Richard E. Pokorny, City of Marshfield, Wisconsin, WI [E]
    (Alt. to Marcus R. Sampson)
    Rep. International Association of Electrical Inspectors

Steven R. Terry, Electronic Theatre Controls Inc., NY [M]
    (Alt. to Kenneth E. Vannice)
    Rep. US Institute for Theatre Technology
    (VL to 518, 520, 525, 530, 540)

CODE-MAKING PANEL NO. 16
Articles 770, 800, 810, 820, 830, 840

Ron L. Janikowski, Chair
City of Wausau, Wisconsin, WI [E]
Rep. International Association of Electrical Inspectors

Donna Ballast, dbi, TX [M]
    Rep. Telecommunications Industry Association

George Bish, MasTec, Inc., dba Advanced Technologies, NC [IM]
    Rep. Satellite Broadcasting & Communications Association

J. Robert Boyer, GE Security, NJ [M]
    Rep. National Electrical Manufacturers Association

James E. Brunssen, Telcordia, NJ [U]
    Rep. Alliance for Telecommunications Industry Solutions

Gerald Lee Dorna, Belden Wire & Cable Co., IN [M]
    Rep. Insulated Cable Engineers Association Inc.

Ralph M. Esemplare, Consolidated Edison Company of New York, NY [UT]
    Rep. Electric Light & Power Group/EEI

Dale R. Funke, Shell Oil Company, TX [U]
    Rep. American Chemistry Council

Roland W. Gubisch, Intertek Testing Services, MA [RT]

Randolph J. Ivans, Underwriters Laboratories Inc., NY [RT]

Robert W. Jensen, dbi-Telecommunication Infrastructure Design, TX [M]
    Rep. Building Industry Consulting Services International

Steven C. Johnson, Johnson Telecom, LLC, NC [UT]
    Rep. National Cable & Telecommunications Association

William J. McCoy, Telco Sales, Inc., TX [U]
    Rep. Institute of Electrical & Electronics Engineers, Inc.

Harold C. Ohde, IBEW-NECA Technical Institute, IL [L]
    Rep. International Brotherhood of Electrical Workers

W. Douglas Pirkle, Pirkle Electric Company, Inc., GA [IM]
    Rep. National Electrical Contractors Association

Luigi G. Prezioso, M. C. Dean, Inc., VA [IM]
    Rep. Independent Electrical Contractors, Inc.

Alternates

Trevor N. Bowmer, Telcordia Technologies, NJ [U]
    (Alt. to James E. Brunssen)
    Rep. Alliance for Telecommunications Industry Solutions

Terry C. Coleman, National Joint Apprentice & Training Committee, TN [L]
    (Alt. to Harold C. Ohde)
    Rep. International Brotherhood of Electrical Workers

Timothy D. Cooke, Times Fiber Communications, Inc., VA [UT]
    (Alt. to Steven C. Johnson)
    Rep. National Cable & Telecommunications Association

Jeff Fitzloff, State of Idaho Division of Building Safety, ID [E]
    (Alt. to Ron L. Janikowski)
    Rep. International Association of Electrical Inspectors

John A. Kacperski, Tele Design Services, CA [M]
    (Alt. to Robert W. Jensen)
    Rep. Building Industry Consulting Services International

Roderick S. Kalbfleisch, Northeast Utilities, CT [UT]
    (Alt. to Ralph M. Esemplare)
    Rep. Electric Light & Power Group/EEI

Stanley Kaufman, CableSafe, Inc./OFS, GA [M]
    (Alt. to Gerald Lee Dorna)
    Rep. Insulated Cable Engineers Association Inc.

David M. Lettkeman, Dish Network Service, LLC, CO [IM]
    (Alt. to George Bish)
    Rep. Satellite Broadcasting & Communications Association

Jack McNamara, Bosch Security Systems, NY [M]
    (Alt. to J. Robert Boyer)
    Rep. National Electrical Manufacturers Association

Craig Sato, Underwriters Laboratories Inc., CA [RT]
    (Alt. to Randolph J. Ivans)

David B. Schrembeck, DBS Communications, Inc., OH [IM]
    (Alt. to Luigi G. Prezioso)
    Rep. Independent Electrical Contractors, Inc.

Mario C. Spina, Verizon Wireless, OH |U]
    (Alt. to William J. McCoy)
    Rep. Institute of Electrical & Electronics Engineers, Inc.

James T. Sudduth, Intertek Testing Services, KY [RT]
    (Alt. to Roland W. Gubisch)

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CODE-MAKING PANEL NO. 17
Articles 422, 424, 426, 427, 680, 682

Don W. Jhonson, Chair
Interior Electric, Inc., FL [IM]
Rep. National Electrical Contractors Association

Thomas V. Blewitt, Underwriters Laboratories Inc., NY [RT]

Paul Crivell, Camp, Dresser, & McKee Inc., WA [U]
    Rep. Institute of Electrical & Electronics Engineers, Inc.

Christopher S. Gill, New York Board of Fire Underwriters, NY [E]

Bruce R. Hirsch, Baltimore Gas & Electric Company, MD [UT]
    Rep. Electric Light & Power Group/EEI

James E. Maldonado, City of Tempe, AZ [E]
    Rep. International Association of Electrical Inspectors

Wayne E. Morris, Association of Home Appliance Manufacturers, DC [M]
    (VL to 422, 424)

Jurgen Pannock, Whirlpool Corporation, TN [M]
    Rep. Air-Conditioning, Heating, & Refrigeration Institute
    (VL to 422, 424)

Marcos Ramirez, Hatfield-Reynolds Electric company, AZ [IM]
    Rep. Independent Electrical Contractors, Inc.

Brian E. Rock, Hubbell Incorporated, CT [M]
    Rep. National Electrical Manufacturers Association

Ronald F. Schapp, Intertek Testing Services, OH [RT]

Kenneth M. Shell, Tyco Thermal Controls, CA [M]
    Rep. Copper Development Association Inc.
    (VL to 426, 427)

Ronald Sweigart, E.I. duPont de Nemours & Company, Inc., DE [U]
    (VL to 422, 424, 426, 427, 682)

Lee L. West, Newport Controls, LLC, CA [M]
    Rep. Association of Pool & Spa Professionals
    (VL to 680)

Randy J. Yasenchak, IBEW Local Union 607, PA [L]
    Rep. International Brotherhood of Electrical Workers

Alternates

Dennis L. Baker, Springs & Sons Electrical Contractors Inc., AZ [IM]
    (Alt. to Marcos Ramirez)
    Rep. Independent Electrical Contractors, Inc.

Bobby J. Gray, Hoydar/Buck, Inc., WA [IM]
    (Alt. to Don W. Jhonson)
    Rep. National Electrical Contractors Association

E. P. Hamilton, III, E. P. Hamilton & Associates, Inc., TX [M]
    (Alt. to Lee L. West)
    Rep. Association of Pool & Spa Professionals
    (VL to 680)

Robert M. Milatovich, Clark County Building Department, NV [E]
    (Alt. to James E. Maldonado)
    Rep. International Association of Electrical Inspectors

Brian Myers, IBEW Local Union 98, PA [L]
    (Alt. to Randy J. Yasenchak)
    Rep. International Brotherhood of Electrical Workers

Stephen C. Richbourg, Gulf Power Company, FL [UT]
    (Alt. to Bruce R. Hirsch)
    Rep. Electric Light & Power Group/EEI

Patrick G. Salas, GE Consumer and Industrial, CT [M]
    (Alt. to Brian E. Rock)
    Rep. National Electrical Manufacturers Association

Chester L. Sandberg, Shell Exploration & Production Inc., CA [U]
    (Alt. to Paul Crivell)
    Rep. Institute of Electrical & Electronics Engineers, Inc.

Gary L. Siggins, Underwriters Laboratories Inc., CA [RT]
    (Alt. to Thomas V. Blewitt)

Kam Fai Siu, Intertek, China [RT]
    (Alt. to Ronald F. Schapp)

Nonvoting

Douglas A. Lee, US Consumer Product Safety Commission, MD [C]
    (Alt. to Andrew M. Trotta)

Andrew M. Trotta, US Consumer Product Safety Commission, MD [C]
    (Alt. to Douglas A. Lee)

CODE-MAKING PANEL NO. 18
Articles 406, 410, 411, 600, 605

Michael N. Ber, Chair
IEC, Houston, TX [IM]
    Rep. Independent Electrical Contractors, Inc.

Frederick L. Carpenter, Lithonia Lighting, GA [M]
    Rep. National Electrical Manufacturers Association

Paul Costello, NECA and IBEW Local 90 JATC, CT [L]
    Rep. International Brotherhood of Electrical Workers

Lee C. Hewitt, Underwriters Laboratories Inc., IL [RT]

Melvyn J. Kochan, Young Electric Sign Company, NV [M]
    Rep. International Sign Association
    (VL to 600)

Steven A. Larson, MS Technology, Inc., TN [U]
    Rep. Institute of Electrical & Electronics Engineers, Inc.

Amos D. Lowrance, Jr., City of Chattanooga, Tennessee, TN [E]
    Rep. International Association of Electrical Inspectors

Michael S. O’Boyle, Philips-Lightolier, MA [M]
    Rep. American Lighting Association
    (VL to 410, 411)

James F. Pierce, Intertek Testing Services, OR [RT]

Sondra K. Todd, Westar Energy, Inc., KS [UT]
    Rep. Electric Light & Power Group/EEI

Charles M. Trout, Maron Electric Company, FL [IM]
    Rep. National Electrical Contractors Association

Jack Wells, Pass & Seymour/Legrand, NC [M]

Randall K. Wright, RKW Consulting, PA [SE]

Alternates

Steve Campolo, Leviton Manufacturing Company, Inc., NY [M]
    (Alt. to Frederick L. Carpenter)
    Rep. National Electrical Manufacturers Association

Robert T. Carlock, R. T. Carlock Company, TN [IM]
    (Alt. to Michael N. Ber)
    Rep. Independent Electrical Contractors, Inc.

Larry Chan, City of New Orleans, LA [E]
    (Alt. to Amos D. Lowrance, Jr.)
    Rep. International Association of Electrical Inspectors

70-20

David D’Hooge, ComEd, IL [UT]
    (Alt. to Sondra K. Todd)
    Rep. Electric Light & Power Group/EEI

Richard D. Gottwald, International Sign Association, VA [M]
    (Alt. to Melvyn J. Kochan)
    Rep. International Sign Association
    (VL to 600)

Charles S. Kurten, Underwriters Laboratories Inc., NY [RT]
    (Alt. to Lee C. Hewitt)

Terry K. McGowan, Lighting Ideas, Inc., OH [M]
    (Alt. to Michael S. O’Boyle)
    Rep. American Lighting Association
    (VL to 410, 411)

Jesse Sprinkle, IBEW Local 461, IL [L]
    (Alt. to Paul Costello)
    Rep. International Brotherhood of Electrical Workers

Chandresh Thakur, Intertek Testing Services, CA [RT]
    (Alt. to James F. Pierce)

CODE-MAKING PANEL NO. 19
Articles 545, 547, 550, 551, 552, 553, 555, 604, 675, and Annex D, Examples D11 and D12

Leslie Sabin-Mercado, Chair
San Diego Gas & Electric Company, CA [UT]
Rep. Electric Light & Power Group/EEI

Barry S. Bauman, Alliant Energy, WI [U]
    Rep. American Society of Agricultural & Biological Engineers

Ron B. Chilton, North Carolina Department of Insurance, NC [E]
    Rep. International Association of Electrical Inspectors

Garry D. Cole, Shelby/Mansfield KOA, OH [U]
    Rep. National Association of RV Parks & Campgrounds
    (VL to 550, 551, 552)

Steven R. Goodman, Alcan Cable, PA [M]
    Rep. The Aluminum Association. Inc.

Bruce A. Hopkins, Recreation Vehicle Industry Association, VA [M]
    (VL to 550, 551, 552)

Howard D. Hughes, Hughes Electric Company Inc., AR [IM]
    Rep. National Electrical Contractors Association

David W. Johnson, CenTex IEC, TX [IM]
    Rep. Independent Electrical Contractors, Inc.

Thomas R. Lichtenstein, Underwriters Laboratories Inc., IL [RT]

Timothy P. McNeive, Thomas & Betts Corporation, TN [M]
    Rep. National Electrical Manufacturers Association

Ronald Michaelis, South Bend & Vicinity Electrical JATC, IN [L]
    Rep. International Brotherhood of Electrical Workers

Doug Mulvaney, Kampgrounds of America, Inc., MT [U]
    (VL to 550, 551, 552, 555)

Michael L. Zieman, RADCO, CA [RT]
    (VL to 545, 550, 551, 552)

Alternates

Glenn H. Ankenbrand, Delmarva Power, MD [UT]
    (Alt. to Leslie Sabin-Mercado)
    Rep. Electric Light & Power Group/EEI

Michael B. F. Atkinson, Kampgrounds of America. Inc., MT [U]
    (Alt. to Doug Mulvaney)
    (VL to 550, 551, 552, 555)

William Bruce Bowman, Fox Systems, Inc., GA [IM]
    (Alt. to David W. Johnson)
    Rep. Independent Electrical Contractors, Inc.

Robert J. Fick, Alliant Energy, WI [U]
    (Alt. to Barry S. Bauman)
    Rep. American Society of Agricultural & Biological Engineers

John P. Goodsell, Hubbell Incorporated, CT [M]
    (Alt. to Timothy P. McNeive)
    Rep. National Electrical Manufacturers Association

Kent Perkins, Recreation Vehicle Industry Association, VA [M]
    (Alt. to Bruce A. Hopkins)
    (VL to 550, 551, 552)

Raymond F. Tucker, Consulting Professional Engineer/RADCO, CA [RT]
    (Alt. to Michael L. Zieman)
    (VL to 545, 550, 551, 552)

Ronald D. Weaver, Jr., North Alabama Electrical JATC, AL [L]
    (Alt. to Ronald Michaelis)
    Rep. International Brotherhood of Electrical Workers

Cari Williamette, City of St. Paul, MN [E]
    (Alt. to Ron B. Chilton)
    Rep. International Association of Electrical Inspectors

Eugene W. Wirth, Underwriters Laboratories Inc., WA [RT]
    (Alt. to Thomas R. Lichtenstein)

NFPA Electrical Engineering Division Technical Staff

William Burke, Division Manager
Mark W. Earley, Chief Electrical Engineer
Mark Cloutier, Senior Electrical Engineer
Christopher Coache, Senior Electrical Engineer
Jean A. O’Connor, Electrical Project Specialist/Support
Supervisor
Lee F. Richardson, Senior Electrical Engineer
Richard J. Roux, Senior Electrical Specialist
Jeffrey S. Sargent, Senior Electrical Specialist

Support Staff

Carol Henderson
Mary Warren-Pilson
Kimberly Shea

NFPA Staff Editors

Pamela Nolan
Kim Cervantes

Note: Membership on a committee shall not in and of itself constitute an endorsement of the Association or any document developed by the Committee on which the member serves.

Committee Scope: This Committee shall have primary responsibility for documents on minimizing the risk of electricity as a source of electric shock and as a potential ignition source of fires and explosions. It shall also be responsible for text to minimize the propagation of fire and explosions due to electrical installations.

70-21

NFPA 70
National Electrical Code®
2011 Edition

IMPORTANT NOTE: This NFPA document is made available for use subject to important notices and legal disclaimers. These notices and disclaimers appear in all publications containing this document and may be found under the heading “Important Notices and Disclaimers Concerning NFPA Documents.” They can also be obtained on request from NFPA or viewed at www.nfpa.org/disclaimers.

This 2011 edition includes the following usability features as aids to the user. Changes other than editorial are highlighted with gray shading within sections and with vertical ruling for large blocks of changed or new text and for new tables and changed or new figures. Where one or more complete paragraphs have been deleted, the deletion is indicated by a bullet (•) between the paragraphs that remain. The index now has dictionary-style headers with helpful identifiers at the top of every index page.

ARTICLE 90
Introduction

90.1 Purpose.

(A) Practical Safeguarding. The purpose of this Code is the practical safeguarding of persons and property from hazards arising from the use of electricity.

(B) Adequacy. This Code contains provisions that are considered necessary for safety. Compliance therewith and proper maintenance results in an installation that is essentially free from hazard but not necessarily efficient, convenient, or adequate for good service or future expansion of electrical use.

Informational Note: Hazards often occur because of overloading of wiring systems by methods or usage not in conformity with this Code. This occurs because initial wiring did not provide for increases in the use of electricity. An initial adequate installation and reasonable provisions for system changes provide for future increases in the use of electricity.

(C) Intention. This Code is not intended as a design specification or an instruction manual for untrained persons.

(D) Relation to Other International Standards. The requirements in this Code address the fundamental principles of protection for safety contained in Section 131 of International Electrotechnical Commission Standard 60364-1, Electrical Installations of Buildings.

Informational Note: IEC 60364-1, Section 131, contains fundamental principles of protection for safety that encompass protection against electric shock, protection against thermal effects, protection against overcurrent, protection against fault currents, and protection against overvoltage. All of these potential hazards are addressed by the requirements in this Code.

90.2 Scope.

(A) Covered. This Code covers the installation of electrical conductors, equipment, and raceways; signaling and communications conductors, equipment, and raceways; and optical fiber cables and raceways for the following:

  1. Public and private premises, including buildings, structures, mobile homes, recreational vehicles, and floating buildings
  2. Yards, lots, parking lots, carnivals, and industrial substations
  3. Installations of conductors and equipment that connect to the supply of electricity
  4. Installations used by the electric utility, such as office buildings, warehouses, garages, machine shops, and recreational buildings, that are not an integral part of a generating plant, substation, or control center.

(B) Not Covered. This Code does not cover the following:

  1. Installations in ships, watercraft other than floating buildings, railway rolling stock, aircraft, or automotive vehicles other than mobile homes and recreational vehicles

    Informational Note: Although the scope of this Code indicates that the Code does not cover installations in ships, portions of this Code are incorporated by reference into Title 46, Code of Federal Regulations, Parts 110–113.

  2. Installations underground in mines and self-propelled mobile surface mining machinery and its attendant electrical trailing cable
  3. Installations of railways for generation, transformation, transmission, or distribution of power used exclusively for operation of rolling stock or installations used exclusively for signaling and communications purposes
  4. Installations of communications equipment under the exclusive control of communications utilities located outdoors or in building spaces used exclusively for such installations
  5. Installations under the exclusive control of an electric utility where such installations
    1. Consist of service drops or service laterals, and associated metering, or
    2. Are on property owned or leased by the electric utility for the purpose of communications, metering,70-22 generation, control, transformation, transmission, or distribution of electric energy, or
    3. Are located in legally established easements or rights-of-way, or
    4. Are located by other written agreements either designated by or recognized by public service commissions, utility commissions, or other regulatory agencies having jurisdiction for such installations. These written agreements shall be limited to installations for the purpose of communications, metering generation, control, transformation, transmission, or distribution of electric energy where legally established easements or rights-of-way cannot be obtained. These installations shall be limited to federal lands, native American reservations through the U.S. Department of the Interior Bureau of Indian Affairs, military bases, lands controlled by port authorities and state agencies and departments, and lands owned by railroads.

Informational Note to (4) and (5): Examples of utilities may include those entities that are typically designated or recognized by governmental law or regulation by public service/utility commissions and that install, operate, and maintain electric supply (such as generation, transmission, or distribution systems) or communications systems (such as telephone, CATV, Internet, satellite, or data services). Utilities may be subject to compliance with codes and standards covering their regulated activities as adopted under governmental law or regulation. Additional information can be found through consultation with the appropriate governmental bodies, such as state regulatory commissions, the Federal Energy Regulatory Commission, and the Federal Communications Commission.

(C) Special Permission. The authority having jurisdiction for enforcing this Code may grant exception for the installation of conductors and equipment that are not under the exclusive control of the electric utilities and are used to connect the electric utility supply system to the service conductors of the premises served, provided such installations are outside a building or structure, or terminate inside nearest the point of entrance of the service conductors.

90.3 Code Arrangement. This Code is divided into the introduction and nine chapters, as shown in Figure 90.3. Chapters 1, 2, 3, and 4 apply generally; Chapters 5, 6, and 7 apply to special occupancies, special equipment, or other special conditions. These latter chapters supplement or modify the general rules. Chapters 1 through 4 apply except as amended by Chapters 5, 6, and 7 for the particular conditions.

Chapter 8 covers communications systems and is not subject to the requirements of Chapters 1 through 7 except where the requirements are specifically referenced in Chapter 8.

Chapter 9 consists of tables that are applicable as referenced.

Informative annexes are not part of the requirements of this Code but are included for informational purposes only.

Figure 90.3 Code Arrangement

Figure 90.3 Code Arrangement

90.4 Enforcement. This Code is intended to be suitable for mandatory application by governmental bodies that exercise legal jurisdiction over electrical installations, including signaling and communications systems, and for use by insurance inspectors. The authority having jurisdiction for enforcement of the Code has the responsibility for making interpretations of the rules, for deciding on the approval of equipment and materials, and for granting the special permission contemplated in a number of the rules.

By special permission, the authority having jurisdiction may waive specific requirements in this Code or permit alternative methods where it is assured that equivalent objectives can be achieved by establishing and maintaining effective safety.

This Code may require new products, constructions, or materials that may not yet be available at the time the Code is adopted. In such event, the authority having jurisdiction may permit the use of the products, constructions, or materials that comply with the most recent previous edition of this Code adopted by the jurisdiction.

90.5 Mandatory Rules, Permissive Rules, and Explanatory Material.

(A) Mandatory Rules. Mandatory rules of this Code are those that identify actions that are specifically required or prohibited and are characterized by the use of the terms shall or shall not.

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(B) Permissive Rules. Permissive rules of this Code are those that identify actions that are allowed but not required, are normally used to describe options or alternative methods, and are characterized by the use of the terms shall be permitted or shall not be required.

(C) Explanatory Material. Explanatory material, such as references to other standards, references to related sections of this Code, or information related to a Code rule, is included in this Code in the form of informational notes. Such notes are informational only and are not enforceable as requirements of this Code.

Brackets containing section references to another NFPA document are for informational purposes only and are provided as a guide to indicate the source of the extracted text. These bracketed references immediately follow the extracted text.

Informational Note: The format and language used in this Code follows guidelines established by NFPA and published in the NEC Style Manual. Copies of this manual can be obtained from NFPA.

(D) Informative Annexes. Nonmandatory information relative to the use of the NEC is provided in informative annexes. Informative annexes are not part of the enforceable requirements of the NEC, but are included for information purposes only.

90.6 Formal Interpretations. To promote uniformity of interpretation and application of the provisions of this Code, formal interpretation procedures have been established and are found in the NFPA Regulations Governing Committee Projects.

90.7 Examination of Equipment for Safety. For specific items of equipment and materials referred to in this Code, examinations for safety made under standard conditions provide a basis for approval where the record is made generally available through promulgation by organizations properly equipped and qualified for experimental testing, inspections of the run of goods at factories, and service-value determination through field inspections. This avoids the necessity for repetition of examinations by different examiners, frequently with inadequate facilities for such work, and the confusion that would result from conflicting reports on the suitability of devices and materials examined for a given purpose.

It is the intent of this Code that factory-installed internal wiring or the construction of equipment need not be inspected at the time of installation of the equipment, except to detect alterations or damage, if the equipment has been listed by a qualified electrical testing laboratory that is recognized as having the facilities described in the preceding paragraph and that requires suitability for installation in accordance with this Code.

Informational Note No. 1: See requirements in 110.3.

Informational Note No. 2: Listed is defined in Article 100.

Informational Note No. 3: Informative Annex A contains an informative list of product safety standards for electrical equipment.

90.8 Wiring Planning.

(A) Future Expansion and Convenience. Plans and specifications that provide ample space in raceways, spare raceways, and additional spaces allow for future increases in electric power and communications circuits. Distribution centers located in readily accessible locations provide convenience and safety of operation.

(B) Number of Circuits in Enclosures. It is elsewhere provided in this Code that the number of wires and circuits confined in a single enclosure be varyingly restricted. Limiting the number of circuits in a single enclosure minimizes the effects from a short circuit or ground fault in one circuit.

90.9 Units of Measurement.

(A) Measurement System of Preference. For the purpose of this Code, metric units of measurement are in accordance with the modernized metric system known as the International System of Units (SI).

(B) Dual System of Units. SI units shall appear first, and inch-pound units shall immediately follow in parentheses. Conversion from inch-pound units to SI units shall be based on hard conversion except as provided in 90.9(C).

(C) Permitted Uses of Soft Conversion. The cases given in 90.9(C)(1) through (C)(4) shall not be required to use hard conversion and shall be permitted to use soft conversion.

(1) Trade Sizes. Where the actual measured size of a product is not the same as the nominal size, trade size designators shall be used rather than dimensions. Trade practices shall be followed in all cases.

(2) Extracted Material. Where material is extracted from another standard, the context of the original material shall not be compromised or violated. Any editing of the extracted text shall be confined to making the style consistent with that of the NEC.

(3) Industry Practice. Where industry practice is to express units in inch-pound units, the inclusion of SI units shall not be required.

(4) Safety. Where a negative impact on safety would result, soft conversion shall be used.

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(D) Compliance. Conversion from inch-pound units to SI units shall be permitted to be an approximate conversion. Compliance with the numbers shown in either the SI system or the inch-pound system shall constitute compliance with this Code.

Informational Note No. 1: Hard conversion is considered a change in dimensions or properties of an item into new sizes that might or might not be interchangeable with the sizes used in the original measurement. Soft conversion is considered a direct mathematical conversion and involves a change in the description of an existing measurement but not in the actual dimension.

Informational Note No. 2: SI conversions are based on IEEE/ASTM SI 10-1997, Standard for the Use of the International System of Units (SI): The Modern Metric System.

70-25

Chapter 1 General

ARTICLE 100
Definitions

Scope. This article contains only those definitions essential to the proper application of this Code. It is not intended to include commonly defined general terms or commonly defined technical terms from related codes and standards. In general, only those terms that are used in two or more articles are defined in Article 100. Other definitions are included in the article in which they are used but may be referenced in Article 100.

Part I of this article contains definitions intended to apply wherever the terms are used throughout this Code. Part II contains definitions applicable only to the parts of articles specifically covering installations and equipment operating at over 600 volts, nominal.

I. General

Accessible (as applied to equipment). Admitting close approach; not guarded by locked doors, elevation, or other effective means.

Accessible (as applied to wiring methods). Capable of being removed or exposed without damaging the building structure or finish or not permanently closed in by the structure or finish of the building.

Accessible, Readily (Readily Accessible). Capable of being reached quickly for operation, renewal, or inspections without requiring those to whom ready access is requisite to climb over or remove obstacles or to resort to portable ladders, and so forth.

Ampacity. The maximum current, in amperes, that a conductor can carry continuously under the conditions of use without exceeding its temperature rating.

Appliance. Utilization equipment, generally other than industrial, that is normally built in standardized sizes or types and is installed or connected as a unit to perform one or more functions such as clothes washing, air conditioning, food mixing, deep frying, and so forth.

Approved. Acceptable to the authority having jurisdiction.

Arc-Fault Circuit Interrupter (AFCI). A device intended to provide protection from the effects of arc faults by recognizing characteristics unique to arcing and by functioning to de-energize the circuit when an arc fault is detected.

Askarel. A generic term for a group of nonflammable synthetic chlorinated hydrocarbons used as electrical insulating media. Askarels of various compositional types are used. Under arcing conditions, the gases produced, while consisting predominantly of noncombustible hydrogen chloride, can include varying amounts of combustible gases, depending on the askarel type.

Attachment Plug (Plug Cap) (Plug). A device that, by insertion in a receptacle, establishes a connection between the conductors of the attached flexible cord and the conductors connected permanently to the receptacle.

Authority Having Jurisdiction (AHJ). An organization, office, or individual responsible for enforcing the requirements of a code or standard, or for approving equipment, materials, an installation, or a procedure.

Informational Note: The phrase “authority having jurisdiction,” or its acronym AHJ, is used in NFPA documents in a broad manner, since jurisdictions and approval agencies vary, as do their responsibilities. Where public safety is primary, the authority having jurisdiction may be a federal, state, local, or other regional department or individual such as a fire chief; fire marshal; chief of a fire prevention bureau, labor department, or health department; building official; electrical inspector; or others having statutory authority. For insurance purposes, an insurance inspection department, rating bureau, or other insurance company representative may be the authority having jurisdiction. In many circumstances, the property owner or his or her designated agent assumes the role of the authority having jurisdiction; at government installations, the commanding officer or departmental official may be the authority having jurisdiction.

Automatic. Performing a function without the necessity of human intervention.

Bathroom. An area including a basin with one or more of the following: a toilet, a urinal, a tub, a shower, a bidet, or similar plumbing fixtures.

Bonded (Bonding). Connected to establish electrical continuity and conductivity.

Bonding Conductor or Jumper. A reliable conductor to ensure the required electrical conductivity between metal parts required to be electrically connected.

Bonding Jumper, Equipment. The connection between two or more portions of the equipment grounding conductor.

Bonding Jumper, Main. The connection between the grounded circuit conductor and the equipment grounding conductor at the service.

Bonding Jumper, System. The connection between the grounded circuit conductor and the supply-side bonding

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jumper, or the equipment grounding conductor, or both, at a separately derived system.

Branch Circuit. The circuit conductors between the final overcurrent device protecting the circuit and the outlet(s).

Branch Circuit, Appliance. A branch circuit that supplies energy to one or more outlets to which appliances are to be connected and that has no permanently connected luminaires that are not a part of an appliance.

Branch Circuit, General-Purpose. A branch circuit that supplies two or more receptacles or outlets for lighting and appliances.

Branch Circuit, Individual. A branch circuit that supplies only one utilization equipment.

Branch Circuit, Multiwire. A branch circuit that consists of two or more ungrounded conductors that have a voltage between them, and a grounded conductor that has equal voltage between it and each ungrounded conductor of the circuit and that is connected to the neutral or grounded conductor of the system.

Building. A structure that stands alone or that is cut off from adjoining structures by fire walls with all openings therein protected by approved fire doors.

Cabinet. An enclosure that is designed for either surface mounting or flush mounting and is provided with a frame, mat, or trim in which a swinging door or doors are or can be hung.

Circuit Breaker. A device designed to open and close a circuit by nonautomatic means and to open the circuit automatically on a predetermined overcurrent without damage to itself when properly applied within its rating.

Informational Note: The automatic opening means can be integral, direct acting with the circuit breaker, or remote from the circuit breaker.

Adjustable (as applied to circuit breakers). A qualifying term indicating that the circuit breaker can be set to trip at various values of current, time, or both, within a predetermined range.

Instantaneous Trip (as applied to circuit breakers). A qualifying term indicating that no delay is purposely introduced in the tripping action of the circuit breaker.

Inverse Time (as applied to circuit breakers). A qualifying term indicating that there is purposely introduced a delay in the tripping action of the circuit breaker, which delay decreases as the magnitude of the current increases.

Nonadjustable (as applied to circuit breakers). A qualifying term indicating that the circuit breaker does not have any adjustment to alter the value of current at which it will trip or the time required for its operation.

Setting (of circuit breakers). The value of current, time, or both, at which an adjustable circuit breaker is set to trip.

Clothes Closet. A non-habitable room or space intended primarily for storage of garments and apparel.

Communications Equipment. The electronic equipment that performs the telecommunications operations for the transmission of audio, video, and data, and includes power equipment (e.g., dc converters, inverters, and batteries) and technical support equipment (e.g., computers).

Concealed. Rendered inaccessible by the structure or finish of the building. Wires in concealed raceways are considered concealed, even though they may become accessible by withdrawing them.

Conductor, Bare. A conductor having no covering or electrical insulation whatsoever.

Conductor, Covered. A conductor encased within material of composition or thickness that is not recognized by this Code as electrical insulation.

Conductor, Insulated. A conductor encased within material of composition and thickness that is recognized by this Code as electrical insulation.

Conduit Body. A separate portion of a conduit or tubing system that provides access through a removable cover(s) to the interior of the system at a junction of two or more sections of the system or at a terminal point of the system.

Boxes such as FS and FD or larger cast or sheet metal boxes are not classified as conduit bodies.

Connector, Pressure (Solderless). A device that establishes a connection between two or more conductors or between one or more conductors and a terminal by means of mechanical pressure and without the use of solder.

Continuous Load. A load where the maximum current is expected to continue for 3 hours or more.

Controller. A device or group of devices that serves to govern, in some predetermined manner, the electric power delivered to the apparatus to which it is connected.

Cooking Unit, Counter-Mounted. A cooking appliance designed for mounting in or on a counter and consisting of one or more heating elements, internal wiring, and built-in or mountable controls.

Coordination (Selective). Localization of an overcurrent condition to restrict outages to the circuit or equipment affected, accomplished by the choice of overcurrent protective devices and their ratings or settings.

Copper-Clad Aluminum Conductors. Conductors drawn from a copper-clad aluminum rod with the copper metallurgically bonded to an aluminum core. The copper forms a

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minimum of 10 percent of the cross-sectional area of a solid conductor or each strand of a stranded conductor.

Cutout Box. An enclosure designed for surface mounting that has swinging doors or covers secured directly to and telescoping with the walls of the box proper.

Dead Front. Without live parts exposed to a person on the operating side of the equipment.

Demand Factor. The ratio of the maximum demand of a system, or part of a system, to the total connected load of a system or the part of the system under consideration.

Device. A unit of an electrical system that carries or controls electric energy as its principal function.

Disconnecting Means. A device, or group of devices, or other means by which the conductors of a circuit can be disconnected from their source of supply.

Dusttight. Constructed so that dust will not enter the enclosing case under specified test conditions.

Duty, Continuous. Operation at a substantially constant load for an indefinitely long time.

Duty, Intermittent. Operation for alternate intervals of (1) load and no load; or (2) load and rest; or (3) load, no load, and rest.

Duty, Periodic. Intermittent operation in which the load conditions are regularly recurrent.

Duty, Short-Time. Operation at a substantially constant load for a short and definite, specified time.

Duty, Varying. Operation at loads, and for intervals of time, both of which may be subject to wide variation.

Dwelling, One-Family. A building that consists solely of one dwelling unit.

Dwelling, Two-Family. A building that consists solely of two dwelling units.

Dwelling, Multifamily. A building that contains three or more dwelling units.

Dwelling Unit. A single unit, providing complete and independent living facilities for one or more persons, including permanent provisions for living, sleeping, cooking, and sanitation.

Electric Sign. A fixed, stationary, or portable self-contained, electrically illuminated utilization equipment with words or symbols designed to convey information or attract attention.

Electric Power Production and Distribution Network. Power production, distribution, and utilization equipment and facilities, such as electric utility systems that deliver electric power to the connected loads, that are external to and not controlled by an interactive system.

Enclosed. Surrounded by a case, housing, fence, or wall(s) that prevents persons from accidentally contacting energized parts.

Enclosure. The case or housing of apparatus, or the fence or walls surrounding an installation to prevent personnel from accidentally contacting energized parts or to protect the equipment from physical damage.

Informational Note: See Table 110.28 for examples of enclosure types.

Energized. Electrically connected to, or is, a source of voltage.

Equipment. A general term, including fittings, devices, appliances, luminaires, apparatus, machinery, and the like used as a part of, or in connection with, an electrical installation.

Explosionproof Equipment. Equipment enclosed in a case that is capable of withstanding an explosion of a specified gas or vapor that may occur within it and of preventing the ignition of a specified gas or vapor surrounding the enclosure by sparks, flashes, or explosion of the gas or vapor within, and that operates at such an external temperature that a surrounding flammable atmosphere will not be ignited thereby.

Informational Note: For further information, see ANSI/UL 1203-2006, Explosion-Proof and Dust-Ignition-Proof Electrical Equipment for Use in Hazardous (Classified) Locations.

Exposed (as applied to live parts). Capable of being inadvertently touched or approached nearer than a safe distance by a person. It is applied to parts that are not suitably guarded, isolated, or insulated.

Exposed (as applied to wiring methods). On or attached to the surface or behind panels designed to allow access.

Externally Operable. Capable of being operated without exposing the operator to contact with live parts.

Feeder. All circuit conductors between the service equipment, the source of a separately derived system, or other power supply source and the final branch-circuit overcurrent device.

Festoon Lighting. A string of outdoor lights that is suspended between two points.

Fitting. An accessory such as a locknut, bushing, or other part of a wiring system that is intended primarily to perform a mechanical rather than an electrical function.

Garage. A building or portion of a building in which one or more self-propelled vehicles can be kept for use, sale, storage, rental, repair, exhibition, or demonstration purposes.

Informational Note: For commercial garages, repair and storage, see Article 511.

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Ground. The earth.

Ground Fault. An unintentional, electrically conducting connection between an ungrounded conductor of an electrical circuit and the normally non-current-carrying conductors, metallic enclosures, metallic raceways, metallic equipment, or earth.

Grounded (Grounding). Connected (connecting) to ground or to a conductive body that extends the ground connection.

Grounded, Solidly. Connected to ground without inserting any resistor or impedance device.

Grounded Conductor. A system or circuit conductor that is intentionally grounded.

Ground-Fault Circuit Interrupter (GFCI). A device intended for the protection of personnel that functions to de-energize a circuit or portion thereof within an established period of time when a current to ground exceeds the values established for a Class A device.

Informational Note: Class A ground-fault circuit interrupters trip when the current to ground is 6 mA or higher and do not trip when the current to ground is less than 4 mA. For further information, see UL 943, Standard for Ground-Fault Circuit Interrupters.

Ground-Fault Protection of Equipment. A system intended to provide protection of equipment from damaging line-to-ground fault currents by operating to cause a disconnecting means to open all ungrounded conductors of the faulted circuit. This protection is provided at current levels less than those required to protect conductors from damage through the operation of a supply circuit overcurrent device.

Grounding Conductor, Equipment (EGC). The conductive path(s) installed to connect normally non-current-carrying metal parts of equipment together and to the system grounded conductor or to the grounding electrode conductor, or both.

Informational Note No. 1: It is recognized that the equipment grounding conductor also performs bonding.

Informational Note No. 2: See 250.118 for a list of acceptable equipment grounding conductors.

Grounding Electrode. A conducting object through which a direct connection to earth is established.

Grounding Electrode Conductor. A conductor used to connect the system grounded conductor or the equipment to a grounding electrode or to a point on the grounding electrode system.

Guarded. Covered, shielded, fenced, enclosed, or otherwise protected by means of suitable covers, casings, barriers, rails, screens, mats, or platforms to remove the likelihood of approach or contact by persons or objects to a point of danger.

Guest Room. An accommodation combining living, sleeping, sanitary, and storage facilities within a compartment.

Guest Suite. An accommodation with two or more contiguous rooms comprising a compartment, with or without doors between such rooms, that provides living, sleeping, sanitary, and storage facilities.

Handhole Enclosure. An enclosure for use in underground systems, provided with an open or closed bottom, and sized to allow personnel to reach into, but not enter, for the purpose of installing, operating, or maintaining equipment or wiring or both.

Hoistway. Any shaftway, hatchway, well hole, or other vertical opening or space in which an elevator or dumbwaiter is designed to operate.

Identified (as applied to equipment). Recognizable as suitable for the specific purpose, function, use, environment, application, and so forth, where described in a particular Code requirement.

Informational Note: Some examples of ways to determine suitability of equipment for a specific purpose, environment, or application include investigations by a qualified testing laboratory (listing and labeling), an inspection agency, or other organizations concerned with product evaluation.

In Sight From (Within Sight From, Within Sight). Where this Code specifies that one equipment shall be “in sight from,” “within sight from,” or “within sight of,” and so forth, another equipment, the specified equipment is to be visible and not more than 15 m (50 ft) distant from the other.

Interactive System. An electric power production system that is operating in parallel with and capable of delivering energy to an electric primary source supply system.

Interrupting Rating. The highest current at rated voltage that a device is identified to interrupt under standard test conditions.

Informational Note: Equipment intended to interrupt current at other than fault levels may have its interrupting rating implied in other ratings, such as horsepower or locked rotor current.

Intersystem Bonding Termination. A device that provides a means for connecting bonding conductors for communications systems to the grounding electrode system.

Isolated (as applied to location). Not readily accessible to persons unless special means for access are used.

Kitchen. An area with a sink and permanent provisions for food preparation and cooking.

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Labeled. Equipment or materials to which has been attached a label, symbol, or other identifying mark of an organization that is acceptable to the authority having jurisdiction and concerned with product evaluation, that maintains periodic inspection of production of labeled equipment or materials, and by whose labeling the manufacturer indicates compliance with appropriate standards or performance in a specified manner.

Lighting Outlet. An outlet intended for the direct connection of a lampholder or luminaire.

Listed. Equipment, materials, or services included in a list published by an organization that is acceptable to the authority having jurisdiction and concerned with evaluation of products or services, that maintains periodic inspection of production of listed equipment or materials or periodic evaluation of services, and whose listing states that either the equipment, material, or service meets appropriate designated standards or has been tested and found suitable for a specified purpose.

Informational Note: The means for identifying listed equipment may vary for each organization concerned with product evaluation, some of which do not recognize equipment as listed unless it is also labeled. Use of the system employed by the listing organization allows the authority having jurisdiction to identify a listed product.

Live Parts. Energized conductive components.

Location, Damp. Locations protected from weather and not subject to saturation with water or other liquids but subject to moderate degrees of moisture. Examples of such locations include partially protected locations under canopies, marquees, roofed open porches, and like locations, and interior locations subject to moderate degrees of moisture, such as some basements, some barns, and some cold-storage warehouses.

Location, Dry. A location not normally subject to dampness or wetness. A location classified as dry may be temporarily subject to dampness or wetness, as in the case of a building under construction.

Location, Wet. Installations underground or in concrete slabs or masonry in direct contact with the earth; in locations subject to saturation with water or other liquids, such as vehicle washing areas; and in unprotected locations exposed to weather.

Luminaire. A complete lighting unit consisting of a light source such as a lamp or lamps, together with the parts designed to position the light source and connect it to the power supply. It may also include parts to protect the light source or the ballast or to distribute the light. A lampholder itself is not a luminaire.

Metal-Enclosed Power Switchgear. A switchgear assembly completely enclosed on all sides and top with sheet metal (except for ventilating openings and inspection windows) and containing primary power circuit switching, interrupting devices, or both, with buses and connections. The assembly may include control and auxiliary devices. Access to the interior of the enclosure is provided by doors, removable covers, or both. Metal-enclosed power switchgear is available in non-arc-resistant or arc-resistant constructions.

Motor Control Center. An assembly of one or more enclosed sections having a common power bus and principally containing motor control units.

Multioutlet Assembly. A type of surface, flush, or freestanding raceway designed to hold conductors and receptacles, assembled in the field or at the factory.

Neutral Conductor. The conductor connected to the neutral point of a system that is intended to carry current under normal conditions.

Neutral Point. The common point on a wye-connection in a polyphase system or midpoint on a single-phase, 3-wire system, or midpoint of a single-phase portion of a 3-phase delta system, or a midpoint of a 3-wire, direct-current system.

Informational Note: At the neutral point of the system, the vectorial sum of the nominal voltages from all other phases within the system that utilize the neutral, with respect to the neutral point, is zero potential.

Nonautomatic. Requiring human intervention to perform a function.

Nonlinear Load. A load where the wave shape of the steady-state current does not follow the wave shape of the applied voltage.

Informational Note: Electronic equipment, electronic/electric-discharge lighting, adjustable-speed drive systems, and similar equipment may be nonlinear loads.

Outlet. A point on the wiring system at which current is taken to supply utilization equipment.

Outline Lighting. An arrangement of incandescent lamps, electric-discharge lighting, or other electrically powered light sources to outline or call attention to certain features such as the shape of a building or the decoration of a window.

Overcurrent. Any current in excess of the rated current of equipment or the ampacity of a conductor. It may result from overload, short circuit, or ground fault.

Informational Note: A current in excess of rating may be accommodated by certain equipment and conductors for a given set of conditions. Therefore, the rules for overcurrent protection are specific for particular situations.

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Overcurrent Protective Device, Branch-Circuit. A device capable of providing protection for service, feeder, and branch circuits and equipment over the full range of over-currents between its rated current and its interrupting rating. Branch-circuit overcurrent protective devices are provided with interrupting ratings appropriate for the intended use but no less than 5000 amperes.

Overcurrent Protective Device, Supplementary. A device intended to provide limited overcurrent protection for specific applications and utilization equipment such as luminaires and appliances. This limited protection is in addition to the protection provided in the required branch circuit by the branch-circuit overcurrent protective device.

Overload. Operation of equipment in excess of normal, full-load rating, or of a conductor in excess of rated ampacity that, when it persists for a sufficient length of time, would cause damage or dangerous overheating. A fault, such as a short circuit or ground fault, is not an overload.

Panelboard. A single panel or group of panel units designed for assembly in the form of a single panel, including buses and automatic overcurrent devices, and equipped with or without switches for the control of light, heat, or power circuits; designed to be placed in a cabinet or cutout box placed in or against a wall, partition, or other support; and accessible only from the front.

Plenum. A compartment or chamber to which one or more air ducts are connected and that forms part of the air distribution system.

Power Outlet. An enclosed assembly that may include receptacles, circuit breakers, fuseholders, fused switches, buses, and watt-hour meter mounting means; intended to supply and control power to mobile homes, recreational vehicles, park trailers, or boats or to serve as a means for distributing power required to operate mobile or temporarily installed equipment.

Premises Wiring (System). Interior and exterior wiring, including power, lighting, control, and signal circuit wiring together with all their associated hardware, fittings, and wiring devices, both permanently and temporarily installed. This includes (a) wiring from the service point or power source to the outlets or (b) wiring from and including the power source to the outlets where there is no service point.

Such wiring does not include wiring internal to appliances, luminaires, motors, controllers, motor control centers, and similar equipment.

Qualified Person. One who has skills and knowledge related to the construction and operation of the electrical equipment and installations and has received safety training to recognize and avoid the hazards involved.

Informational Note: Refer to NFPA 70E-2009, Standard for Electrical Safety in the Workplace, for electrical safety training requirements.

Raceway. An enclosed channel of metal or nonmetallic materials designed expressly for holding wires, cables, or busbars, with additional functions as permitted in this Code. Raceways include, but are not limited to, rigid metal conduit, rigid nonmetallic conduit, intermediate metal conduit, liquidtight flexible conduit, flexible metallic tubing, flexible metal conduit, electrical nonmetallic tubing, electrical metallic tubing, underfloor raceways, cellular concrete floor raceways, cellular metal floor raceways, surface raceways, wireways, and busways.

Rainproof. Constructed, protected, or treated so as to prevent rain from interfering with the successful operation of the apparatus under specified test conditions.

Raintight. Constructed or protected so that exposure to a beating rain will not result in the entrance of water under specified test conditions.

Receptacle. A receptacle is a contact device installed at the outlet for the connection of an attachment plug. A single receptacle is a single contact device with no other contact device on the same yoke. A multiple receptacle is two or more contact devices on the same yoke.

Receptacle Outlet. An outlet where one or more receptacles are installed.

Remote-Control Circuit. Any electrical circuit that controls any other circuit through a relay or an equivalent device.

Sealable Equipment. Equipment enclosed in a case or cabinet that is provided with a means of sealing or locking so that live parts cannot be made accessible without opening the enclosure. The equipment may or may not be operable without opening the enclosure.

Separately Derived System. A premises wiring system whose power is derived from a source of electric energy or equipment other than a service. Such systems have no direct connection from circuit conductors of one system to circuit conductors of another system, other than connections through the earth, metal enclosures, metallic raceways, or equipment grounding conductors.

Service. The conductors and equipment for delivering electric energy from the serving utility to the wiring system of the premises served.

Service Cable. Service conductors made up in the form of a cable.

Service Conductors. The conductors from the service point to the service disconnecting means.

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Service Conductors, Overhead. The overhead conductors between the service point and the first point of connection to the service-entrance conductors at the building or other structure.

Service Conductors, Underground. The underground conductors between the service point and the first point of connection to the service-entrance conductors in a terminal box, meter, or other enclosure, inside or outside the building wall.

Informational Note: Where there is no terminal box, meter, or other enclosure, the point of connection is considered to be the point of entrance of the service conductors into the building.

Service Drop. The overhead conductors between the utility electric supply system and the service point.

Service-Entrance Conductors, Overhead System. The service conductors between the terminals of the service equipment and a point usually outside the building, clear of building walls, where joined by tap or splice to the service drop or overhead service conductors.

Service-Entrance Conductors, Underground System. The service conductors between the terminals of the service equipment and the point of connection to the service lateral or underground service conductors.

Informational Note: Where service equipment is located outside the building walls, there may be no service-entrance conductors or they may be entirely outside the building.

Service Equipment. The necessary equipment, usually consisting of a circuit breaker(s) or switch(es) and fuse(s) and their accessories, connected to the load end of service conductors to a building or other structure, or an otherwise designated area, and intended to constitute the main control and cutoff of the supply.

Service Lateral. The underground conductors between the utility electric supply system and the service point.

Service Point. The point of connection between the facilities of the serving utility and the premises wiring.

Informational Note: The service point can be described as the point of demarcation between where the serving utility ends and the premises wiring begins. The serving utility generally specifies the location of the service point based on the conditions of service.

Short-Circuit Current Rating. The prospective symmetrical fault current at a nominal voltage to which an apparatus or system is able to be connected without sustaining damage exceeding defined acceptance criteria.

Show Window. Any window used or designed to be used for the display of goods or advertising material, whether it is fully or partly enclosed or entirely open at the rear and whether or not it has a platform raised higher than the street floor level.

Signaling Circuit. Any electrical circuit that energizes signaling equipment.

Solar Photovoltaic System. The total components and subsystems that, in combination, convert solar energy into electric energy suitable for connection to a utilization load.

Special Permission. The written consent of the authority having jurisdiction.

Structure. That which is built or constructed.

Surge Arrester. A protective device for limiting surge voltages by discharging or bypassing surge current; it also prevents continued flow of follow current while remaining capable of repeating these functions.

Surge-Protective Device (SPD). A protective device for limiting transient voltages by diverting or limiting surge current; it also prevents continued flow of follow current while remaining capable of repeating these functions and is designated as follows:

Type 1: Permanently connected SPDs intended for installation between the secondary of the service transformer and the line side of the service disconnect overcurrent device.

Type 2: Permanently connected SPDs intended for installation on the load side of the service disconnect over-current device, including SPDs located at the branch panel.

Type 3: Point of utilization SPDs.

Type 4: Component SPDs, including discrete components, as well as assemblies.

Informational Note: For further information on Type 1, Type 2, Type 3, and Type 4 SPDs, see UL 1449, Standard for Surge Protective Devices.

Switch, Bypass Isolation. A manually operated device used in conjunction with a transfer switch to provide a means of directly connecting load conductors to a power source and of disconnecting the transfer switch.

Switch, General-Use. A switch intended for use in general distribution and branch circuits. It is rated in amperes, and it is capable of interrupting its rated current at its rated voltage.

Switch, General-Use Snap. A form of general-use switch constructed so that it can be installed in device boxes or on box covers, or otherwise used in conjunction with wiring systems recognized by this Code.

Switch, Isolating. A switch intended for isolating an electrical circuit from the source of power. It has no interrupting rating, and it is intended to be operated only after the circuit has been opened by some other means.

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Switch, Motor-Circuit. A switch rated in horsepower that is capable of interrupting the maximum operating overload current of a motor of the same horsepower rating as the switch at the rated voltage.

Switch, Transfer. An automatic or nonautomatic device for transferring one or more load conductor connections from one power source to another.

Switchboard. A large single panel, frame, or assembly of panels on which are mounted on the face, back, or both, switches, overcurrent and other protective devices, buses, and usually instruments. Switchboards are generally accessible from the rear as well as from the front and are not intended to be installed in cabinets.

Thermal Protector (as applied to motors). A protective device for assembly as an integral part of a motor or motor-compressor that, when properly applied, protects the motor against dangerous overheating due to overload and failure to start.

Informational Note: The thermal protector may consist of one or more sensing elements integral with the motor or motor-compressor and an external control device.

Thermally Protected (as applied to motors). The words Thermally Protected appearing on the nameplate of a motor or motor-compressor indicate that the motor is provided with a thermal protector.

Ungrounded. Not connected to ground or to a conductive body that extends the ground connection.

Uninterruptible Power Supply. A power supply used to provide alternating current power to a load for some period of time in the event of a power failure.

Informational Note: In addition, it may provide a more constant voltage and frequency supply to the load, reducing the effects of voltage and frequency variations.

Utility-Interactive Inverter. An inverter intended for use in parallel with an electric utility to supply common loads that may deliver power to the utility.

Utilization Equipment. Equipment that utilizes electric energy for electronic, electromechanical, chemical, heating, lighting, or similar purposes.

Ventilated. Provided with a means to permit circulation of air sufficient to remove an excess of heat, fumes, or vapors.

Volatile Flammable Liquid. A flammable liquid having a flash point below 38°C (100°F), or a flammable liquid whose temperature is above its flash point, or a Class II combustible liquid that has a vapor pressure not exceeding 276 kPa (40 psia) at 38°C (100°F) and whose temperature is above its flash point.

Voltage (of a circuit). The greatest root-mean-square (rms) (effective) difference of potential between any two conductors of the circuit concerned.

Informational Note: Some systems, such as 3-phase 4-wire, single-phase 3-wire, and 3-wire direct current, may have various circuits of various voltages.

Voltage, Nominal. A nominal value assigned to a circuit or system for the purpose of conveniently designating its voltage class (e.g., 120/240 volts, 480Y/277 volts, 600 volts). The actual voltage at which a circuit operates can vary from the nominal within a range that permits satisfactory operation of equipment.

Informational Note: See ANSI C84.1-2006, Voltage Ratings for Electric Power Systems and Equipment (60 Hz).

Voltage to Ground. For grounded circuits, the voltage between the given conductor and that point or conductor of the circuit that is grounded; for ungrounded circuits, the greatest voltage between the given conductor and any other conductor of the circuit.

Watertight. Constructed so that moisture will not enter the enclosure under specified test conditions.

Weatherproof. Constructed or protected so that exposure to the weather will not interfere with successful operation.

Informational Note: Rainproof, raintight, or watertight equipment can fulfill the requirements for weatherproof where varying weather conditions other than wetness, such as snow, ice, dust, or temperature extremes, are not a factor.

II. Over 600 Volts, Nominal

Whereas the preceding definitions are intended to apply wherever the terms are used throughout this Code, the following definitions are applicable only to parts of the article specifically covering installations and equipment operating at over 600 volts, nominal.

Electronically Actuated Fuse. An overcurrent protective device that generally consists of a control module that provides current sensing, electronically derived time–current characteristics, energy to initiate tripping, and an interrupting module that interrupts current when an overcurrent occurs. Electronically actuated fuses may or may not operate in a current-limiting fashion, depending on the type of control selected.

Fuse. An overcurrent protective device with a circuit-opening fusible part that is heated and severed by the passage of overcurrent through it.

Informational Note: A fuse comprises all the parts that form a unit capable of performing the prescribed functions. It may or may not be the complete device necessary to connect it into an electrical circuit.

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Controlled Vented Power Fuse. A fuse with provision for controlling discharge circuit interruption such that no solid material may be exhausted into the surrounding atmosphere.

Informational Note: The fuse is designed so that discharged gases will not ignite or damage insulation in the path of the discharge or propagate a flashover to or between grounded members or conduction members in the path of the discharge where the distance between the vent and such insulation or conduction members conforms to manufacturer’s recommendations.

Expulsion Fuse Unit (Expulsion Fuse). A vented fuse unit in which the expulsion effect of gases produced by the arc and lining of the fuseholder, either alone or aided by a spring, extinguishes the arc.

Nonvented Power Fuse. A fuse without intentional provision for the escape of arc gases, liquids, or solid particles to the atmosphere during circuit interruption.

Power Fuse Unit. A vented, nonvented, or controlled vented fuse unit in which the arc is extinguished by being drawn through solid material, granular material, or liquid, either alone or aided by a spring.

Vented Power Fuse. A fuse with provision for the escape of arc gases, liquids, or solid particles to the surrounding atmosphere during circuit interruption.

Multiple Fuse. An assembly of two or more single-pole fuses.

Switching Device. A device designed to close, open, or both, one or more electrical circuits.

Circuit Breaker. A switching device capable of making, carrying, and interrupting currents under normal circuit conditions, and also of making, carrying for a specified time, and interrupting currents under specified abnormal circuit conditions, such as those of short circuit.

Cutout. An assembly of a fuse support with either a fuse-holder, fuse carrier, or disconnecting blade. The fuseholder or fuse carrier may include a conducting element (fuse link) or may act as the disconnecting blade by the inclusion of a nonfusible member.

Disconnecting Means. A device, group of devices, or other means whereby the conductors of a circuit can be disconnected from their source of supply.

Disconnecting (or Isolating) Switch (Disconnector, Isolator). A mechanical switching device used for isolating a circuit or equipment from a source of power.

Interrupter Switch. A switch capable of making, carrying, and interrupting specified currents.

Oil Cutout (Oil-Filled Cutout). A cutout in which all or part of the fuse support and its fuse link or disconnecting blade is mounted in oil with complete immersion of the contacts and the fusible portion of the conducting element (fuse link) so that arc interruption by severing of the fuse link or by opening of the contacts will occur under oil.

Oil Switch. A switch having contacts that operate under oil (or askarel or other suitable liquid).

Regulator Bypass Switch. A specific device or combination of devices designed to bypass a regulator.

ARTICLE 110
Requirements for Electrical Installations

I. General

110.1 Scope. This article covers general requirements for the examination and approval, installation and use, access to and spaces about electrical conductors and equipment; enclosures intended for personnel entry; and tunnel installations.

110.2 Approval. The conductors and equipment required or permitted by this Code shall be acceptable only if approved.

Informational Note: See 90.7, Examination of Equipment for Safety, and 110.3, Examination, Identification, Installation, and Use of Equipment. See definitions of Approved, Identified, Labeled, and Listed.

110.3 Examination, Identification, Installation, and Use of Equipment.

(A) Examination. In judging equipment, considerations such as the following shall be evaluated:

  1. Suitability for installation and use in conformity with the provisions of this Code

    Informational Note: Suitability of equipment use may be identified by a description marked on or provided with a product to identify the suitability of the product for a specific purpose, environment, or application. Special conditions of use or other limitations and other pertinent information may be marked on the equipment, included in the product instructions, or included in the appropriate listing and labeling information. Suitability of equipment may be evidenced by listing or labeling.

  2. Mechanical strength and durability, including, for parts designed to enclose and protect other equipment, the adequacy of the protection thus provided
  3. Wire-bending and connection space
  4. Electrical insulation
  5. Heating effects under normal conditions of use and also under abnormal conditions likely to arise in service
  6. Arcing effects
  7. Classification by type, size, voltage, current capacity, and specific use
  8. Other factors that contribute to the practical safeguarding of persons using or likely to come in contact with the equipment
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(B) Installation and Use. Listed or labeled equipment shall be installed and used in accordance with any instructions included in the listing or labeling.

110.4 Voltages. Throughout this Code, the voltage considered shall be that at which the circuit operates. The voltage rating of electrical equipment shall not be less than the nominal voltage of a circuit to which it is connected.

110.5 Conductors. Conductors normally used to carry current shall be of copper unless otherwise provided in this Code. Where the conductor material is not specified, the material and the sizes given in this Code shall apply to copper conductors. Where other materials are used, the size shall be changed accordingly.

Informational Note: For aluminum and copper-clad aluminum conductors, see 310.15.

110.6 Conductor Sizes. Conductor sizes are expressed in American Wire Gage (AWG) or in circular mils.

110.7 Wiring Integrity. Completed wiring installations shall be free from short circuits, ground faults, or any connections to ground other than as required or permitted elsewhere in this Code.

110.8 Wiring Methods. Only wiring methods recognized as suitable are included in this Code. The recognized methods of wiring shall be permitted to be installed in any type of building or occupancy, except as otherwise provided in this Code.

110.9 Interrupting Rating. Equipment intended to interrupt current at fault levels shall have an interrupting rating not less than the nominal circuit voltage and the current that is available at the line terminals of the equipment.

Equipment intended to interrupt current at other than fault levels shall have an interrupting rating at nominal circuit voltage not less than the current that must be interrupted.

110.10 Circuit Impedance, Short-Circuit Current Ratings, and Other Characteristics. The overcurrent protective devices, the total impedance, the equipment short-circuit current ratings, and other characteristics of the circuit to be protected shall be selected and coordinated to permit the circuit protective devices used to clear a fault to do so without extensive damage to the electrical equipment of the circuit. This fault shall be assumed to be either between two or more of the circuit conductors or between any circuit conductor and the equipment grounding conductor(s) permitted in 250.118. Listed equipment applied in accordance with their listing shall be considered to meet the requirements of this section.

110.11 Deteriorating Agents. Unless identified for use in the operating environment, no conductors or equipment shall be located in damp or wet locations; where exposed to gases, fumes, vapors, liquids, or other agents that have a deteriorating effect on the conductors or equipment; or where exposed to excessive temperatures.

Informational Note No. 1: See 300.6 for protection against corrosion.

Informational Note No. 2: Some cleaning and lubricating compounds can cause severe deterioration of many plastic materials used for insulating and structural applications in equipment.

Equipment not identified for outdoor use and equipment identified only for indoor use, such as “dry locations,” “indoor use only,” “damp locations,” or enclosure Types 1, 2, 5, 12, 12K, and/or 13, shall be protected against damage from the weather during construction.

Informational Note No. 3: See Table 110.28 for appropriate enclosure-type designations.

110.12 Mechanical Execution of Work. Electrical equipment shall be installed in a neat and workmanlike manner.

Informational Note: Accepted industry practices are described in ANSI/NECA 1-2006, Standard Practices for Good Workmanship in Electrical Contracting, and other ANSI-approved installation standards.

(A) Unused Openings. Unused openings, other than those intended for the operation of equipment, those intended for mounting purposes, or those permitted as part of the design for listed equipment, shall be closed to afford protection substantially equivalent to the wall of the equipment. Where metallic plugs or plates are used with nonmetallic enclosures, they shall be recessed at least 6 mm (¼ in.) from the outer surface of the enclosure.

(B) Integrity of Electrical Equipment and Connections. Internal parts of electrical equipment, including busbars, wiring terminals, insulators, and other surfaces, shall not be damaged or contaminated by foreign materials such as paint, plaster, cleaners, abrasives, or corrosive residues. There shall be no damaged parts that may adversely affect safe operation or mechanical strength of the equipment such as parts that are broken; bent; cut; or deteriorated by corrosion, chemical action, or overheating.

110.13 Mounting and Cooling of Equipment.

(A) Mounting. Electrical equipment shall be firmly secured to the surface on which it is mounted. Wooden plugs driven into holes in masonry, concrete, plaster, or similar materials shall not be used.

(B) Cooling. Electrical equipment that depends on the natural circulation of air and convection principles for cooling

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of exposed surfaces shall be installed so that room airflow over such surfaces is not prevented by walls or by adjacent installed equipment. For equipment designed for floor mounting, clearance between top surfaces and adjacent surfaces shall be provided to dissipate rising warm air.

Electrical equipment provided with ventilating openings shall be installed so that walls or other obstructions do not prevent the free circulation of air through the equipment.

110.14 Electrical Connections. Because of different characteristics of dissimilar metals, devices such as pressure terminal or pressure splicing connectors and soldering lugs shall be identified for the material of the conductor and shall be properly installed and used. Conductors of dissimilar metals shall not be intermixed in a terminal or splicing connector where physical contact occurs between dissimilar conductors (such as copper and aluminum, copper and copper-clad aluminum, or aluminum and copper-clad aluminum), unless the device is identified for the purpose and conditions of use. Materials such as solder, fluxes, inhibitors, and compounds, where employed, shall be suitable for the use and shall be of a type that will not adversely affect the conductors, installation, or equipment.

Connectors and terminals for conductors more finely stranded than Class B and Class C stranding as shown in Chapter 9, Table 10, shall be identified for the specific conductor class or classes.

Informational Note: Many terminations and equipment are marked with a tightening torque.

(A) Terminals. Connection of conductors to terminal parts shall ensure a thoroughly good connection without damaging the conductors and shall be made by means of pressure connectors (including set-screw type), solder lugs, or splices to flexible leads. Connection by means of wire-binding screws or studs and nuts that have upturned lugs or the equivalent shall be permitted for 10 AWG or smaller conductors.

Terminals for more than one conductor and terminals used to connect aluminum shall be so identified.

(B) Splices. Conductors shall be spliced or joined with splicing devices identified for the use or by brazing, welding, or soldering with a fusible metal or alloy. Soldered splices shall first be spliced or joined so as to be mechanically and electrically secure without solder and then be soldered. All splices and joints and the free ends of conductors shall be covered with an insulation equivalent to that of the conductors or with an insulating device identified for the purpose.

Wire connectors or splicing means installed on conductors for direct burial shall be listed for such use.

(C) Temperature Limitations. The temperature rating associated with the ampacity of a conductor shall be selected and coordinated so as not to exceed the lowest temperature rating of any connected termination, conductor, or device. Conductors with temperature ratings higher than specified for terminations shall be permitted to be used for ampacity adjustment, correction, or both.

(1) Equipment Provisions. The determination of termination provisions of equipment shall be based on 110.14(C)(1)(a) or (C)(1)(b). Unless the equipment is listed and marked otherwise, conductor ampacities used in determining equipment termination provisions shall be based on Table 310.15(B)(16) as appropriately modified by 310.15(B)(6).

(a) Termination provisions of equipment for circuits rated 100 amperes or less, or marked for 14 AWG through 1 AWG conductors, shall be used only for one of the following:

  1. Conductors rated 60°C (140°F).
  2. Conductors with higher temperature ratings, provided the ampacity of such conductors is determined based on the 60°C (140°F) ampacity of the conductor size used.
  3. Conductors with higher temperature ratings if the equipment is listed and identified for use with such conductors.
  4. For motors marked with design letters B, C, or D, conductors having an insulation rating of 75°C (167°F) or higher shall be permitted to be used, provided the ampacity of such conductors does not exceed the 75°C (167°F) ampacity.

(b) Termination provisions of equipment for circuits rated over 100 amperes, or marked for conductors larger than 1 AWG, shall be used only for one of the following:

  1. Conductors rated 75°C (167°F)
  2. Conductors with higher temperature ratings, provided the ampacity of such conductors does not exceed the 75°C (167°F) ampacity of the conductor size used, or up to their ampacity if the equipment is listed and identified for use with such conductors

(2) Separate Connector Provisions. Separately installed pressure connectors shall be used with conductors at the ampacities not exceeding the ampacity at the listed and identified temperature rating of the connector.

Informational Note: With respect to 110.14(C)(1) and (C)(2), equipment markings or listing information may additionally restrict the sizing and temperature ratings of connected conductors.

110.15 High-Leg Marking. On a 4-wire, delta-connected system where the midpoint of one phase winding is grounded, only the conductor or busbar having the higher phase voltage to ground shall be durably and permanently marked by an outer finish that is orange in color or by other

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effective means. Such identification shall be placed at each point on the system where a connection is made if the grounded conductor is also present.

110.16 Arc-Flash Hazard Warning. Electrical equipment, such as switchboards, panelboards, industrial control panels, meter socket enclosures, and motor control centers, that are in other than dwelling units, and are likely to require examination, adjustment, servicing, or maintenance while energized shall be field marked to warn qualified persons of potential electric arc flash hazards. The marking shall be located so as to be clearly visible to qualified persons before examination, adjustment, servicing, or maintenance of the equipment.

Informational Note No. 1: NFPA 70E-2009, Standard for Electrical Safety in the Workplace, provides assistance in determining severity of potential exposure, planning safe work practices, and selecting personal protective equipment.

Informational Note No. 2: ANSI Z535.4-1998, Product Safety Signs and Labels, provides guidelines for the design of safety signs and labels for application to products.

110.18 Arcing Parts. Parts of electrical equipment that in ordinary operation produce arcs, sparks, flames, or molten metal shall be enclosed or separated and isolated from all combustible material.

Informational Note: For hazardous (classified) locations, see Articles 500 through 517. For motors, see 430.14.

110.19 Light and Power from Railway Conductors. Circuits for lighting and power shall not be connected to any system that contains trolley wires with a ground return.

Exception: Such circuit connections shall be permitted in car houses, power houses, or passenger and freight stations operated in connection with electric railways.

110.21 Marking. The manufacturer’s name, trademark, or other descriptive marking by which the organization responsible for the product can be identified shall be placed on all electrical equipment. Other markings that indicate voltage, current, wattage, or other ratings shall be provided as specified elsewhere in this Code. The marking shall be of sufficient durability to withstand the environment involved.

110.22 Identification of Disconnecting Means.

(A) General. Each disconnecting means shall be legibly marked to indicate its purpose unless located and arranged so the purpose is evident. The marking shall be of sufficient durability to withstand the environment involved.

(B) Engineered Series Combination Systems. Equipment enclosures for circuit breakers or fuses applied in compliance with series combination ratings selected under engineering supervision in accordance with 240.86(A) shall be legibly marked in the field as directed by the engineer to indicate the equipment has been applied with a series combination rating. The marking shall be readily visible and state the following:

CAUTION — ENGINEERED SERIES COMBINATION SYSTEM RATED _______ AMPERES. IDENTIFIED REPLACEMENT COMPONENTS REQUIRED.

(C) Tested Series Combination Systems. Equipment enclosures for circuit breakers or fuses applied in compliance with the series combination ratings marked on the equipment by the manufacturer in accordance with 240.86(B) shall be legibly marked in the field to indicate the equipment has been applied with a series combination rating. The marking shall be readily visible and state the following:

CAUTION — SERIES COMBINATION SYSTEM RATED _______ AMPERES. IDENTIFIED REPLACEMENT COMPONENTS REQUIRED.

110.23 Current Transformers. Unused current transformers associated with potentially energized circuits shall be short-circuited.

110.24 Available Fault Current.

(A) Field Marking. Service equipment in other than dwelling units shall be legibly marked in the field with the maximum available fault current. The field marking(s) shall include the date the fault current calculation was performed and be of sufficient durability to withstand the environment involved.

(B) Modifications. When modifications to the electrical installation occur that affect the maximum available fault current at the service, the maximum available fault current shall be verified or recalculated as necessary to ensure the service equipment ratings are sufficient for the maximum available fault current at the line terminals of the equipment. The required field marking(s) in 110.24(A) shall be adjusted to reflect the new level of maximum available fault current.

Exception: The field marking requirements in 110.24(A) and 110.24(B) shall not be required in industrial installations where conditions of maintenance and supervision ensure that only qualified persons service the equipment.

II. 600 Volts, Nominal, or Less

110.26 Spaces About Electrical Equipment. Access and working space shall be provided and maintained about all electrical equipment to permit ready and safe operation and maintenance of such equipment.

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(A) Working Space. Working space for equipment operating at 600 volts, nominal, or less to ground and likely to require examination, adjustment, servicing, or maintenance while energized shall comply with the dimensions of 110.26(A)(1), (A)(2), and (A)(3) or as required or permitted elsewhere in this Code.

(1) Depth of Working Space. The depth of the working space in the direction of live parts shall not be less than that specified in Table 110.26(A)(1) unless the requirements of 110.26(A)(1)(a), (A)(1)(b), or (A)(1)(c) are met. Distances shall be measured from the exposed live parts or from the enclosure or opening if the live parts are enclosed.

Table 110.26(A)(1) Working Spaces
Nominal Voltage to Ground Minimum Clear Distance
Condition 1 Condition 2 Condition 3
    0–150 914 mm (3 ft) 914 mm (3 ft) 914 mm (3 ft)
151–600 914 mm (3 ft) 1.07 m (3 ft 6 in.) 1.22 m (4 ft)
Note: Where the conditions are as follows:
Condition 1 — Exposed live parts on one side of the working space and no live or grounded parts on the other side of the working space, or exposed live parts on both sides of the working space that are effectively guarded by insulating materials.
Condition 2 — Exposed live parts on one side of the working space and grounded parts on the other side of the working space. Concrete, brick, or tile walls shall be considered as grounded.
Condition 3 — Exposed live parts on both sides of the working space.

(a) Dead-Front Assemblies. Working space shall not be required in the back or sides of assemblies, such as dead-front switchboards or motor control centers, where all connections and all renewable or adjustable parts, such as fuses or switches, are accessible from locations other than the back or sides. Where rear access is required to work on nonelectrical parts on the back of enclosed equipment, a minimum horizontal working space of 762 mm (30 in.) shall be provided.

(b) Low Voltage. By special permission, smaller working spaces shall be permitted where all exposed live parts operate at not greater than 30 volts rms, 42 volts peak, or 60 volts dc.

(c) Existing Buildings. In existing buildings where electrical equipment is being replaced, Condition 2 working clearance shall be permitted between dead-front switchboards, panelboards, or motor control centers located across the aisle from each other where conditions of maintenance and supervision ensure that written procedures have been adopted to prohibit equipment on both sides of the aisle from being open at the same time and qualified persons who are authorized will service the installation.

(2) Width of Working Space. The width of the working space in front of the electrical equipment shall be the width of the equipment or 762 mm (30 in.), whichever is greater. In all cases, the work space shall permit at least a 90 degree opening of equipment doors or hinged panels.

(3) Height of Working Space. The work space shall be clear and extend from the grade, floor, or platform to a height of 2.0 m (6½ ft) or the height of the equipment, whichever is greater. Within the height requirements of this section, other equipment that is associated with the electrical installation and is located above or below the electrical equipment shall be permitted to extend not more than 150 mm (6 in.) beyond the front of the electrical equipment.

Exception No. 1: In existing dwelling units, service, equipment or panelboards that do not exceed 200 amperes shall be permitted in spaces where the height of the working space is less than 2.0 m (6½ ft).

Exception No. 2: Meters that are installed in meter sockets shall be permitted to extend beyond the other equipment. The meter socket shall be required to follow the rules of this section.

(B) Clear Spaces. Working space required by this section shall not be used for storage. When normally enclosed live parts are exposed for inspection or servicing, the working space, if in a passageway or general open space, shall be suitably guarded.

(C) Entrance to and Egress from Working Space.

(1) Minimum Required. At least one entrance of sufficient area shall be provided to give access to and egress from working space about electrical equipment.

(2) Large Equipment. For equipment rated 1200 amperes or more and over 1.8 m (6 ft) wide that contains overcurrent devices, switching devices, or control devices, there shall be one entrance to and egress from the required working space not less than 610 mm (24 in.) wide and 2.0 m (6½ ft) high at each end of the working space.

A single entrance to and egress from the required working space shall be permitted where either of the conditions in 110.26(C)(2)(a) or (C)(2)(b) is met.

(a) Unobstructed Egress. Where the location permits a continuous and unobstructed way of egress travel, a single entrance to the working space shall be permitted.

(b) Extra Working Space. Where the depth of the working space is twice that required by 110.26(A)(1), a single entrance shall be permitted. It shall be located such that the distance from the equipment to the nearest edge of the entrance is not less than the minimum clear distance specified in Table 110.26(A)(1) for equipment operating at that voltage and in that condition.

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(3) Personnel Doors. Where equipment rated 1200 A or more that contains overcurrent devices, switching devices, or control devices is installed and there is a personnel door(s) intended for entrance to and egress from the working space less than 7.6 m (25 ft) from the nearest edge of the working space, the door(s) shall open in the direction of egress and be equipped with panic bars, pressure plates, or other devices that are normally latched but open under simple pressure.

(D) Illumination. Illumination shall be provided for all working spaces about service equipment, switchboards, panelboards, or motor control centers installed indoors and shall not be controlled by automatic means only. Additional lighting outlets shall not be required where the work space is illuminated by an adjacent light source or as permitted by 210.70(A)(1), Exception No. 1, for switched receptacles.

(E) Dedicated Equipment Space. All switchboards, panelboards, and motor control centers shall be located in dedicated spaces and protected from damage.

Exception: Control equipment that by its very nature or because of other rules of the Code must be adjacent to or within sight of its operating machinery shall be permitted in those locations.

(1) Indoor. Indoor installations shall comply with 110.26(E)(1)(a) through (E)(1)(d).

(a) Dedicated Electrical Space. The space equal to the width and depth of the equipment and extending from the floor to a height of 1.8 m (6 ft) above the equipment or to the structural ceiling, whichever is lower, shall be dedicated to the electrical installation. No piping, ducts, leak protection apparatus, or other equipment foreign to the electrical installation shall be located in this zone.

Exception: Suspended ceilings with removable panels shall be permitted within the 1.8-m (6-ft) zone.

(b) Foreign Systems. The area above the dedicated space required by 110.26(E)(1)(a) shall be permitted to contain foreign systems, provided protection is installed to avoid damage to the electrical equipment from condensation, leaks, or breaks in such foreign systems.

(c) Sprinkler Protection. Sprinkler protection shall be permitted for the dedicated space where the piping complies with this section.

(d) Suspended Ceilings. A dropped, suspended, or similar ceiling that does not add strength to the building structure shall not be considered a structural ceiling.

(2) Outdoor. Outdoor electrical equipment shall be installed in suitable enclosures and shall be protected from accidental contact by unauthorized personnel, or by vehicular traffic, or by accidental spillage or leakage from piping systems. The working clearance space shall include the zone described in 110.26(A). No architectural appurtenance or other equipment shall be located in this zone.

(F) Locked Electrical Equipment Rooms or Enclosures. Electrical equipment rooms or enclosures housing electrical apparatus that are controlled by a lock(s) shall be considered accessible to qualified persons.

110.27 Guarding of Live Parts.

(A) Live Parts Guarded Against Accidental Contact. Except as elsewhere required or permitted by this Code, live parts of electrical equipment operating at 50 volts or more shall be guarded against accidental contact by approved enclosures or by any of the following means:

  1. By location in a room, vault, or similar enclosure that is accessible only to qualified persons.
  2. By suitable permanent, substantial partitions or screens arranged so that only qualified persons have access to the space within reach of the live parts. Any openings in such partitions or screens shall be sized and located so that persons are not likely to come into accidental contact with the live parts or to bring conducting objects into contact with them.
  3. By location on a suitable balcony, gallery, or platform elevated and arranged so as to exclude unqualified persons.
  4. By elevation of 2.5 m (8 ft) or more above the floor or other working surface.

(B) Prevent Physical Damage. In locations where electrical equipment is likely to be exposed to physical damage, enclosures or guards shall be so arranged and of such strength as to prevent such damage.

(C) Warning Signs. Entrances to rooms and other guarded locations that contain exposed live parts shall be marked with conspicuous warning signs forbidding unqualified persons to enter.

Informational Note: For motors, see 430.232 and 430.233. For over 600 volts, see 110.34.

110.28 Enclosure Types. Enclosures (other than surrounding fences or walls) of switchboards, panelboards, industrial control panels, motor control centers, meter sockets, enclosed switches, transfer switches, power outlets, circuit breakers, adjustable-speed drive systems, pullout switches, portable power distribution equipment, termination boxes, general-purpose transformers, fire pump controllers, fire pump motors, and motor controllers, rated not over 600 volts nominal and intended for such locations, shall be marked with an enclosure-type number as shown in Table 110.28.

Table 110.28 shall be used for selecting these enclosures for use in specific locations other than hazardous

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(classified) locations. The enclosures are not intended to protect against conditions such as condensation, icing, corrosion, or contamination that may occur within the enclosure or enter via the conduit or unsealed openings.

III. Over 600 Volts, Nominal

110.30 General. Conductors and equipment used on circuits over 600 volts, nominal, shall comply with Part I of this article and with 110.30 through 110.40, which supplement or modify Part I. In no case shall the provisions of this part apply to equipment on the supply side of the service point.

110.31 Enclosure for Electrical Installations. Electrical installations in a vault, room, or closet or in an area surrounded by a wall, screen, or fence, access to which is controlled by a lock(s) or other approved means, shall be considered to be accessible to qualified persons only. The type of enclosure used in a given case shall be designed and constructed according to the nature and degree of the hazard(s) associated with the installation.

For installations other than equipment as described in 110.31(D), a wall, screen, or fence shall be used to enclose an outdoor electrical installation to deter access by persons who are not qualified. A fence shall not be less than 2.1 m (7 ft) in height or a combination of 1.8 m (6 ft) or more of fence fabric and a 300-mm (1-ft) or more extension utilizing three or more strands of barbed wire or equivalent. The distance from the fence to live parts shall be not less than given in Table 110.31.

Table 110.31 Minimum Distance from Fence to Live Parts
Nominal Voltage Minimum Distance to Live Parts
m ft
601 – 13,799 3.05 10
13,800 – 230,000 4.57 15
Over 230,000 5.49 18
Note: For clearances of conductors for specific system voltages and typical BIL ratings, see ANSI C2-2007, National Electrical Safety Code.

Informational Note: See Article 450 for construction requirements for transformer vaults.

(A) Electrical Vaults. Where an electrical vault is required or specified for conductors and equipment operating at over 600 volts, nominal, the following shall apply.

(1) Walls and Roof. The walls and roof shall be constructed of materials that have adequate structural strength for the conditions, with a minimum fire rating of 3 hours. For the purpose of this section, studs and wallboard construction shall not be permitted.

(2) Floors. The floors of vaults in contact with the earth shall be of concrete that is not less than 102 mm (4 in.) thick, but where the vault is constructed with a vacant space or other stories below it, the floor shall have adequate structural strength for the load imposed on it and a minimum fire resistance of 3 hours.

(3) Doors. Each doorway leading into a vault from the building interior shall be provided with a tight-fitting door that has a minimum fire rating of 3 hours. The authority having jurisdiction shall be permitted to require such a door for an exterior wall opening where conditions warrant.

Exception to (1), (2), and (3): Where the vault is protected with automatic sprinkler, water spray, carbon dioxide, or halon, construction with a 1-hour rating shall be permitted.

(4) Locks. Doors shall be equipped with locks, and doors shall be kept locked, with access allowed only to qualified persons. Personnel doors shall swing out and be equipped with panic bars, pressure plates, or other devices that are normally latched but that open under simple pressure.

(5) Transformers. Where a transformer is installed in a vault as required by Article 450, the vault shall be constructed in accordance with the requirements of Part III of Article 450.

Informational Note No. 1: For additional information, see ANSI/ASTM E119-1995, Method for Fire Tests of Building Construction and Materials, NFPA 251-2006, Standard Methods of Tests of Fire Resistance of Building Construction and Materials, and NFPA 80-2010, Standard for Fire Doors and Other Opening Protectives.

Informational Note No. 2: A typical 3-hour construction is 150 mm (6 in.) thick reinforced concrete.

(B) Indoor Installations.

(1) In Places Accessible to Unqualified Persons. Indoor electrical installations that are accessible to unqualified persons shall be made with metal-enclosed equipment. Metal-enclosed switchgear, unit substations, transformers, pull boxes, connection boxes, and other similar associated equipment shall be marked with appropriate caution signs. Openings in ventilated dry-type transformers or similar openings in other equipment shall be designed so that foreign objects inserted through these openings are deflected from energized parts.

(2) In Places Accessible to Qualified Persons Only. Indoor electrical installations considered accessible only to qualified persons in accordance with this section shall comply with 110.34, 110.36, and 490.24.

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Table 110.28 Enclosure Selection
Provides a Degree of Protection
Against the Following
Environmental Conditions
For Outdoor Use
Enclosure-Type Number
3 3R 3S 3X 3RX 3SX 4 4X 6 6P
Incidental contact
   with the enclosed equipment
X X X X X X X X X X
Rain, snow, and sleet X X X X X X X X X X
Sleet* X X
Windblown dust X X X X X X X X
Hosedown X X X X
Corrosive agents X X X X X
Temporary submersion X X
Prolonged submersion X
Provides a Degree of Protection
Against the Following
Environmental Conditions
For Indoor Use
Enclosure-Type Number
1 2 4 4X 5 6 6P 12 12K 13
Incidental contact with the enclosed equipment X X X X X X X X X X
Falling dirt X X X X X X X X X X
Falling liquids and light splashing X X X X X X X X X
Circulating dust, lint, fibers, and flyings X X X X X X X
Settling airborne dust, lint, fibers, and flyings X X X X X X X X
Hosedown and splashing water X X X X
Oil and coolant seepage X X X
Oil or coolant spraying and splashing X
Corrosive agents X X
Temporary submersion X X
Prolonged submersion X
*Mechanism shall be operable when ice covered.
Informational Note No. 1: The term raintight is typically used in conjunction with Enclosure Types 3, 3S, 3SX, 3X, 4, 4X, 6, and 6P. The term rainproof is typically used in conjunction with Enclosure Types 3R, and 3RX. The term watertight is typically used in conjunction with Enclosure Types 4, 4X, 6, 6P. The term driptight is typically used in conjunction with Enclosure Types 2, 5, 12, 12K, and 13. The term dusttight is typically used in conjunction with Enclosure Types 3, 3S, 3SX, 3X, 5, 12, 12K. and 13.
Informational Note No. 2: Ingress protection (IP) ratings may be found in ANSI/NEMA 60529, Degrees of Protection Provided by Enclosures. IP ratings are not a substitute for Enclosure Type ratings.
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(C) Outdoor Installations.

(1) In Places Accessible to Unqualified Persons. Outdoor electrical installations that are open to unqualified persons shall comply with Parts I, II, and III of Article 225.

(2) In Places Accessible to Qualified Persons Only. Outdoor electrical installations that have exposed live parts shall be accessible to qualified persons only in accordance with the first paragraph of this section and shall comply with 110.34, 110.36, and 490.24.

(D) Enclosed Equipment Accessible to Unqualified Persons. Ventilating or similar openings in equipment shall be designed such that foreign objects inserted through these openings are deflected from energized parts. Where exposed to physical damage from vehicular traffic, suitable guards shall be provided. Nonmetallic or metal-enclosed equipment located outdoors and accessible to the general public shall be designed such that exposed nuts or bolts cannot be readily removed, permitting access to live parts. Where nonmetallic or metal-enclosed equipment is accessible to the general public and the bottom of the enclosure is less than 2.5 m (8 ft) above the floor or grade level, the enclosure door or hinged cover shall be kept locked. Doors and covers of enclosures used solely as pull boxes, splice boxes, or junction boxes shall be locked, bolted, or screwed on. Underground box covers that weigh over 45.4 kg (100 lb) shall be considered as meeting this requirement.

110.32 Work Space About Equipment. Sufficient space shall be provided and maintained about electrical equipment to permit ready and safe operation and maintenance of such equipment. Where energized parts are exposed, the minimum clear work space shall be not less than 2.0 m (6½ ft) high (measured vertically from the floor or platform) or not less than 914 mm (3 ft) wide (measured parallel to the equipment). The depth shall be as required in 110.34(A). In all cases, the work space shall permit at least a 90 degree opening of doors or hinged panels.

110.33 Entrance to Enclosures and Access to Working Space.

(A) Entrance. At least one entrance to enclosures for electrical installations as described in 110.31 not less than 610 mm (24 in.) wide and 2.0 m (6½ ft) high shall be provided to give access to the working space about electrical equipment.

(1) Large Equipment. On switchboard and control panels exceeding 1.8 m (6 ft) in width, there shall be one entrance at each end of the equipment. A single entrance to the required working space shall be permitted where either of the conditions in 110.33(A)(1)(a) or (A)(1)(b) is met.

(a) Unobstructed Exit. Where the location permits a continuous and unobstructed way of exit travel, a single entrance to the working space shall be permitted.

(b) Extra Working Space. Where the depth of the working space is twice that required by 110.34(A), a single entrance shall be permitted. It shall be located so that the distance from the equipment to the nearest edge of the entrance is not less than the minimum clear distance specified in Table 110.34(A) for equipment operating at that voltage and in that condition.

(2) Guarding. Where bare energized parts at any voltage or insulated energized parts above 600 volts, nominal, to ground are located adjacent to such entrance, they shall be suitably guarded.

(3) Personnel Doors. Where there is a personnel door(s) intended for entrance to and egress from the working space less than 7.6 m (25 ft) from the nearest edge of the working space, the door(s) shall open in the direction of egress and be equipped with panic bars, pressure plates, or other devices that are normally latched but open under simple pressure.

(B) Access. Permanent ladders or stairways shall be provided to give safe access to the working space around electrical equipment installed on platforms, balconies, or mezzanine floors or in attic or roof rooms or spaces.

110.34 Work Space and Guarding.

(A) Working Space. Except as elsewhere required or permitted in this Code, equipment likely to require examination, adjustment, servicing, or maintenance while energized shall have clear working space in the direction of access to live parts of the electrical equipment and shall be not less than specified in Table 110.34(A). Distances shall be measured from the live parts, if such are exposed, or from the enclosure front or opening if such are enclosed.

Exception: Working space shall not be required in back of equipment such as dead-front switchboards or control assemblies where there are no renewable or adjustable parts (such as fuses or switches) on the back and where all connections are accessible from locations other than the back. Where rear access is required to work on nonelectrical parts on the back of enclosed equipment, a minimum working space of 762 mm (30 in.) horizontally shall be provided.

(B) Separation from Low-Voltage Equipment. Where switches, cutouts, or other equipment operating at 600 volts, nominal, or less are installed in a vault, room, or enclosure where there are exposed live parts or exposed wiring operating at over 600 volts, nominal, the high-voltage equipment shall be effectively separated from the space occupied by the low-voltage equipment by a suitable partition, fence, or screen.

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Table 110.34(A) Minimum Depth of Clear Working Space at Electrical Equipment
Nominal Voltage to Ground Minimum Clear Distance
Condition 1 Condition 2 Condition 3
601–2500 V 900 mm (3 ft) 1.2 m (4 ft) 1.5 m (5 ft)
2501–9000 V 1.2 m (4 ft) 1.5 m (5 ft) 1.8 m (6 ft)
9001–25,000 V 1.5 m (5 ft) 1.8 m (6 ft) 2.8 m (9 ft)
25,001 V–75 kV 1.8 m (6 ft) 2.5 m (8 ft)   3.0 m (10 ft)
Above 75 kV 2.5 m (8 ft)   3.0 m (10 ft)   3.7 m (12 ft)
Note: Where the conditions are as follows:
Condition 1 — Exposed live parts on one side of the working space and no live or grounded parts on the other side of the working space, or exposed live parts on both sides of the working space that are effectively guarded by insulating materials.
Condition 2 — Exposed live parts on one side of the working space and grounded parts on the other side of the working space. Concrete, brick, or tile walls shall be considered as grounded.
Condition 3 — Exposed live parts on both sides of the working space.

Exception: Switches or other equipment operating at 600 volts, nominal, or less and serving only equipment within the high-voltage vault, room, or enclosure shall be permitted to be installed in the high-voltage vault, room, or enclosure without a partition, fence, or screen if accessible to qualified persons only.

(C) Locked Rooms or Enclosures. The entrance to all buildings, vaults, rooms, or enclosures containing exposed live parts or exposed conductors operating at over 600 volts, nominal, shall be kept locked unless such entrances are under the observation of a qualified person at all times.

Where the voltage exceeds 600 volts, nominal, permanent and conspicuous warning signs shall be provided, reading as follows:

DANGER — HIGH VOLTAGE — KEEP OUT

(D) Illumination. Illumination shall be provided for all working spaces about electrical equipment. The lighting outlets shall be arranged so that persons changing lamps or making repairs on the lighting system are not endangered by live parts or other equipment.

The points of control shall be located so that persons are not likely to come in contact with any live part or moving part of the equipment while turning on the lights.

(E) Elevation of Unguarded Live Parts. Unguarded live parts above working space shall be maintained at elevations not less than required by Table 110.34(E).

(F) Protection of Service Equipment, Metal-Enclosed Power Switchgear, and Industrial Control Assemblies. Pipes or ducts foreign to the electrical installation and requiring periodic maintenance or whose malfunction would endanger the operation of the electrical system shall not be located in the vicinity of the service equipment, metal-enclosed power switchgear, or industrial control assemblies. Protection shall be provided where necessary to avoid damage from condensation leaks and breaks in such foreign systems. Piping and other facilities shall not be considered foreign if provided for fire protection of the electrical installation.

Table 110.34(E) Elevation of Unguarded Live Parts Above Working Space
Nominal Voltage Between Phases Elevation
m ft
601–7500 V 2.8 9
7501–35,000 V 2.9 9 ft 6 in.
Over 35 kV 2.9 m + 9.5 mm/kV
above 35
9 ft 6 in. +
0.37 in./kV
above 35

110.36 Circuit Conductors. Circuit conductors shall be permitted to be installed in raceways; in cable trays; as metal-clad cable, as bare wire, cable, and busbars; or as Type MV cables or conductors as provided in 300.37, 300.39, 300.40, and 300.50. Bare live conductors shall comply with 490.24.

Insulators, together with their mounting and conductor attachments, where used as supports for wires, single-conductor cables, or busbars, shall be capable of safely withstanding the maximum magnetic forces that would prevail if two or more conductors of a circuit were subjected to short-circuit current.

Exposed runs of insulated wires and cables that have a bare lead sheath or a braided outer covering shall be supported in a manner designed to prevent physical damage to the braid or sheath. Supports for lead-covered cables shall be designed to prevent electrolysis of the sheath.

110.40 Temperature Limitations at Terminations. Conductors shall be permitted to be terminated based on the 90°C (194°F) temperature rating and ampacity as given in Table 310.60(C)(67) through Table 310.60(C)(86), unless otherwise identified.

IV. Tunnel Installations over 600 Volts, Nominal

110.51 General.

(A) Covered. The provisions of this part shall apply to the installation and use of high-voltage power distribution and utilization equipment that is portable, mobile, or both, such as substations, trailers, cars, mobile shovels, draglines, hoists, drills, dredges, compressors, pumps, conveyors, underground excavators, and the like.

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(B) Other Articles. The requirements of this part shall be additional to, or amendatory of, those prescribed in Articles 100 through 490 of this Code.

(C) Protection Against Physical Damage. Conductors and cables in tunnels shall be located above the tunnel floor and so placed or guarded to protect them from physical damage.

110.52 Overcurrent Protection. Motor-operated equipment shall be protected from overcurrent in accordance with Parts III, IV, and V of Article 430. Transformers shall be protected from overcurrent in accordance with 450.3.

110.53 Conductors. High-voltage conductors in tunnels shall be installed in metal conduit or other metal raceway, Type MC cable, or other approved multiconductor cable. Multiconductor portable cable shall be permitted to supply mobile equipment.

110.54 Bonding and Equipment Grounding Conductors.

(A) Grounded and Bonded. All non-current-carrying metal parts of electrical equipment and all metal raceways and cable sheaths shall be solidly grounded and bonded to all metal pipes and rails at the portal and at intervals not exceeding 300 m (1000 ft) throughout the tunnel.

(B) Equipment Grounding Conductors. An equipment grounding conductor shall be run with circuit conductors inside the metal raceway or inside the multiconductor cable jacket. The equipment grounding conductor shall be permitted to be insulated or bare.

110.55 Transformers, Switches, and Electrical Equipment. All transformers, switches, motor controllers, motors, rectifiers, and other equipment installed belowground shall be protected from physical damage by location or guarding.

110.56 Energized Parts. Bare terminals of transformers, switches, motor controllers, and other equipment shall be enclosed to prevent accidental contact with energized parts.

110.57 Ventilation System Controls. Electrical controls for the ventilation system shall be arranged so that the airflow can be reversed.

110.58 Disconnecting Means. A switch or circuit breaker that simultaneously opens all ungrounded conductors of the circuit shall be installed within sight of each transformer or motor location for disconnecting the transformer or motor. The switch or circuit breaker for a transformer shall have an ampere rating not less than the ampacity of the transformer supply conductors. The switch or circuit breaker for a motor shall comply with the applicable requirements of Article 430.

110.59 Enclosures. Enclosures for use in tunnels shall be dripproof, weatherproof, or submersible as required by the environmental conditions. Switch or contactor enclosures shall not be used as junction boxes or as raceways for conductors feeding through or tapping off to other switches, unless the enclosures comply with 312.8.

V. Manholes and Other Electrical Enclosures Intended for Personnel Entry, All Voltages

110.70 General. Electrical enclosures intended for personnel entry and specifically fabricated for this purpose shall be of sufficient size to provide safe work space about electrical equipment with live parts that is likely to require examination, adjustment, servicing, or maintenance while energized. Such enclosures shall have sufficient size to permit ready installation or withdrawal of the conductors employed without damage to the conductors or to their insulation. They shall comply with the provisions of this part.

Exception: Where electrical enclosures covered by Part V of this article are part of an industrial wiring system operating under conditions of maintenance and supervision that ensure that only qualified persons monitor and supervise the system, they shall be permitted to be designed and installed in accordance with appropriate engineering practice. If required by the authority having jurisdiction, design documentation shall be provided.

110.71 Strength. Manholes, vaults, and their means of access shall be designed under qualified engineering supervision and shall withstand all loads likely to be imposed on the structures.

Informational Note: See ANSI C2-2007, National Electrical Safety Code, for additional information on the loading that can be expected to bear on underground enclosures.

110.72 Cabling Work Space. A clear work space not less than 900 mm (3 ft) wide shall be provided where cables are located on both sides, and not less than 750 mm (2½ ft) where cables are only on one side. The vertical headroom shall be not less than 1.8 m (6 ft) unless the opening is within 300 mm (1 ft), measured horizontally, of the adjacent interior side wall of the enclosure.

Exception: A manhole containing only one or more of the following shall be permitted to have one of the horizontal work space dimensions reduced to 600 mm (2 ft) where the other horizontal clear work space is increased so the sum of the two dimensions is not less than 1.8 m (6 ft):

  1. Optical fiber cables as covered in Article 770 70-44
  2. Power-limited fire alarm circuits supplied in accordance with 760.121
  3. Class 2 or Class 3 remote-control and signaling circuits, or both, supplied in accordance with 725.121

110.73 Equipment Work Space. Where electrical equipment with live parts that is likely to require examination, adjustment, servicing, or maintenance while energized is installed in a manhole, vault, or other enclosure designed for personnel access, the work space and associated requirements in 110.26 shall be met for installations operating at 600 volts or less. Where the installation is over 600 volts, the work space and associated requirements in 110.34 shall be met. A manhole access cover that weighs over 45 kg (100 lb) shall be considered as meeting the requirements of 110.34(C).

110.74 Conductor Installation. Conductors installed in manholes and other enclosures intended for personnel entry shall be cabled, racked up, or arranged in an approved manner that provides ready and safe access for persons to enter for installation and maintenance. The installation shall comply with 110.74(A) or 110.74(B), as applicable.

(A) 600 Volts, Nominal, or Less. Wire bending space for conductors operating at 600 volts or less shall be provided in accordance with the requirements of 314.28.

(B) Over 600 Volts, Nominal. Conductors operating at over 600 volts shall be provided with bending space in accordance with 314.71(A) and (B), as applicable.

Exception: Where 314.71(B) applies, each row or column of ducts on one wall of the enclosure shall be calculated individually, and the single row or column that provides the maximum distance shall be used.

110.75 Access to Manholes.

(A) Dimensions. Rectangular access openings shall not be less than 650 mm × 550 mm (26 in. × 22 in.). Round access openings in a manhole shall be not less than 650 mm (26 in.) in diameter.

Exception: A manhole that has a fixed ladder that does not obstruct the opening or that contains only one or more of the following shall be permitted to reduce the minimum cover diameter to 600 mm (2 ft):

  1. Optical fiber cables as covered in Article 770
  2. Power-limited fire alarm circuits supplied in accordance with 760.121
  3. Class 2 or Class 3 remote-control and signaling circuits, or both, supplied in accordance with 725.121

(B) Obstructions. Manhole openings shall be free of protrusions that could injure personnel or prevent ready egress.

(C) Location. Manhole openings for personnel shall be located where they are not directly above electrical equipment or conductors in the enclosure. Where this is not practicable, either a protective barrier or a fixed ladder shall be provided.

(D) Covers. Covers shall be over 45 kg (100 lb) or otherwise designed to require the use of tools to open. They shall be designed or restrained so they cannot fall into the manhole or protrude sufficiently to contact electrical conductors or equipment within the manhole.

(E) Marking. Manhole covers shall have an identifying mark or logo that prominently indicates their function, such as “electric.”

110.76 Access to Vaults and Tunnels.

(A) Location. Access openings for personnel shall be located where they are not directly above electrical equipment or conductors in the enclosure. Other openings shall be permitted over equipment to facilitate installation, maintenance, or replacement of equipment.

(B) Locks. In addition to compliance with the requirements of 110.34, if applicable, access openings for personnel shall be arranged such that a person on the inside can exit when the access door is locked from the outside, or in the case of normally locking by padlock, the locking arrangement shall be such that the padlock can be closed on the locking system to prevent locking from the outside.

110.77 Ventilation. Where manholes, tunnels, and vaults have communicating openings into enclosed areas used by the public, ventilation to open air shall be provided wherever practicable.

110.78 Guarding. Where conductors or equipment, or both, could be contacted by objects falling or being pushed through a ventilating grating, both conductors and live parts shall be protected in accordance with the requirements of 110.27(A)(2) or 110.31(B)(1), depending on the voltage.

110.79 Fixed Ladders. Fixed ladders shall be corrosion resistant.

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Chapter 2 Wiring and Protection

ARTICLE 200
Use and Identification of Grounded Conductors

200.1 Scope. This article provides requirements for the following:

  1. Identification of terminals
  2. Grounded conductors in premises wiring systems
  3. Identification of grounded conductors

Informational Note: See Article 100 for definitions of Grounded Conductor, Equipment Grounding Conductor, and Grounding Electrode Conductor.

200.2 General. Grounded conductors shall comply with 200.2(A) and (B).

(A) Insulation. The grounded conductor, where insulated, shall have insulation that is (1) suitable, other than color, for any ungrounded conductor of the same circuit on circuits of less than 1000 volts or impedance grounded neutral systems of 1 kV and over, or (2) rated not less than 600 volts for solidly grounded neutral systems of 1 kV and over as described in 250.184(A).

(B) Continuity. The continuity of a grounded conductor shall not depend on a connection to a metallic enclosure, raceway, or cable armor.

Informational Note: See 300.13(B) for the continuity of grounded conductors used in multiwire branch circuits.

200.3 Connection to Grounded System. Premises wiring shall not be electrically connected to a supply system unless the latter contains, for any grounded conductor of the interior system, a corresponding conductor that is grounded. For the purpose of this section, electrically connected shall mean connected so as to be capable of carrying current, as distinguished from connection through electromagnetic induction.

Exception: Listed utility-interactive inverters identified for use in distributed resource generation systems such as photovoltaic and fuel cell power systems shall be permitted to be connected to premises wiring without a grounded conductor where the connected premises wiring or utility system includes a grounded conductor.

200.4 Neutral Conductors. Neutral conductors shall not be used for more than one branch circuit, for more than one multiwire branch circuit, or for more than one set of ungrounded feeder conductors unless specifically permitted elsewhere in this Code.

200.6 Means of Identifying Grounded Conductors.

(A) Sizes 6 AWG or Smaller. An insulated grounded conductor of 6 AWG or smaller shall be identified by one of the following means:

  1. A continuous white outer finish.
  2. A continuous gray outer finish.
  3. Three continuous white stripes along the conductor’s entire length on other than green insulation.
  4. Wires that have their outer covering finished to show a white or gray color but have colored tracer threads in the braid identifying the source of manufacture shall be considered as meeting the provisions of this section.
  5. The grounded conductor of a mineral-insulated, metal-sheathed cable shall be identified at the time of installation by distinctive marking at its terminations.
  6. A single-conductor, sunlight-resistant, outdoor-rated cable used as a grounded conductor in photovoltaic power systems, as permitted by 690.31, shall be identified at the time of installation by distinctive white marking at all terminations.
  7. Fixture wire shall comply with the requirements for grounded conductor identification as specified in 402.8.
  8. For aerial cable, the identification shall be as above, or by means of a ridge located on the exterior of the cable so as to identify it.

(B) Sizes 4 AWG or Larger. An insulated grounded conductor 4 AWG or larger shall be identified by one of the following means:

  1. A continuous white outer finish.
  2. A continuous gray outer finish
  3. Three continuous white stripes along its entire length on other than green insulation.
  4. At the time of installation, by a distinctive white or gray marking at its terminations. This marking shall encircle the conductor or insulation.

(C) Flexible Cords. An insulated conductor that is intended for use as a grounded conductor, where contained within a flexible cord, shall be identified by a white or gray outer finish or by methods pemtitted by 400.22.

(D) Grounded Conductors of Different Systems. Where grounded conductors of different systems are installed in the same raceway, cable, box, auxiliary gutter, or other type of enclosure, each grounded conductor shall be identified

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by system. Identification that distinguishes each system grounded conductor shall be permitted by one of the following means:

  1. One system grounded conductor shall have an outer covering conforming to 200.6(A) or (B).
  2. The grounded conductor(s) of other systems shall have a different outer covering conforming to 200.6(A) or 200.6(B) or by an outer covering of white or gray with a readily distinguishable colored stripe other than green running along the insulation.
  3. Other and different means of identification as allowed by 200.6(A) or (B) that will distinguish each system grounded conductor.

The means of identification shall be documented in a manner that is readily available or shall be permanently posted where the conductors of different systems originate.

(E) Grounded Conductors of Multiconductor Cables. The insulated grounded conductors in a multiconductor cable shall be identified by a continuous white or gray outer finish or by three continuous white stripes on other than green insulation along its entire length. Multiconductor flat cable 4 AWG or larger shall be permitted to employ an external ridge on the grounded conductor.

Exception No. 1: Where the conditions of maintenance and supervision ensure that only qualified persons service the installation, grounded conductors in multiconductor cables shall be permitted to be permanently identified at their terminations at the time of installation by a distinctive white marking or other equally effective means.

Exception No. 2: The grounded conductor of a multiconductor varnished-cloth-insulated cable shall be permitted to be identified at its terminations at the time of installation by a distinctive white marking or other equally effective means.

Informational Note: The color gray may have been used in the past as an ungrounded conductor. Care should be taken when working on existing systems.

200.7 Use of Insulation of a White or Gray Color or with Three Continuous White Stripes.

(A) General. The following shall be used only for the grounded circuit conductor, unless otherwise permitted in 200.7(B) and (C):

  1. A conductor with continuous white or gray covering
  2. A conductor with three continuous white stripes on other than green insulation
  3. A marking of white or gray color at the termination

(B) Circuits of Less Than 50 Volts. A conductor with white or gray color insulation or three continuous white stripes or having a marking of white or gray at the termination for circuits of less than 50 volts shall be required to be grounded only as required by 250.20(A).

(C) Circuits of 50 Volts or More. The use of insulation that is white or gray or that has three continuous white stripes for other than a grounded conductor for circuits of 50 volts or more shall be permitted only as in (1) and (2).

  1. If part of a cable assembly that has the insulation permanently reidentified to indicate its use as an ungrounded conductor by marking tape, painting, or other effective means at its termination and at each location where the conductor is visible and accessible. Identification shall encircle the insulation and shall be a color other than white, gray, or green. If used for single-pole, 3-way or 4-way switch loops, the reidentified conductor with white or gray insulation or three continuous white stripes shall be used only for the supply to the switch, but not as a return conductor from the switch to the outlet.
  2. A flexible cord, having one conductor identified by a white or gray outer finish or three continuous white stripes or by any other means permitted by 400.22, that is used for connecting an appliance or equipment permitted by 400.7. This shall apply to flexible cords connected to outlets whether or not the outlet is supplied by a circuit that has a grounded conductor.

Informational Note: The color gray may have been used in the past as an ungrounded conductor. Care should be taken when working on existing systems.

200.9 Means of Identification of Terminals. The identification of terminals to which a grounded conductor is to be connected shall be substantially white in color. The identification of other terminals shall be of a readily distinguishable different color.

Exception: Where the conditions of maintenance and supervision ensure that only qualified persons service the installations, terminals for grounded conductors shall be permitted to be permanently identified at the time of installation by a distinctive white marking or other equally effective means.

200.10 Identification of Terminals.

(A) Device Terminals. All devices, excluding panelboards, provided with terminals for the attachment of conductors and intended for connection to more than one side of the circuit shall have terminals properly marked for identification, unless the electrical connection of the terminal intended to be connected to the grounded conductor is clearly evident.

Exception: Terminal identification shall not be required for devices that have a normal current rating of over 30 amperes, other than polarized attachment plugs and polarized receptacles for attachment plugs as required in 200.10(B).

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(B) Receptacles, Plugs, and Connectors. Receptacles, polarized attachment plugs, and cord connectors for plugs and polarized plugs shall have the terminal intended for connection to the grounded conductor identified as follows:

  1. Identification shall be by a metal or metal coating that is substantially white in color or by the word white or the letter W located adjacent to the identified terminal.
  2. If the terminal is not visible, the conductor entrance hole for the connection shall be colored white or marked with the word white or the letter W.

Informational Note: See 250.126 for identification of wiring device equipment grounding conductor terminals.

(C) Screw Shells. For devices with screw shells, the terminal for the grounded conductor shall be the one connected to the screw shell.

(D) Screw Shell Devices with Leads. For screw shell devices with attached leads, the conductor attached to the screw shell shall have a white or gray finish. The outer finish of the other conductor shall be of a solid color that will not be confused with the white or gray finish used to identify the grounded conductor.

Informational Note: The color gray may have been used in the past as an ungrounded conductor. Care should be taken when working on existing systems.

(E) Appliances. Appliances that have a single-pole switch or a single-pole overcurrent device in the line or any line-connected screw shell lampholders, and that are to be connected by (1) a permanent wiring method or (2) field-installed attachment plugs and cords with three or more wires (including the equipment grounding conductor), shall have means to identify the terminal for the grounded circuit conductor (if any).

200.11 Polarity of Connections. No grounded conductor shall be attached to any terminal or lead so as to reverse the designated polarity.

ARTICLE 210
Branch Circuits

I. General Provisions

210.1 Scope. This article covers branch circuits except for branch circuits that supply only motor loads, which are covered in Article 430. Provisions of this article and Article 430 apply to branch circuits with combination loads.

210.2 Other Articles for Specific-Purpose Branch Circuits. Branch circuits shall comply with this article and also with the applicable provisions of other articles of this Code. The provisions for branch circuits supplying equipment listed in Table 210.2 amend or supplement the provisions in this article and shall apply to branch circuits referred to therein.

210.3 Rating. Branch circuits recognized by this article shall be rated in accordance with the maximum permitted ampere rating or setting of the overcurrent device. The rating for other than individual branch circuits shall be 15, 20, 30, 40, and 50 amperes. Where conductors of higher ampacity are used for any reason, the ampere rating or setting of the specified overcurrent device shall determine the circuit rating.

Exception: Multioutlet branch circuits greater than 50 amperes shall be permitted to supply nonlighting outlet loads on industrial premises where conditions of maintenance and supervision ensure that only qualified persons service the equipment.

210.4 Multiwire Branch Circuits.

(A) General. Branch circuits recognized by this article shall be permitted as multiwire circuits. A multiwire circuit shall be permitted to be considered as multiple circuits. All conductors of a multiwire branch circuit shall originate from the same panelboard or similar distribution equipment.

Informational Note: A 3-phase, 4-wire, wye-connected power-system used to supply power to nonlinear loads may necessitate that the power system design allow for the possibility of high harmonic currents on the neutral conductor.

(B) Disconnecting Means. Each multiwire branch circuit shall be provided with a means that will simultaneously disconnect all ungrounded conductors at the point where the branch circuit originates.

Informational Note: See 240.15(B) for information on the use of single-pole circuit breakers as the disconnecting means.

(C) Line-to-Neutral Loads. Multiwire branch circuits shall supply only line-to-neutral loads.

Exception No. 1: A multiwire branch circuit that supplies only one utilization equipment.

Exception No. 2: Where all ungrounded conductors of the multiwire branch circuit are opened simultaneously by the branch-circuit overcurrent device.

Informational Note: See 300.13(B) for continuity of grounded conductor on multiwire circuits.

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Table 210.2 Specific-Purpose Branch Circuits
Equipment Article Section
Air-conditioning and refrigerating equipment   440.6, 440.31, 440.32
Audio signal processing, amplification, and reproduction equipment   640.8
Busways   368.17
Circuits and equipment operating at less than 50 volts 720  
Central heating equipment other than fixed electric space-heating equipment   422.12
Class 1, Class 2, and Class 3 remote-control, signaling, and power-limited circuits 725  
Cranes and hoists   610.42
Electric signs and outline lighting   600.6
Electric welders 630  
Electrified truck parking space 626  
Elevators, dumbwaiters, escalators, moving walks, wheelchair lifts, and stairway chair lifts.   620.61
Fire alarm systems 760  
Fixed electric heating equipment for pipelines and vessels   427.4
Fixed electric space-heating equipment   424.3
Fixed outdoor electrical deicing and snow-melting equipment   426.4
Information technology equipment   645.5
Infrared lamp industrial heating equipment   422.48, 424.3
Induction and dielectric heating equipment 665  
Marinas and boatyards   555.19
Mobile homes, manufactured homes, and mobile home parks 550  
Motion picture and television studios and similar locations 530  
Motors, motor circuits, and controllers 430  
Pipe organs   650.7
Recreational vehicles and recreational vehicle parks 551  
Switchboards and panelboards   408.52
Theaters, audience areas of motion picture and television studios, and similar locations   520.41, 520.52, 520.62
X-ray equipment   660.2, 517.73

(D) Grouping. The ungrounded and grounded circuit conductors of each multiwire branch circuit shall be grouped by cable ties or similar means in at least one location within the panelboard or other point of origination.

Exception: The requirement for grouping shall not apply if the circuit enters from a cable or raceway unique to the circuit that makes the grouping obvious.

210.5 Identification for Branch Circuits.

(A) Grounded Conductor. The grounded conductor of a branch circuit shall be identified in accordance with 200.6.

(B) Equipment Grounding Conductor. The equipment grounding conductor shall be identified in accordance with 250.119.

(C) Identification of Ungrounded Conductors. Ungrounded conductors shall be identified in accordance with 210.5(C)(1), (2). and (3).

(1) Application. Where the premises wiring system has branch circuits supplied from more than one nominal voltage system, each ungrounded conductor of a branch circuit shall be identified by phase or line and system at all termination, connection, and splice points.

(2) Means of Identification. The means of identification shall be permitted to be by separate color coding, marking tape, tagging, or other approved means.

(3) Posting of Identification Means. The method utilized for conductors originating within each branch-circuit panelboard or similar branch-circuit distribution equipment shall be documented in a manner that is readily available or shall be permanently posted at each branch-circuit panel-board or similar branch-circuit distribution equipment.

210.6 Branch-Circuit Voltage Limitations. The nominal voltage of branch circuits shall not exceed the values permitted by 210.6(A) through (E).

(A) Occupancy Limitation. In dwelling units and guest rooms or guest suites of hotels, motels, and similar occupancies, the voltage shall not exceed 120 volts, nominal, between conductors that supply the terminals of the following:

  1. Luminaires
  2. Cord-and-plug-connected loads 1440 volt-amperes, nominal, or less or less than ¼ hp

(B) 120 Volts Between Conductors. Circuits not exceeding 120 volts, nominal, between conductors shall be permitted to supply the following:

  1. The terminals of lampholders applied within their voltage ratings
  2. Auxiliary equipment of electric-discharge lamps
  3. Cord-and-plug-connected or permanently connected utilization equipment
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(C) 277 Volts to Ground. Circuits exceeding 120 volts, nominal, between conductors and not exceeding 277 volts, nominal, to ground shall be permitted to supply the following:

  1. Listed electric-discharge or listed light-emitting diode-type luminaires
  2. Listed incandescent luminaires, where supplied at 120 volts or less from the output of a stepdown autotransformer that is an integral component of the luminaire and the outer shell terminal is electrically connected to a grounded conductor of the branch circuit
  3. Luminaires equipped with mogul-base screw shell lampholders
  4. Lampholders, other than the screw shell type, applied within their voltage ratings
  5. Auxiliary equipment of electric-discharge lamps
  6. Cord-and-plug-connected or permanently connected utilization equipment

(D) 600 Volts Between Conductors. Circuits exceeding 277 volts, nominal, to ground and not exceeding 600 volts, nominal, between conductors shall be permitted to supply the following:

  1. The auxiliary equipment of electric-discharge lamps mounted in permanently installed luminaires where the luminaires are mounted in accordance with one of the following:
    1. Not less than a height of 6.7 m (22 ft) on poles or similar structures for the illumination of outdoor areas such as highways, roads, bridges, athletic fields, or parking lots
    2. Not less than a height of 5.5 m (18 ft) on other structures such as tunnels
  2. Cord-and-plug-connected or permanently connected utilization equipment other than luminaires
  3. Luminaires powered from direct-current systems where the luminaire contains a listed, dc-rated ballast that provides isolation between the dc power source and the lamp circuit and protection from electric shock when changing lamps.

Informational Note: See 410.138 for auxiliary equipment limitations.

Exception No. 1 to (B), (C), and (D): For lampholders of infrared industrial heating appliances as provided in 422.14.

Exception No. 2 to (B), (C), and (D): For railway properties as described in 110.19.

(E) Over 600 Volts Between Conductors. Circuits exceeding 600 volts, nominal, between conductors shall be permitted to supply utilization equipment in installations where conditions of maintenance and supervision ensure that only qualified persons service the installation.

210.7 Multiple Branch Circuits. Where two or more branch circuits supply devices or equipment on the same yoke, a means to simultaneously disconnect the ungrounded conductors supplying those devices shall be provided at the point at which the branch circuits originate.

210.8 Ground-Fault Circuit-Interrupter Protection for Personnel. Ground-fault circuit-interruption for personnel shall be provided as required in 210.8(A) through (C). The ground-fault circuit-interrupter shall be installed in a readily accessible location.

Informational Note: See 215.9 for ground-fault circuit-interrupter protection for personnel on feeders.

(A) Dwelling Units. All 125-volt, single-phase, 15- and 20-ampere receptacles installed in the locations specified in 210.8(A)(1) through (8) shall have ground-fault circuit-interrupter protection for personnel.

  1. Bathrooms
  2. Garages, and also accessory buildings that have a floor located at or below grade level not intended as habitable rooms and limited to storage areas, work areas, and areas of similar use
  3. Outdoors Exception to (3): Receptacles that are not readily accessible and are supplied by a branch circuit dedicated to electric snow-melting, deicing. or pipeline and vessel heating equipment shall be permitted to be installed in accordance with 426.28 or 427.22, as applicable.
  4. Crawl spaces — at or below grade level
  5. Unfinished basements — for purposes of this section, unfinished basements are defined as portions or areas of the basement not intended as habitable rooms and limited to storage areas, work areas, and the like

    Exception to (5): A receptacle supplying only a permanently installed fire alarm or burglar alarm system shall not be required to have ground-fault circuit-interrupter protection.

    Informational Note: See 760.41(B) and 760.121(B) for power supply requirements for fire alarm systems.

    Receptacles installed under the exception to 210.8(A)(5) shall not be considered as meeting the requirements of 210.52(G).

  6. Kitchens— where the receptacles are installed to serve the countertop surfaces
  7. Sinks — located in areas other than kitchens where receptacles are installed within 1.8 m (6 ft) of the outside edge of the sink
  8. Boathouses
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(B) Other Than Dwelling Units. All 125 volt, single-phase, 15- and 20-ampere receptacles installed in the locations specified in 210.8(B)(1) through (8) shall have ground-fault circuit-interrupter protection for personnel.

  1. Bathrooms
  2. Kitchens
  3. Rooftops
  4. Outdoors

    Exception No. 1 to (3) and (4): Receptacles that are not readily accessible and are supplied by a branch circuit dedicated to electric snow-melting, deicing, or pipeline and vessel heating equipment shall be permitted to be installed in accordance with 426.28 or 427.22, as applicable.

    Exception No. 2 to (4): In industrial establishments only, where the conditions of maintenance and supervision ensure that only qualified personnel are involved, an assured equipment grounding conductor program as specified in 590.6(B)(2) shall be permitted for only those receptacle outlets used to supply equipment that would create a greater hazard if power is interrupted or having a design that is not compatible with GFCI protection.

  5. Sinks — where receptacles are installed within 1.8 m (6 ft) of the outside edge of the sink.

    Exception No. 1 to (5): In industrial laboratories, receptacles used to supply equipment where removed of power would introduce a greater hazard shall be permitted to be installed without GFCI protection.

    Exception No. 2 to (5): For receptacles located in patient bed locations of general care or critical care areas of health care facilities other than those covered under 210.8(B)(1), GFCI protection shall not be required.

  6. Indoor wet locations
  7. Locker rooms with associated showering facilities
  8. Garages, service bays, and similar areas where electrical diagnostic equipment, electrical hand tools, or portable lighting equipment are to be used

(C) Boat Hoists. GFCI protection shall be provided for outlets not exceeding 240 volts that supply boat hoists installed in dwelling unit locations.

210.9 Circuits Derived from Autotransformers. Branch circuits shall not be derived from autotransformers unless the circuit supplied has a grounded conductor that is electrically connected to a grounded conductor of the system supplying the autotransformer.

Exception No. 1: An autotransformer shall be permitted without the connection to a grounded conductor where transforming from a nominal 208 volts to a nominal 240-volt supply or similarly from 240 volts to 208 volts.

Exception No. 2: In industrial occupancies, where conditions of maintenance and supervision ensure that only qualified persons service the installation, autotransformers shall be permitted to supply nominal 600-volt loads from nominal 480-volt systems, and 480-volt loads from nominal 600-volt systems, without the connection to a similar grounded conductor.

210.10 Ungrounded Conductors Tapped from Grounded Systems. Two-wire dc circuits and ac circuits of two or more ungrounded conductors shall be permitted to be tapped from the ungrounded conductors of circuits that have a grounded neutral conductor. Switching devices in each tapped circuit shall have a pole in each ungrounded conductor. All poles of multipole switching devices shall manually switch together where such switching devices also serve as a disconnecting means as required by the following:

  1. 410.93 for double-pole switched lampholders
  2. 410.104(B) for electric-discharge lamp auxiliary equipment switching devices
  3. 422.31(B) for an appliance
  4. 424.20 for a fixed electric space-heating unit
  5. 426.51 for electric deicing and snow-melting equipment
  6. 430.85 for a motor controller
  7. 430.103 for a motor

210.11 Branch Circuits Required. Branch circuits for lighting and for appliances, including motor-operated appliances, shall be provided to supply the loads calculated in accordance with 220.10. In addition, branch circuits shall be provided for specific loads not covered by 220.10 where required elsewhere in this Code and for dwelling unit loads as specified in 210.11(C).

(A) Number of Branch Circuits. The minimum number of branch circuits shall be determined from the total calculated load and the size or rating of the circuits used. In all installations, the number of circuits shall be sufficient to supply the load served. In no case shall the load on any circuit exceed the maximum specified by 220.18.

(B) Load Evenly Proportioned Among Branch Circuits. Where the load is calculated on the basis of volt-amperes per square meter or per square foot, the wiring system up to and including the branch-circuit panelboard(s) shall be provided to serve not less than the calculated load. This load shall be evenly proportioned among multioutlet branch circuits within the panelboard(s). Branch-circuit overcurrent devices and circuits shall be required to be installed only to serve the connected load.

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(C) Dwelling Units.

(1) Small-Appliance Branch Circuits. In addition to the number of branch circuits required by other parts of this section, two or more 20-ampere small-appliance branch circuits shall be provided for all receptacle outlets specified by 210.52(B).

(2) Laundry Branch Circuits. In addition to the number of branch circuits required by other parts of this section, at least one additional 20-ampere branch circuit shall be provided to supply the laundry receptacle outlet(s) required by 210.52(F). This circuit shall have no other outlets.

(3) Bathroom Branch Circuits. In addition to the number of branch circuits required by other parts of this section, at least one 20-ampere branch circuit shall be provided to supply bathroom receptacle outlet(s). Such circuits shall have no other outlets.

Exception: Where the 20-ampere circuit supplies a single bathroom, outlets for other equipment within the same bathroom shall be permitted to be supplied in accordance with 210.23(A)(1) and (A)(2).

Informational Note: See Examples Dl(a), Dl(b), D2(b), and D4(a) in Informative Annex D.

210.12 Arc-Fault Circuit-Interrupter Protection.

(A) Dwelling Units. All 120-volt, single phase, 15- and 20-ampere branch circuits supplying outlets installed in dwelling unit family rooms, dining rooms, living rooms, parlors, libraries, dens, bedrooms, sunrooms, recreation rooms, closets, hallways, or similar rooms or areas shall be protected by a listed arc-fault circuit interrupter, combination-type, installed to provide protection of the branch circuit.

Informational Note No. 1: For information on types of arc-fault circuit interrupters, see UL 1699-1999, Standard for Arc-Fault Circuit Interrupters.

Informational Note No. 2: See 11.6.3(5) of NFPA 72-2010, National Fire Alarm and Signaling Code, for information related to secondary power supply requirements for smoke alarms installed in dwelling units.

Informational Note No. 3: See 760.41(B) and 760.121(B) for power-supply requirements for fire alarm systems.

Exception No. 1: If RMC, IMC, EMT, Type MC, or steel armored Type AC cables meeting the requirements of 250.118 and metal outlet and junction boxes are installed for the portion of the branch circuit between the branch-circuit overcurrent device and the first outlet, it shall be permitted to install an outlet branch-circuit type AFCI at the first outlet to provide protection for the remaining portion of the branch circuit.

Exception No. 2: Where a listed metal or nonmetallic conduit or tubing is encased in not less than 50 mm (2 in.) of concrete for the portion of the branch circuit between the branch-circuit overcurrent device and the first outlet, it shall be permitted to install an outlet branch-circuit type AFCI at the first outlet to provide protection for the remaining portion of the branch circuit.

Exception No. 3: Where an individual branch circuit to a fire alarm system installed in accordance with 760.41(B) or 760.121(B) is installed in RMC, IMC, EMT, or steel-sheathed cable, Type AC or Type MC, meeting the requirements of 250.118, with meted outlet and junction boxes, AFCI protection shall be permitted to be omitted.

(B) Branch Circuit Extensions or Modifications — Dwelling Units. In any of the areas specified in 210.12(A), where branch-circuit wiring is modified, replaced, or extended, the branch circuit shall be protected by one of the following:

  1. A listed combination-type AFCI located at the origin of the branch circuit
  2. A listed outlet branch-circuit type AFCI located at the first receptacle outlet of the existing branch circuit

210.18 Guest Rooms and Guest Suites. Guest rooms and guest suites that are provided with permanent provisions for cooking shall have branch circuits installed to meet the rules for dwelling units.

II. Branch-Circuit Ratings

210.19 Conductors — Minimum Ampacity and Size.

(A) Branch Circuits Not More Than 600 Volts.

(1) General. Branch-circuit conductors shall have an ampacity not less than the maximum load to be served. Where a branch circuit supplies continuous loads or any combination of continuous and noncontinuous loads, the minimum branch-circuit conductor size, before the application of any adjustment or correction factors, shall have an allowable ampacity not less than the noncontinuous load plus 125 percent of the continuous load.

Exception: If the assembly, including the overcurrent devices protecting the branch circuits), is listed for operation at 100 percent of its rating, the allowable ampacity of the branch circuit conductors shall be permitted to be not less than the sum of the continuous load plus the noncontinuous load.

Informational Note No. 1: See 310.15 for ampacity ratings of conductors.

Informational Note No. 2: See Part II of Article 430 for minimum rating of motor branch-circuit conductors.

Informational Note No. 3: See 310.15(A)(3) for temperature limitation of conductors.

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Informational Note No. 4: Conductors for branch circuits as defined in Article 100, sized to prevent a voltage drop exceeding 3 percent at the farthest outlet of power, heating, and lighting loads, or combinations of such loads, and where the maximum total voltage drop on both feeders and branch circuits to the farthest outlet does not exceed 5 percent, provide reasonable efficiency of operation. See Informational Note No. 2 of 215.2(A)(3) for voltage drop on feeder conductors.

(2) Branch Circuits with More than One Receptacle. Conductors of branch circuits supplying more than one receptacle for cord-and-plug-connected portable loads shall have an ampacity of not less than the rating of the branch circuit.

(3) Household Ranges and Cooking Appliances. Branch-circuit conductors supplying household ranges, wall-mounted ovens, counter-mounted cooking units, and other household cooking appliances shall have an ampacity not less than the rating of the branch circuit and not less than the maximum load to be served. For ranges of 8¾ kW or more rating, the minimum branch-circuit rating shall be 40 amperes.

Exception No. 1: Conductors tapped from a 50-ampere branch circuit supplying electric ranges, wall-mounted electric ovens, and counter-mounted electric cooking units shall have an ampacity of not less than 20 amperes and shall be sufficient for the load to be served. These tap conductors include any conductors that are a part of the leads supplied with the appliance that are smaller than the branch-circuit conductors. The taps shall not be longer than necessary for servicing the appliance.

Exception No. 2: The neutral conductor of a 3-wire branch circuit supplying a household electric range, a wall-mounted oven, or a counter-mounted cooking unit shall be permitted to be smaller than the ungrounded conductors where the maximum demand of a range of 8¾-kW or more rating has been calculated according to Column C of Table 220.55, but such conductor shall have an ampacity of not less than 70 percent of the branch-circuit rating and shall not be smaller than 10 AWG.

(4) Other Loads. Branch-circuit conductors that supply loads other than those specified in 210.2 and other than cooking appliances as covered in 210.19(A)(3) shall have an ampacity sufficient for the loads served and shall not be smaller than 14 AWG.

Exception No. 1: Tap conductors shall have an ampacity sufficient for the load served. In addition, they shall have an ampacity of not less than 15 for circuits rated less than 40 amperes and not less than 20 for circuits rated at 40 or 50 amperes and only where these tap conductors supply any of the following loads:

(a) Individual lampholders or luminaires with taps extending not longer than 450 mm (18 in.) beyond any portion of the lampholder or luminaire.

(b) A luminaire having tap conductors as provided in 410.117.

(c) Individual outlets, other than receptacle outlets, with taps not over 450 mm (18 in.) long.

(d) Infrared lamp industrial heating appliances.

(e) Nonheating leads of deicing and snow-melting cables and mats.

Exception No. 2: Fixture wires and flexible cords shall be permitted to be smaller than 14 AWG as permitted by 240.5.

(B) Branch Circuits Over 600 Volts. The ampacity of conductors shall be in accordance with 310.15 and 310.60, as applicable. Branch-circuit conductors over 600 volts shall be sized in accordance with 210.19(B)(1) or (B)(2).

(1) General. The ampacity of branch-circuit conductors shall not be less than 125 percent of the designed potential load of utilization equipment that will be operated simultaneously.

(2) Supervised Installations. For supervised installations, branch-circuit conductor sizing shall be permitted to be determined by qualified persons under engineering supervision. Supervised installations are defined as those portions of a facility where both of the following conditions are met:

  1. Conditions of design and installation are provided under engineering supervision.
  2. Qualified persons with documented training and experience in over 600-volt systems provide maintenance, monitoring, and servicing of the system.

210.20 Overcurrent Protection. Branch-circuit conductors and equipment shall be protected by overcurrent protective devices that have a rating or setting that complies with 210.20(A) through (D).

(A) Continuous and Noncontinuous Loads. Where a branch circuit supplies continuous loads or any combination of continuous and noncontinuous loads, the rating of the overcurrent device shall not be less than the non-continuous load plus 125 percent of the continuous load.

Exception: Where the assembly, including the overcurrent devices protecting the branch circuit(s), is listed for operation at 100 percent of its rating, the ampere rating of the overcurrent device shall be permitted to be not less than the sum of the continuous load plus the noncontinuous load.

(B) Conductor Protection. Conductors shall be protected in accordance with 240.4. Flexible cords and fixture wires shall be protected in accordance with 240.5.

(C) Equipment. The rating or setting of the overcurrent protective device shall not exceed that specified in the applicable articles referenced in Table 240.3 for equipment.

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(D) Outlet Devices. The rating or setting shall not exceed that specified in 210.21 for outlet devices.

210.21 Outlet Devices. Outlet devices shall have an ampere rating that is not less than the load to be served and shall comply with 210.21(A) and (B).

(A) Lampholders. Where connected to a branch circuit having a rating in excess of 20 amperes, lampholders shall be of the heavy-duty type. A heavy-duty lampholder shall have a rating of not less than 660 watts if of the admedium type, or not less than 750 watts if of any other type.

(B) Receptacles.

(1) Single Receptacle on an Individual Branch Circuit. A single receptacle installed on an individual branch circuit shall have an ampere rating not less than that of the branch circuit.

Exception No. 1: A receptacle installed in accordance with 430.81(B).

Exception No. 2: A receptacle installed exclusively for the use of a cord-and-plug-connected arc welder shall be permitted to have an ampere rating not less than the minimum branch-circuit conductor ampacity determined by 630.11(A) for arc welders.

Informational Note: See the definition of receptacle in Article 100.

(2) Total Cord-and-Plug-Connected Load. Where connected to a branch circuit supplying two or more receptacles or outlets, a receptacle shall not supply a total cord-and-plug-connected load in excess of the maximum specified in Table 210.21(B)(2).

Table 210.21(B)(2) Maximum Cord-and-Plug -Connected Load to Receptacle
Circuit Rating
(Amperes)
Receptacle Rating
(Amperes)
Maximum Load
(Amperes)
15 or 20 15 12
20 20 16
30 30 24

(3) Receptacle Ratings. Where connected to a branch circuit supplying two or more receptacles or outlets, receptacle ratings shall conform to the values listed in Table 210.21(B)(3), or, where rated higher than 50 amperes, the receptacle rating shall not be less than the branch-circuit rating.

Exception No. 1: Receptacles for one or more cord-and-plug-connected arc welders shall be permitted to have ampere ratings not less than the minimum branch-circuit conductor ampacity permitted by 630.11(A) or (B), as applicable for arc welders.

Exception No. 2: The ampere rating of a receptacle installed for electric discharge lighting shall be permitted to be based on 410.62(C).

Table 210.21(B)(3) Receptacle Ratings for Various Size Circuits
Circuit Rating
(Amperes)
Receptacle Rating
(Amperes)
15 Not over 15
20 15 or 20
30 30
40 40 or 50
50 50

(4) Range Receptacle Rating. The ampere rating of a range receptacle shall be permitted to be based on a single range demand load as specified in Table 220.55.

210.23 Permissible Loads. In no case shall the load exceed the branch-circuit ampere rating. An individual branch circuit shall be permitted to supply any load for which it is rated. A branch circuit supplying two or more outlets or receptacles shall supply only the loads specified according to its size as specified in 210.23(A) through (D) and as summarized in 210.24 and Table 210.24.

(A) 15- and 20-Ampere Branch Circuits. A 15- or 20-ampere branch circuit shall be permitted to supply lighting units or other utilization equipment, or a combination of both, and shall comply with 210.23(A)(1) and (A)(2).

Exception: The small-appliance branch circuits, laundry branch circuits, and bathroom branch circuits required in a dwelling unit(s) by 210.11(C)(1), (C)(2), and (C)(3) shall supply only the receptacle outlets specified in that section.

(1) Cord-and-Plug-Connected Equipment Not Fastened in Place. The rating of any one cord-and-plug-connected utilization equipment not fastened in place shall not exceed 80 percent of the branch-circuit ampere rating.

(2) Utilization Equipment Fastened in Place. The total rating of utilization equipment fastened in place, other than luminaires, shall not exceed 50 percent of the branch-circuit ampere rating where lighting units, cord-and-plug-connected utilization equipment not fastened in place, or both, are also supplied.

(B) 30-Ampere Branch Circuits. A 30-ampere branch circuit shall be permitted to supply fixed lighting units with heavy-duty lampholders in other than a dwelling unit(s) or utilization equipment in any occupancy. A rating of any one

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cord-and-plug-connected utilization equipment shall not exceed 80 percent of the branch-circuit ampere rating.

(C) 40- and 50-Ampere Branch Circuits. A 40- or 50- ampere branch circuit shall be permitted to supply cooking appliances that are fastened in place in any occupancy. In other than dwelling units, such circuits shall be permitted to supply fixed lighting units with heavy-duty lampholders, infrared heating units, or other utilization equipment.

(D) Branch Circuits Larger Than 50 Amperes. Branch circuits larger than 50 amperes shall supply only nonlighting outlet loads.

210.24 Branch-Circuit Requirements — Summary. The requirements for circuits that have two or more outlets or receptacles, other than the receptacle circuits of 210.11(C)(1), (C)(2), and (C)(3), are summarized in Table 210.24. This table provides only a summary of minimum requirements. See 210.19, 210.20, and 210.21 for the specific requirements applying to branch circuits.

210.25 Branch Circuits in Buildings with More Than One Occupancy.

(A) Dwelling Unit Branch Circuits. Branch circuits in each dwelling unit shall supply only loads within that dwelling unit or loads associated only with that dwelling unit.

(B) Common Area Branch Circuits. Branch circuits installed for the purpose of lighting, central alarm, signal, communications, or other purposes for public or common areas of a two-family dwelling, a multifamily dwelling, or a multi-occupancy building shall not be supplied from equipment that supplies an individual dwelling unit or tenant space.

III. Required Outlets

210.50 General. Receptacle outlets shall be installed as specified in 210.52 through 210.63.

(A) Cord Pendants. A cord connector that is supplied by a permanently connected cord pendant shall be considered a receptacle outlet.

(B) Cord Connections. A receptacle outlet shall be installed wherever flexible cords with attachment plugs are used. Where flexible cords are permitted to be permanently connected, receptacles shall be permitted to be omitted for such cords.

(C) Appliance Receptacle Outlets. Appliance receptacle outlets installed in a dwelling unit for specific appliances, such as laundry equipment, shall be installed within 1.8 m (6 ft) of the intended location of the appliance.

210.52 Dwelling Unit Receptacle Outlets. This section provides requirements for 125-volt, 15- and 20-ampere receptacle outlets. The receptacles required by this section shall be in addition to any receptacle that is:

  1. Part of a luminaire or appliance, or
  2. Controlled by a wall switch in accordance with 210.70(A)(1), Exception No. 1, or
  3. Located within cabinets or cupboards, or
  4. Located more than 1.7 m (5½ ft) above the floor

Permanently installed electric baseboard heaters equipped with factory-installed receptacle outlets or outlets provided as a separate assembly by the manufacturer shall be permitted as the required outlet or outlets for the wall space utilized by

Table 210.24 Summary of Branch-Circuit Requirements
Circuit Rating 15 A 20 A 30 A 40 A 50 A
Conductors (min. size):
    Circuit wires1
14 12 10 8 6
    Taps 14 14 14 12 12
    Fixture wires and cords
— see 240.5
    Overcurrent Protection 15 A 20 A 30 A 40 A 50 A
Outlet devices:
    Lampholders
Any type Any type Heavy duty Heavy duty Heavy duty
    permitted
    Receptacle rating2
15 max. A 15 or 20 A 30 A 40 or 50 A 50 A
    Maximum Load 15 A 20 A 30 A 40 A 50 A
Permissible load See 210.23(A) See 210.23(A) See 210.23(B) See 210.23(C) See 210.23(C)
1 These gauges are for copper conductors.
2 For receptacle rating of cord-connected electric-discharge luminaires, see 410.62(C).
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such permanently installed heaters. Such receptacle outlets shall not be connected to the heater circuits.

Informational Note: Listed baseboard heaters include instructions that may not permit their installation below receptacle outlets.

(A) General Provisions. In every kitchen, family room, dining room, living room, parlor, library, den, sunroom, bedroom, recreation room, or similar room or area of dwelling units, receptacle outlets shall be installed in accordance with the general provisions specified in 210.52(A)(1) through (A)(3).

(1) Spacing. Receptacles shall be installed such that no point measured horizontally along the floor line of any wall space is more than 1.8 m (6 ft) from a receptacle outlet.

(2) Wall Space. As used in this section, a wall space shall include the following:

  1. Any space 600 mm (2 ft) or more in width (including space measured around corners) and unbroken along the floor line by doorways and similar openings, fireplaces, and fixed cabinets
  2. The space occupied by fixed panels in exterior walls, excluding sliding panels
  3. The space afforded by fixed room dividers, such as freestanding bar-type counters or railings

(3) Floor Receptacles. Receptacle outlets in floors shall not be counted as part of the required number of receptacle outlets unless located within 450 mm (18 in.) of the wall.

(4) Countertop Receptacles. Receptacles installed for countertop surfaces as specified in 210.52(C) shall not be considered as the receptacles required by 210.52(A).

(B) Small Appliances.

(1) Receptacle Outlets Served. In the kitchen, pantry, breakfast room, dining room, or similar area of a dwelling unit, the two or more 20-ampere small-appliance branch circuits required by 210.11(C)(1) shall serve all wall and floor receptacle outlets covered by 210.52(A), all counter-top outlets covered by 210.52(C), and receptacle outlets for refrigeration equipment.

Exception No. 1: In addition to the required receptacles specified by 210.52, switched receptacles supplied from a general-purpose branch circuit as defined in 210.70(A)(1), Exception No. 1, shall be permitted.

Exception No. 2: The receptacle outlet for refrigeration equipment shall be permitted to be supplied from an individual branch circuit rated 15 amperes or greater.

(2) No Other Outlets. The two or more small-appliance branch circuits specified in 210.52(B)(1) shall have no other outlets.

Exception No. 1: A receptacle installed solely for the electrical supply to and support of an electric clock in any of the rooms specified in 210.52(B)(1).

Exception No. 2: Receptacles installed to provide power for supplemental equipment and lighting on gas-fired ranges, ovens, or counter-mounted cooking units.

(3) Kitchen Receptacle Requirements. Receptacles installed in a kitchen to serve countertop surfaces shall be supplied by not fewer than two small-appliance branch circuits, either or both of which shall also be permitted to supply receptacle outlets in the same kitchen and in other rooms specified in 210.52(B)(1). Additional small-appliance branch circuits shall be permitted to supply receptacle outlets in the kitchen and other rooms specified in 210.52(B)(1). No small-appliance branch circuit shall serve more than one kitchen.

(C) Countertops. In kitchens, pantries, breakfast rooms, dining rooms, and similar areas of dwelling units, receptacle outlets for countertop spaces shall be installed in accordance with 210.52(C)(1) through (C)(5).

(1) Wall Countertop Spaces. A receptacle outlet shall be installed at each wall countertop space that is 300 mm (12 in.) or wider. Receptacle outlets shall be installed so that no point along the wall line is more than 600 mm (24 in.) measured horizontally from a receptacle outlet in that space.

Exception: Receptacle outlets shall not be required on a wall directly behind a range, counter-mounted cooking unit, or sink in the installation described in Figure 210.52(C)(1).

(2) Island Countertop Spaces. At least one receptacle shall be installed at each island countertop space with a long dimension of 600 mm (24 in.) or greater and a short dimension of 300 mm (12 in.) or greater.

(3) Peninsular Countertop Spaces. At least one receptacle outlet shall be installed at each peninsular countertop space with a long dimension of 600 mm (24 in.) or greater and a short dimension of 300 mm (12 in.) or greater. A peninsular countertop is measured from the connecting edge.

(4) Separate Spaces. Countertop spaces separated by rangetops, refrigerators, or sinks shall be considered as separate countertop spaces in applying the requirements of 210.52(C)(1). If a range, counter-mounted cooking unit, or sink is installed in an island or peninsular countertop and the depth of the countertop behind the range, counter-mounted cooking unit, or sink is less than 300 mm (12 in.), the range, counter-mounted cooking unit, or sink shall be considered to divide the countertop space into two separate countertop spaces. Each separate countertop space shall comply with the applicable requirements in 210.52(C).

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Figure 210.52(C)(1) Determination of Area Behind a Range, or Counted-Mounted Cooking Unit or Sink

Figure 210.52(C)(1) Determination of Area Behind a Range, or Counted-Mounted Cooking Unit or Sink.

(5) Receptacle Outlet Location. Receptacle outlets shall be located on or above, but not more than 500 mm (20 in.) above, the countertop. Receptacle outlet assemblies listed for the application shall be permitted to be installed in countertops. Receptacle outlets rendered not readily accessible by appliances fastened in place, appliance garages, sinks, or rangetops as covered in 210.52(C)(1), Exception, or appliances occupying dedicated space shall not be considered as these required outlets.

Informational Note: See 406.5(E) for requirements for installation of receptacles in countertops.

Exception to (5): To comply with the conditions specified in (1) or (2), receptacle outlets shall be permitted to be mounted not more than 300 mm (12 in.) below the counter-top. Receptacles mounted below a countertop in accordance with this exception shall not be located where the countertop extends more than 150 mm (6 in.) beyond its support base.

(1) Construction for the physically impaired

(2) On island and peninsular countertops where the countertop is flat across its entire surface (no backsplashes, dividers, etc.) and there are no means to mount a receptacle within 500 mm (20 in.) above the countertop, such as an overhead cabinet

(D) Bathrooms. In dwelling units, at least one receptacle outlet shall be installed in bathrooms within 900 mm (3 ft) of the outside edge of each basin. The receptacle outlet shall be located on a wall or partition that is adjacent to the basin or basin countertop, located on the countertop, or installed on the side or face of the basin cabinet not more than 300 mm (12 in.) below the countertop. Receptacle outlet assemblies listed for the application shall be permitted to be installed in the countertop.

Informational Note: See 406.5(E) for requirements for installation of receptacles in countertops.

(E) Outdoor Outlets. Outdoor receptacle outlets shall be installed in accordance with (E)(1) through (E)(3). [See 210.8(A)(3).]

(1) One-Family and Two-Family Dwellings. For a one-family dwelling and each unit of a two-family dwelling that is at grade level, at least one receptacle outlet accessible while standing at grade level and located not more than 2.0 m (6½ ft) above grade shall be installed at the front and back of the dwelling.

(2) Multifamily Dwellings. For each dwelling unit of a multifamily dwelling where the dwelling unit is located at grade level and provided with individual exterior entrance/egress, at least one receptacle outlet accessible from grade level and not more than 2.0 m (6½ ft) above grade shall be installed.

(3) Balconies, Decks, and Porches. Balconies, decks, and porches that are accessible from inside the dwelling unit shall have at least one receptacle outlet installed within the perimeter of the balcony, deck, or porch. The receptacle shall not be located more than 2.0 m (6½ ft) above the balcony, deck, or porch surface.

(F) Laundry Areas. In dwelling units, at least one receptacle outlet shall be installed for the laundry.

Exception No. 1: In a dwelling unit that is an apartment or living area in a multifamily building where laundry facilities are provided on the premises and are available to all building occupants, a laundry receptacle shall not be required.

Exception No. 2: In other than one-family dwellings where laundry facilities are not to be installed or permitted, a laundry receptacle shall not be required.

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(G) Basements, Garages, and Accessory Buildings. For a one-family dwelling, the following provisions shall apply:

  1. At least one receptacle outlet, in addition to those for specific equipment, shall be installed in each basement, in each attached garage, and in each detached garage or accessory building with electric power.
  2. Where a portion of the basement is finished into one or more habitable rooms, each separate unfinished portion shall have a receptacle outlet installed in accordance with this section.

(H) Hallways. In dwelling units, hallways of 3.0 in (10 ft) or more in length shall have at least one receptacle outlet.

As used in this subsection, the hallway length shall be considered the length along the centerline of the hallway without passing through a doorway.

(I) Foyers. Foyers that are not part of a hallway in accordance with 210.52(H) and that have an area that is greater than 5.6 m2 (60 ft2) shall have a receptacle(s) located in each wall space 900 mm (3 ft) or more in width and unbroken by doorways, floor-to-ceiling windows, and similar openings.

210.60 Guest Rooms, Guest Suites, Dormitories, and Similar Occupancies.

(A) General. Guest rooms or guest suites in hotels, motels, sleeping rooms in dormitories, and similar occupancies shall have receptacle outlets installed in accordance with 210.52(A) and (D). Guest rooms or guest suites provided with permanent provisions for cooking shall have receptacle outlets installed in accordance with all of the applicable rules in 210.52.

(B) Receptacle Placement. In applying the provisions of 210.52(A), the total number of receptacle outlets shall not be less than the minimum number that would comply with the provisions of that section. These receptacle outlets shall be permitted to be located conveniently for permanent furniture layout. At least two receptacle outlets shall be readily accessible. Where receptacles are installed behind the bed, the receptacle shall be located to prevent the bed from contacting any attachment plug that may be installed or the receptacle shall be provided with a suitable guard.

210.62 Show Windows. At least one receptacle outlet shall be installed within 450 mm (18 in.) of the top of a show window for each 3.7 linear m (12 linear ft) or major fraction thereof of show window area measured horizontally at its maximum width.

210.63 Heating, Air-Conditioning, and Refrigeration Equipment Outlet. A 125-volt, single-phase, 15- or 20-ampere-rated receptacle outlet shall be installed at an accessible location for the servicing of heating, air-conditioning, and refrigeration equipment. The receptacle shall be located on the same level and within 7.5 m (25 ft) of the heating, air-conditioning, and refrigeration equipment. The receptacle outlet shall not be connected to the load side of the equipment disconnecting means.

Exception: A receptacle outlet shall not be required at one- and two-family dwellings for the service of evaporative coolers.

Informational Note: See 210.8 for ground-fault circuit-interrupter requirements.

210.70 Lighting Outlets Required. Lighting outlets shall be installed where specified in 210.70(A), (B), and (C).

(A) Dwelling Units. In dwelling units, lighting outlets shall be installed in accordance with 210.70(A)(1), (A)(2), and (A)(3).

(1) Habitable Rooms. At least one wall switch-controlled lighting outlet shall be installed in every habitable room and bathroom.

Exception No. 1: In other than kitchens and bathrooms, one or more receptacles controlled by a wall switch shall be permitted in lieu of lighting outlets.

Exception No. 2: Lighting outlets shall be permitted to be controlled by occupancy sensors that are (1) in addition to wall switches or (2) located at a customary wall switch location and equipped with a manual override that will allow the sensor to function as a wall switch.

(2) Additional Locations. Additional lighting outlets shall be installed in accordance with (A)(2)(a), (A)(2)(b), and (A)(2)(c).

(a) At least one wall switch-controlled lighting outlet shall be installed in hallways, stairways, attached garages, and detached garages with electric power.

(b) For dwelling units, attached garages, and detached garages with electric power, at least one wall switch-controlled lighting outlet shall be installed to provide illumination on the exterior side of outdoor entrances or exits with grade level access. A vehicle door in a garage shall not be considered as an outdoor entrance or exit.

(c) Where one or more lighting outlet(s) are installed for interior stairways, there shall be a wall switch at each floor level, and landing level that includes an entryway, to control the lighting outlet(s) where the stairway between floor levels has six risers or more.

Exception to (A)(2)(a), (A)(2)(b), and (A)(2)(c): In hallways, in stairways, and at outdoor entrances, remote, central, or automatic control of lighting shall be permitted.

(3) Storage or Equipment Spaces. For attics, underfloor spaces, utility rooms, and basements, at least one lighting outlet containing a switch or controlled by a wall switch shall be installed where these spaces are used for storage or

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contain equipment requiring servicing. At least one point of control shall be at the usual point of entry to these spaces. The lighting outlet shall be provided at or near the equipment requiring servicing.

(B) Guest Rooms or Guest Suites. In hotels, motels, or similar occupancies, guest rooms or guest suites shall have at least one wall switch-controlled lighting outlet installed in every habitable room and bathroom.

Exception No. 1: In other than bathrooms and kitchens where provided, one or more receptacles controlled by a wall switch shall be permitted in lieu of lighting outlets.

Exception No. 2: Lighting outlets shall be permitted to be controlled by occupancy sensors that are (1) in addition to wall switches or (2) located at a customary wall switch location and equipped with a manual override that allows the sensor to function as a wall switch.

(C) Other Than Dwelling Units. For attics and underfloor spaces containing equipment requiring servicing, such as heating, air-conditioning, and refrigeration equipment, at least one lighting outlet containing a switch or controlled by a wall switch shall be installed in such spaces. At least one point of control shall be at the usual point of entry to these spaces. The lighting outlet shall be provided at or near the equipment requiring servicing.

ARTICLE 215
Feeders

215.1 Scope. This article covers the installation requirements, overcurrent protection requirements, minimum size, and ampacity of conductors for feeders supplying branch-circuit loads.

Exception: Feeders for electrolytic cells as covered in 668.3(C)(1) and (C)(4).

215.2 Minimum Rating and Size.

(A) Feeders Not More Than 600 Volts.

(1) General. Feeder conductors shall have an ampacity not less than required to supply the load as calculated in Parts III, IV, and V of Article 220. The minimum feeder-circuit conductor size, before the application of any adjustment or correction factors, shall have an allowable ampacity not less than the noncontinuous load plus 125 percent of the continuous load.

Exception No. 1: If the assembly, including the overcurrent devices protecting the feeder(s), is listed for operation at 100 percent of its rating, the allowable ampacity of the feeder conductors shall be permitted to be not less than the sum of the continuous load plus the noncontinuous load.

Exception No. 2: Grounded conductors that are not connected to an overcurrent device shall be permitted to be sized at 100 percent of the continuous and noncontinuous load.

(2) Grounded Conductor. The size of the feeder circuit grounded conductor shall not be smaller than that required by 250.122, except that 250.122(F) shall not apply where grounded conductors are run in parallel.

Additional minimum sizes shall be as specified in 215.2(A)(2) and (A)(3) under the conditions stipulated.

(3) Ampacity Relative to Service Conductors. The feeder conductor ampacity shall not be less than that of the service conductors where the feeder conductors carry the total load supplied by service conductors with an ampacity of 55 amperes or less.

(4) Individual Dwelling Unit or Mobile Home Conductors. Feeder conductors for individual dwelling units or mobile homes need not be larger than service conductors. Paragraph 310.15(B)(6) shall be permitted to be used for conductor size.

Informational Note No. 1: See Examples D1 through D11 in Informative Annex D.

Informational Note No. 2: Conductors for feeders as defined in Article 100, sized to prevent a voltage drop exceeding 3 percent at the farthest outlet of power, heating, and lighting loads, or combinations of such loads, and where the maximum total voltage drop on both feeders and branch circuits to the farthest outlet does not exceed 5 percent, will provide reasonable efficiency of operation.

Informational Note No. 3: See 210.19(A), Informational Note No. 4, for voltage drop for branch circuits.

(B) Feeders over 600 Volts. The ampacity of conductors shall be in accordance with 310.15 and 310.60 as applicable. Where installed, the size of the feeder-circuit grounded conductor shall not be smaller than that required by 250.122, except that 250.122(F) shall not apply where grounded conductors are run in parallel. Feeder conductors over 600 volts shall be sized in accordance with 215.2(B)(1), (B)(2), or (B)(3).

(1) Feeders Supplying Transformers. The ampacity of feeder conductors shall not be less than the sum of the nameplate ratings of the transformers supplied when only transformers are supplied.

(2) Feeders Supplying Transformers and Utilization Equipment. The ampacity of feeders supplying a combination of transformers and utilization equipment shall not be less than the sum of the nameplate ratings of the transformers and 125 percent of the designed potential load of the utilization equipment that will be operated simultaneously.

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(3) Supervised Installations. For supervised installations, feeder conductor sizing shall be permitted to be determined by qualified persons under engineering supervision. Supervised installations are defined as those portions of a facility where all of the following conditions are met:

  1. Conditions of design and installation are provided under engineering supervision.
  2. Qualified persons with documented training and experience in over 600-volt systems provide maintenance, monitoring, and servicing of the system.

215.3 Overcurrent Protection. Feeders shall be protected against overcurrent in accordance with the provisions of Part I of Article 240. Where a feeder supplies continuous loads or any combination of continuous and noncontinuous loads, the rating of the overcurrent device shall not be less than the noncontinuous load plus 125 percent of the continuous load.

Exception No. 1: Where the assembly, including the over-current devices protecting the feeder(s), is listed for operation at 100 percent of its rating, the ampere rating of the overcurrent device shall be permitted to be not less than the sum of the continuous load plus the noncontinuous load.

Exception No. 2: Overcurrent protection for feeders over 600 volts, nominal, shall comply with Part IX of Article 240.

215.4 Feeders with Common Neutral Conductor.

(A) Feeders with Common Neutral. Up to three sets of 3-wire feeders or two sets of 4-wire or 5-wire feeders shall be permitted to utilize a common neutral.

(B) In Metal Raceway or Enclosure. Where installed in a metal raceway or other metal enclosure, all conductors of all feeders using a common neutral conductor shall be enclosed within the same raceway or other enclosure as required in 300.20.

215.5 Diagrams of Feeders. If required by the authority having jurisdiction, a diagram showing feeder details shall be provided prior to the installation of the feeders. Such a diagram shall show the area in square feet of the building or other structure supplied by each feeder, the total calculated load before applying demand factors, the demand factors used, the calculated load after applying demand factors, and the size and type of conductors to be used.

215.6 Feeder Equipment Grounding Conductor. Where a feeder supplies branch circuits in which equipment grounding conductors are required, the feeder shall include or provide an equipment grounding conductor in accordance with the provisions of 250.134, to which the equipment grounding conductors of the branch circuits shall be connected. Where the feeder supplies a separate building or structure, the requirements of 250.32(B) shall apply.

215.7 Ungrounded Conductors Tapped from Grounded Systems. Two-wire dc circuits and ac circuits of two or more ungrounded conductors shall be permitted to be tapped from the ungrounded conductors of circuits having a grounded neutral conductor. Switching devices in each tapped circuit shall have a pole in each ungrounded conductor.

215.9 Ground-Fault Circuit-Interrupter Protection for Personnel. Feeders supplying 15- and 20-ampere receptacle branch circuits shall be permitted to be protected by a ground-fault circuit interrupter in lieu of the provisions for such interrupters as specified in 210.8 and 590.6(A).

215.10 Ground-Fault Protection of Equipment. Each feeder disconnect rated 1000 amperes or more and installed on solidly grounded wye electrical systems of more than 150 volts to ground, but not exceeding 600 volts phase-to-phase, shall be provided with ground-fault protection of equipment in accordance with the provisions of 230.95.

Informational Note: For buildings that contain health care occupancies, see the requirements of 517.17.

Exception No. 1: The provisions of this section shall not apply to a disconnecting means for a continuous industrial process where a nonorderly shutdown will introduce additional or increased hazards.

Exception No. 2: The provisions of this section shall not apply if ground-fault protection of equipment is provided on the supply side of the feeder and on the load side of any transformer supplying the feeder.

215.11 Circuits Derived from Autotransformers. Feeders shall not be derived from autotransformers unless the system supplied has a grounded conductor that is electrically connected to a grounded conductor of the system supplying the autotransformer.

Exception No. 1: An autotransformer shall be permitted without the connection to a grounded conductor where transforming from a nominal 208 volts to a nominal 240-volt supply or similarly from 240 volts to 208 volts.

Exception No. 2: In industrial occupancies, where conditions of maintenance and supervision ensure that only qualified persons service the installation, autotransformers shall be permitted to supply nominal 600-volt loads from nominal 480-volt systems, and 480-volt loads from nominal 600-volt systems, without the connection to a similar grounded conductor.

215.12 Identification for Feeders.

(A) Grounded Conductor. The grounded conductor of a feeder shall be identified in accordance with 200.6.

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(B) Equipment Grounding Conductor. The equipment grounding conductor shall be identified in accordance with 250.119.

(C) Ungrounded Conductors. Where the premises wiring system has feeders supplied from more than one nominal voltage system, each ungrounded conductor of a feeder shall be identified by phase or line and system at all termination, connection, and splice points. The means of identification shall be permitted to be by separate color coding, marking tape, tagging, or other approved means. The method utilized for conductors originating within each feeder panel board or similar feeder distribution equipment shall be documented in a manner that is readily available or shall be permanently posted at each feeder panelboard or similar feeder distribution equipment.

ARTICLE 220
Branch-Circuit, Feeder, and Service Calculations

I. General

220.1 Scope. This article provides requirements for calculating branch-circuit, feeder, and service loads. Part I provides for general requirements for calculation methods. Part II provides calculation methods for branch-circuit loads. Parts III and IV provide calculation methods for feeders and services. Part V provides calculation methods for farms.

Informational Note: See Figure 220.1 for information on the organization of Article 220.

220.3 Application of Other Articles. In other articles applying to the calculation of loads in specialized applications, there are requirements provided in Table 220.3 that are in addition to, or modifications of, those within this article.

220.5 Calculations.

(A) Voltages. Unless other voltages are specified, for purposes of calculating branch-circuit and feeder loads, nominal system voltages of 120, 120/240, 208Y/120, 240, 347, 480Y/277, 480, 600Y/347, and 600 volts shall be used.

(B) Fractions of an Ampere. Calculations shall be permitted to be rounded to the nearest whole ampere, with decimal fractions smaller than 0.5 dropped.

II. Branch-Circuit Load Calculations

220.10 General. Branch-circuit loads shall be calculated as shown in 220.12, 220.14, and 220.16.

Figure 220.1 Branch-Circuit, Feeder, and Service Calculation Methods.

Figure 220.1 Branch-Circuit, Feeder, and Service Calculation Methods.

220.12 Lighting Load for Specified Occupancies. A unit load of not less than that specified in Table 220.12 for occupancies specified therein shall constitute the minimum lighting load. The floor area for each floor shall be calculated from the outside dimensions of the building, dwelling unit, or other area involved. For dwelling units, the calculated floor area shall not include open porches, garages, or unused or unfinished spaces not adaptable for future use.

Informational Note: The unit values herein are based on minimum load conditions and 100 percent power factor and may not provide sufficient capacity for the installation contemplated.

220.14 Other Loads — All Occupancies. In all occupancies, the minimum load for each outlet for general-use receptacles and outlets not used for general illumination shall not be less than that calculated in 220.14(A) through (L), the loads shown being based on nominal branch-circuit voltages.

Exception: The loads of outlets serving switchboards and switching frames in telephone exchanges shall be waived from the calculations.

(A) Specific Appliances or Loads. An outlet for a specific appliance or other load not covered in 220.14(B) through (L) shall be calculated based on the ampere rating of the appliance or load served.

(B) Electric Dryers and Electric Cooking Appliances in Dwelling Units. Load calculations shall be permitted as specified in 220.54 for electric dryers and in 220.55 for electric ranges and other cooking appliances.

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Table 220.3 Additional Load Calculation References
Calculation Article Section (or Part)
Air-conditioning and refrigerating equipment, branch-circuit conductor sizing 440 Part IV
Cranes and hoists, rating and size of conductors 610 610.14
Electric welders, ampacity calculations 630 630.11, 630.31
Electrically driven or controlled irrigation machines 675 675.7(A), 675.22(A)
Electrified truck parking space 626  
Electrolytic cell lines 668 668.3(C)
Electroplating, branch-circuit conductor sizing 669 669.5
Elevator feeder demand factors 620 620.14
Fire pumps, voltage drop (mandatory calculation) 695 695.7
Fixed electric heating equipment for pipelines and vessels, branch-circuit sizing 427 427.4
Fixed electric space-heating equipment, branch-circuit sizing 424 424.3
Fixed outdoor electric deicing and snow-melting equipment, branch-circuit sizing 426 426.4
Industrial machinery, supply conductor sizing 670 670.4(A)
Marinas and boatyards, feeder and service load calculations 555 555.12
Mobile homes, manufactured homes, and mobile home parks, total load for determining power supply 550 550.18(B)
Mobile homes, manufactured homes, and mobile home parks,
allowable demand factors for park electrical wiring systems
550 550.31
Motion picture and television studios and similar locations - sizing of feeder
conductors for television studio sets
530 530.19
Motors, feeder demand factor 430 430.26
Motors, multimotor and combination-load equipment 430 430.25
Motors, several motors or a motor(s) and other load(s) 430 430.24
Over 600-volt branch-circuit calculations 210 210.19(B)
Over 600-volt feeder calculations 215 215.2(B)
Phase converters, conductors 455 455.6
Recreational vehicle parks, basis of calculations 551 551.73(A)
Sensitive electrical equipment, voltage drop (mandatory calculation) 647 647.4(D)
Solar photovoltaic systems, circuit sizing and current 690 690.8
Storage-type water heaters 422 422.11(E)
Theaters, stage switchboard feeders 520 520.27

(C) Motor Loads. Outlets for motor loads shall be calculated in accordance with the requirements in 430.22, 430.24, and 440.6.

(D) Luminaires. An outlet supplying luminaire(s) shall be calculated based on the maximum volt-ampere rating of the equipment and lamps for which the luminaire(s) is rated.

(E) Heavy-Duty Lampholders. Outlets for heavy-duty lampholders shall be calculated at a minimum of 600 volt-amperes.

(F) Sign and Outline Lighting. Sign and outline lighting outlets shall be calculated at a minimum of 1200 volt-amperes for each required branch circuit specified in 600.5(A).

(G) Show Windows. Show windows shall be calculated in accordance with either of the following:

  1. The unit load per outlet as required in other provisions of this section
  2. At 200 volt-amperes per 300 mm (1 ft) of show window
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Table 220.12 General Lighting Loads by Occupancy
  Unit Load
Type of Occupancy Volt-Amperes/Square Meter Volt-Amperes/Square Foot
Armories and auditoriums 11 1
Banks 39b b
Barber shops and beauty parlors 33 3
Churches 11 1
Clubs 22 2
Court rooms 22 2
Dwelling unitsa 33 3
Garages — commercial (storage) 6 ½
Hospitals 22 2
Hotels and motels, including apartment
houses without provision for cooking by tenantsa
22 2
Industrial commercial (loft) buildings 22 2
Lodge rooms 17
Office buildings 39b b
Restaurants 22 2
Schools 33 3
Stores 33 3
Warehouses (storage) 3 ¼
In any of the preceding occupancies except one-family dwellings and individual
dwelling units of two-family and multifamily dwellings:
   
  Assembly halls and auditoriums 11 1
  Halls, corridors, closets, stairways 6 ½
  Storage spaces 3 ¼
aSee 220.14(J).
bSee 220.14(K).

(H) Fixed Multioutlet Assemblies. Fixed multioutlet assemblies used in other than dwelling units or the guest rooms or guest suites of hotels or motels shall be calculated in accordance with (H)(1) or (H)(2). For the purposes of this section, the calculation shall be permitted to be based on the portion that contains receptacle outlets.

  1. Where appliances are unlikely to be used simultaneously, each 1.5 m (5 ft) or fraction thereof of each separate and continuous length shall be considered as one outlet of not less than 180 volt-amperes.
  2. Where appliances are likely to be used simultaneously, each 300 mm (1 ft) or fraction thereof shall be considered as an outlet of not less than 180 volt-amperes.

(I) Receptacle Outlets. Except as covered in 220.14(J) and (K), receptacle outlets shall be calculated at not less than 180 volt-amperes for each single or for each multiple receptacle on one yoke. A single piece of equipment consisting of a multiple receptacle comprised of four or more receptacles shall be calculated at not less than 90 volt-amperes pet-receptacle. This provision shall not be applicable to the receptacle outlets specified in 210.11(C)(1) and (C)(2).

(J) Dwelling Occupancies. In one-family, two-family, and multifamily dwellings and in guest rooms or guest suites of hotels and motels, the outlets specified in (J)(1), (J)(2), and (J)(3) are included in the general lighting load calculations of 220.12. No additional load calculations shall be required for such outlets.

  1. All general-use receptacle outlets of 20-ampere rating or less, including receptacles connected to the circuits in 210.11(C)(3)
  2. The receptacle outlets specified in 210.52(E) and (G)
  3. The lighting outlets specified in 210.70(A) and (B)

(K) Banks and Office Buildings. In banks or office buildings, the receptacle loads shall be calculated to be the larger of (1) or (2):

  1. The calculated load from 220.14(I)
  2. 11 volt-amperes/m2 or 1 volt-ampere/ft2

(L) Other Outlets. Other outlets not covered in 220.14(A) through (K) shall be calculated based on 180 volt-amperes per outlet.

220.16 Loads for Additions to Existing Installations.

(A) Dwelling Units. Loads added to an existing dwelling unit(s) shall comply with the following as applicable:

  1. Loads for structural additions to an existing dwelling unit or for a previously unwired portion of an existing dwelling unit, either of which exceeds 46.5 m2 (500 ft2), shall be calculated in accordance with 220.12 and 220.14.
  2. Loads for new circuits or extended circuits in previously wired dwelling units shall be calculated in accordance with either 220.12 or 220.14, as applicable.

(B) Other Than Dwelling Units. Loads for new circuits or extended circuits in other than dwelling units shall be calculated in accordance with either 220.12 or 220.14, as applicable.

220.18 Maximum Loads. The total load shall not exceed the rating of the branch circuit, and it shall not exceed the maximum loads specified in 220.18(A) through (C) under the conditions specified therein.

(A) Motor-Operated and Combination Loads. Where a circuit supplies only motor-operated loads, Article 430 shall apply. Where a circuit supplies only air-conditioning equipment, refrigerating equipment, or both, Article 440 shall apply.

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For circuits supplying loads consisting of motor-operated utilization equipment that is fastened in place and has a motor larger than ⅛ hp in combination with other loads, the total calculated load shall be based on 125 percent of the largest motor load plus the sum of the other loads.

(B) Inductive and LED Lighting Loads. For circuits supplying lighting units that have ballasts, transformers, autotransformers, or LED drivers, the calculated load shall be based on the total ampere ratings of such units and not on the total watts of the lamps.

(C) Range Loads. It shall be permissible to apply demand factors for range loads in accordance with Table 220.55, including Note 4.

III. Feeder and Service Load Calculations

220.40 General. The calculated load of a feeder or service shall not be less than the sum of the loads on the branch circuits supplied, as determined by Part II of this article, after any applicable demand factors permitted by Part III or IV or required by Part V have been applied.

Informational Note: See Examples Dl(a) through D10 in Informative Annex D. See 220.18(B) for the maximum load in amperes permitted for lighting units operating at less than 100 percent power factor.

220.42 General Lighting. The demand factors specified in Table 220.42 shall apply to that portion of the total branch-circuit load calculated for general illumination. They shall not be applied in determining the number of branch circuits for general illumination.

220.43 Show-Window and Track Lighting.

(A) Show Windows. For show-window lighting, a load of not less than 660 volt-amperes/linear meter or 200 volt-amperes/linear foot shall be included for a show window, measured horizontally along its base.

Informational Note: See 220.14(G) for branch circuits supplying show windows.

(B) Track Lighting. For track lighting in other than dwelling units or guest rooms or guest suites of hotels or motels, an additional load of 150 volt-amperes shall be included for every 600 mm (2 ft) of lighting track or fraction thereof. Where multicircuit track is installed, the load shall be considered to be divided equally between the track circuits.

Exception: If the track lighting is supplied through a device that limits the current to the track, the load shall be permitted to be calculated based on the rating of the device used to limit the current.

Table 220.42 Lighting Load Demand Factors
Type of Occupancy Portion of Lighting Load to Which
Demand Factor Applies (Volt-Amperes)
Demand Factor (%)
Dwelling units First 3000 or less at 100
From 3001 to 120,000 at 35
Remainder over 120,000 at 25
Hospitals* First 50,000 or less at 40
Remainder over 50,000 at 20
Hotels and motels, including apartment houses
without provision for cooking by tenants*
First 20,000 or less at 50
From 20,001 to 100,000 at 40
Remainder over 100,000 at 30
Warehouses (storage) First 12,500 or less at 100
Remainder over 12,500 at 50
All others Total volt-amperes 100
*The demand factors of this table shall not apply to the calculated load of feeders or services supplying areas in hospitals, hotels, and motels where the entire lighting is likely to be used at one time, as in operating rooms, ballrooms, or dining rooms.

220.44 Receptacle Loads — Other Than Dwelling Units. Receptacle loads calculated in accordance with 220.14(H) and (I) shall be permitted to be made subject to the demand factors given in Table 220.42 or Table 220.44.

Table 220.44 Demand Factors for Non-Dwelling Receptacle Loads
Portion of Receptacle Load to Which Demand Factor Applies (Volt-Amperes) Demand Factor (%)
First 10 kVA or less at 100
Remainder over 10 kVA at 50

220.50 Motors. Motor loads shall be calculated in accordance with 430.24, 430.25, and 430.26 and with 440.6 for hermetic refrigerant motor compressors.

220.51 Fixed Electric Space Heating. Fixed electric space-heating loads shall be calculated at 100 percent of the total connected load. However, in no case shall a feeder or service load current rating be less than the rating of the largest branch circuit supplied.

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Exception: Where reduced loading of the conductors results from units operating on duty-cycle, intermittently, or from all units not operating at the same time, the authority having jurisdiction may grant permission for feeder and service conductors to have an ampacity less than 100 percent, provided the conductors have an ampacity for the load so determined.

220.52 Small-Appliance and Laundry Loads — Dwelling Unit.

(A) Small-Appliance Circuit Load. In each dwelling unit, the load shall be calculated at 1500 volt-amperes for each 2-wire small-appliance branch circuit as covered by 210.11(C)(1). Where the load is subdivided through two or more feeders, the calculated load for each shall include not less than 1500 volt-amperes for each 2-wire small-appliance branch circuit. These loads shall be permitted to be included with the general lighting load and subjected to the demand factors provided in Table 220.42.

Exception: The individual branch circuit permitted by 210.52(B)(1), Exception No. 2, shall be permitted to be excluded from the calculation required by 220.52.

(B) Laundry Circuit Load. A load of not less than 1500 volt-amperes shall be included for each 2-wire laundry branch circuit installed as covered by 210.11(C)(2). This load shall be permitted to be included with the general lighting load and subjected to the demand factors provided in Table 220.42.

220.53 Appliance Load — Dwelling Unit(s). It shall be permissible to apply a demand factor of 75 percent to the nameplate rating load of four or more appliances fastened in place, other than electric ranges, clothes dryers, space-heating equipment, or air-conditioning equipment, that are served by the same feeder or service in a one-family, two-family, or multifamily dwelling.

220.54 Electric Clothes Dryers — Dwelling Unit(s). The load for household electric clothes dryers in a dwelling unit(s) shall be either 5000 watts (volt-amperes) or the nameplate rating, whichever is larger, for each dryer served. The use of the demand factors in Table 220.54 shall be permitted. Where two or more single-phase dryers are supplied by a 3-phase, 4-wire feeder or service, the total load shall be calculated on the basis of twice the maximum number connected between any two phases. Kilovolt-amperes (kVA) shall be considered equivalent to kilowatts (kW) for loads calculated in this section.

220.55 Electric Ranges and Other Cooking Appliances — Dwelling Unit(s). The load for household electric ranges, wall-mounted ovens, counter-mounted cooking units, and other household cooking appliances individually rated in excess of 1¾ kW shall be permitted to be calculated in accordance with Table 220.55. Kilovolt-amperes (kVA) shall be considered equivalent to kilowatts (kW) for loads calculated under this section.

Table 220.54 Demand Factors for Household Electric Clothes Dryers
Number of Dryers Demand Factor (%)
1-4 100
5 85
6 75
7 65
8 60
9 55
10 50
11 47
12-23 47% minus 1% for each dryer exceeding 11
24-42 35% minus 0.5% for each dryer exceeding 23
43 and over 25%

Where two or more single-phase ranges are supplied by a 3-phase, 4-wire feeder or service, the total load shall be calculated on the basis of twice the maximum number connected between any two phases.

Informational Note No. 1: See Example D5(A) in Informative Annex D.

Informational Note No. 2: See Table 220.56 for commercial cooking equipment.

Informational Note No. 3: See the examples in Informative Annex D.

220.56 Kitchen Equipment — Other Than Dwelling Unit(s). It shall be permissible to calculate the load for commercial electric cooking equipment, dishwasher booster heaters, water heaters, and other kitchen equipment in accordance with Table 220.56. These demand factors shall be applied to all equipment that has either thermostatic control or intermittent use as kitchen equipment. These demand factors shall not apply to space-heating, ventilating, or air-conditioning equipment.

However, in no case shall the feeder or service calculated load be less than the sum of the largest two kitchen equipment loads.

220.60 Noncoincident Loads. Where it is unlikely that two or more noncoincident loads will be in use simultaneously, it shall be permissible to use only the largest load(s) that will be used at one time for calculating the total load of a feeder or service.

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Table 220.55 Demand Factors and Loads for Household Electric Ranges, Wall-Mounted Ovens, Counter-Mounted Cooking Units, and Other Household Cooking Appliances over 1¾ kW Rating (Column C to be used in all cases except as otherwise permitted in Note 3.)
  Demand Factor (%) (See Notes)  
Number of Appliances Column A
(Less than 3½ kW Rating)
Column B
(3½ kW through 8¾ kW Rating)
Column C
Maximum Demand (kW) (See Notes)(Not over 12 kW Rating)
1
2
3
4
5
80
75
70
66
62
80
65
55
50
45
8
11
14
17
20
6
7
8
9
10
59
56
53
51
49
43
40
36
35
34
21
22
23
24
25
11
12
13
14
15
47
45
43
41
40
32
32
32
32
32
26
27
28
29
30
16
17
18
19
20
39
38
37
36
35
28
28
28
28
28
31
32
33
34
35
21
22
23
24
25
34
33
32
31
30
26
26
26
26
26
36
37
38
39
40
26-30
31-40
30
30
24
22
15 kW + 1 kW for each range
41-50
51-60
61 and over
30
30
30
20
18
16
25 kW + ¾ kW for each range
Notes:
1. Over 12 kW through 27 kW ranges all of same rating. For ranges individually rated more than 12 kW but not more than 27 kW, the maximum demand in Column C shall be increased 5 percent for each additional kilowatt of rating or major fraction thereof by which the rating of individual ranges exceeds 12 kW.
2. Over 8¾ kW through 27 kW ranges of unequal ratings. For ranges individually rated more than 8¾ kW and of different ratings, but none exceeding 27 kW, an average value of rating shall be calculated by adding together the ratings of all ranges to obtain the total connected load (using 12 kW for any range rated less than 12 kW) and dividing by the total number of ranges. Then the maximum demand in Column C shall be increased 5 percent for each kilowatt or major fraction thereof by which this average value exceeds 12 kW.
3. Over 1¾ kW through 8¾ kW. In lieu of the method provided in Column C, it shall be permissible to add the nameplate ratings of all household cooking appliances rated more than 1¾ kW but not more than 8¾ kW and multiply the sum by the demand factors specified in Column A or Column B for the given number of appliances. Where the rating of cooking appliances falls under both Column A and Column B, the demand factors for each column shall be applied to the appliances for that column, and the results added together.
4. Branch-Circuit Load. It shall be permissible to calculate the branch-circuit load for one range in accordance with Table 220.55. The branch-circuit load for one wall-mounted oven or one counter-mounted cooking unit shall be the nameplate rating of the appliance. The branch-circuit load for a counter-mounted cooking unit and not more than two wall-mounted ovens, all supplied from a single branch circuit and located in the same room, shall be calculated by adding the nameplate rating of the individual appliances and treating this total as equivalent to one range.
5. This table shall also apply to household cooking appliances rated over 1¾ kW and used in instructional programs.
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Table 220.56 Demand Factors for Kitchen Equipment — Other Than Dwelling Unit(s)
Number of Units of Equipment Demand Factor (%)
1
2
3
4
5
6 and over
100
100
90
80
70
65

220.61 Feeder or Service Neutral Load.

(A) Basic Calculation. The feeder or service neutral load shall be the maximum unbalance of the load determined by this article. The maximum unbalanced load shall be the maximum net calculated load between the neutral conductor and any one ungrounded conductor.

Exception: For 3-wire, 2-phase or 5-wire, 2-phase systems, the maximum unbalanced load shall be the maximum net calculated load between the neutral conductor and any one ungrounded conductor multiplied by 140 percent.

(B) Permitted Reductions. A service or feeder supplying the following loads shall be permitted to have an additional demand factor of 70 percent applied to the amount in 220.61(B)(1) or portion of the amount in 220.61(B)(2) determined by the basic calculation:

  1. A feeder or service supplying household electric ranges, wall-mounted ovens, counter-mounted cooking units, and electric dryers, where the maximum unbalanced load has been determined in accordance with Table 220.55 for ranges and Table 220.54 for dryers
  2. That portion of the unbalanced load in excess of 200 amperes where the feeder or service is supplied from a 3-wire dc or single-phase ac system; or a 4-wire, 3-phase, 3-wire, 2-phase system; or a 5-wire, 2-phase system

(C) Prohibited Reductions. There shall be no reduction of the neutral or grounded conductor capacity applied to the amount in 220.61(C)(1), or portion of the amount in (C)(2), from that determined by the basic calculation:

  1. Any portion of a 3-wire circuit consisting of 2 ungrounded conductors and the neutral conductor of a 4-wire, 3-phase, wye-connected system
  2. That portion consisting of nonlinear loads supplied from a 4-wire, wye-connected, 3-phase system

Informational Note No. 1: See Examples Dl(a), Dl(b), D2(b), D4(a), and D5(a) in Informative Annex D.

Informational Note No. 2: A 3-phase, 4-wire, wye-connected power system used to supply power to nonlinear loads may necessitate that the power system design allow for the possibility of high harmonic neutral-conductor currents.

IV. Optional Feeder and Service Load Calculations

220.80 General. Optional feeder and service load calculations shall be permitted in accordance with Part IV.

220.82 Dwelling Unit.

(A) Feeder and Service Load. This section applies to a dwelling unit having the total connected load served by a single 120/240-volt or 208Y/120-volt set of 3-wire service or feeder conductors with an ampacity of 100 or greater. It shall be permissible to calculate the feeder and service loads in accordance with this section instead of the method specified in Part III of this article. The calculated load shall be the result of adding the loads from 220.82(B) and (C). Feeder and service-entrance conductors whose calculated load is determined by this optional calculation shall be permitted to have the neutral load determined by 220.61.

(B) General Loads. The general calculated load shall be not less than 100 percent of the first 10 kVA plus 40 percent of the remainder of the following loads:

  1. 33 volt-amperes/m2 or 3 volt-amperes/ft2 for general lighting and general-use receptacles. The floor area for each floor shall be calculated from the outside dimensions of the dwelling unit. The calculated floor area shall not include open porches, garages, or unused or unfinished spaces not adaptable for future use.
  2. 1500 volt-amperes for each 2-wire, 20-ampere small-appliance branch circuit and each laundry branch circuit covered in 210.11(C)(1) and (C)(2).
  3. The nameplate rating of the following:
    1. All appliances that are fastened in place, permanently connected, or located to be on a specific circuit
    2. Ranges, wall-mounted ovens, counter-mounted cooking units
    3. Clothes dryers that are not connected to the laundry branch circuit specified in item (2)
    4. Water heaters
  4. The nameplate ampere or kVA rating of all permanently connected motors not included in item (3).

(C) Heating and Air-Conditioning Load. The largest of the following six selections (load in kVA) shall be included:

  1. 100 percent of the nameplate rating(s) of the air conditioning and cooling.
  2. 100 percent of the nameplate rating(s) of the heat pump when the heat pump is used without any supplemental electric heating.
  3. 100 percent of the nameplate rating(s) of the heat pump compressor and 65 percent of the supplemental electric heating for central electric space-heating systems. If the heat pump compressor is prevented from operating at 70-67 the same time as the supplementary heat, it does not need to be added to the supplementary heat for the total central space heating load.
  4. 65 percent of the nameplate rating(s) of electric space heating if less than four separately controlled units.
  5. 40 percent of the nameplate rating(s) of electric space heating if four or more separately controlled units.
  6. 100 percent of the nameplate ratings of electric thermal storage and other heating systems where the usual load is expected to be continuous at the full nameplate value. Systems qualifying under this selection shall not be calculated under any other selection in 220.82(C).

220.83 Existing Dwelling Unit. This section shall be permitted to be used to determine if the existing service or feeder is of sufficient capacity to serve additional loads. Where the dwelling unit is served by a 120/240-volt or 208Y/120-volt, 3-wire service, it shall be permissible to calculate the total load in accordance with 220.83(A) or (B).

(A) Where Additional Air-Conditioning Equipment or Electric Space-Heating Equipment Is Not to Be Installed. The following percentages shall be used for existing and additional new loads.

Load (kVA) Percent of Load
First 8 kVA of load at 100
Remainder of load at 40

Load calculations shall include the following:

  1. General lighting and general-use receptacles at 33 volt-amperes/m2 or 3 volt-amperes/ft2 as determined by 220.12
  2. 1500 volt-amperes for each 2-wire, 20-ampere small-appliance branch circuit and each laundry branch circuit covered in 210.11(C)(1) and (C)(2)
  3. The nameplate rating of the following:
    1. All appliances that are fastened in place, permanently connected, or located to be on a specific circuit
    2. Ranges, wall-mounted ovens, counter-mounted cooking units
    3. Clothes dryers that are not connected to the laundry branch circuit specified in item (2)
    4. Water heaters

(B) Where Additional Air-Conditioning Equipment or Electric Space-Heating Equipment Is to Be Installed.

The following percentages shall be used for existing and additional new loads. The larger connected load of air-conditioning or space-heating, but not both, shall be used.

Load Percent of Load
Air-conditioning equipment 100
Central electric space heating 100
Less than four separately controlled space-heating units 100
First 8 kVA of all other loads 100
Remainder of all other loads 40

Other loads shall include the following:

  1. General lighting and general-use receptacles at 33 volt-amperes/m2 or 3 volt-amperes/ft2 as determined by 220.12
  2. 1500 volt-amperes for each 2-wire, 20-ampere small-appliance branch circuit and each laundry branch circuit covered in 210.11(C)(1) and (C)(2)
  3. The nameplate rating of the following:
    1. All appliances that are fastened in place, permanently connected, or located to be on a specific circuit
    2. Ranges, wall-mounted ovens, counter-mounted cooking units
    3. Clothes dryers that are not connected to the laundry branch circuit specified in (2)
    4. Water heaters

220.84 Multifamily Dwelling.

(A) Feeder or Service Load. It shall be permissible to calculate the load of a feeder or service that supplies three or more dwelling units of a multifamily dwelling in accordance with Table 220.84 instead of Part III of this article if all the following conditions are met:

  1. No dwelling unit is supplied by more than one feeder.
  2. Each dwelling unit is equipped with electric cooking equipment.

    Exception: When the calculated load for multifamily dwellings without electric cooking in Part III of this article exceeds that calculated under Part IV for the identical load plus electric cooking (based on 8 kW per unit), the lesser of the two loads shall be permitted to be used.

  3. Each dwelling unit is equipped with either electric space heating or air conditioning, or both. Feeders and service conductors whose calculated load is determined by this optional calculation shall be permitted to have the neutral load determined by 220.61.

(B) House Loads. House loads shall be calculated in accordance with Part III of this article and shall be in addition to the dwelling unit loads calculated in accordance with Table 220.84.

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Table 220.84 Optional Calculations — Demand Factors for Three or More Multifamily Dwelling Units
Number of Dwelling Units Demand Factor (%)
3-5
6-7
8-10
45
44
43
11
12-13
14-15
16-17
18-20
42
41
40
39
38
21
22-23
24-25
26-27
28-30
37
36
35
34
33
31
32-33
34-36
37-38
39-42
32
31
30
29
28
43-45
46-50
51-55
56-61
62 and over
27
26
25
24
23

(C) Calculated Loads. The calculated load to which the demand factors of Table 220.84 apply shall include the following:

  1. 33 volt-amperes/m2 or 3 volt-amperes/ft2 for general lighting and general-use receptacles
  2. 1500 volt-amperes for each 2-wire, 20-ampere small-appliance branch circuit and each laundry branch circuit covered in 210.11(C)(1) and (C)(2)
  3. The nameplate rating of the following:
    1. All appliances that are fastened in place, permanently connected, or located to be on a specific circuit
    2. Ranges, wall-mounted ovens, counter-mounted cooking units
    3. Clothes dryers that are not connected to the laundry branch circuit specified in item (2)
    4. Water heaters
  4. The nameplate ampere or kVA rating of all permanently connected motors not included in item (3)
  5. The larger of the air-conditioning load or the fixed electric space-heating load

220.85 Two Dwelling Units. Where two dwelling units are supplied by a single feeder and the calculated load under Part III of this article exceeds that for three identical units calculated under 220.84, the lesser of the two loads shall be permitted to be used.

220.86 Schools. The calculation of a feeder or service load for schools shall be permitted in accordance with Table 220.86 in lieu of Part III of this article where equipped with electric space heating, air conditioning, or both. The connected load to which the demand factors of Table 220.86 apply shall include all of the interior and exterior lighting, power, water heating, cooking, other loads, and the larger of the air-conditioning load or space-heating load within the building or structure.

Feeders and service conductors whose calculated load is determined by this optional calculation shall be permitted to have the neutral load determined by 220.61. Where the building or structure load is calculated by this optional method, feeders within the building or structure shall have ampacity as permitted in Part III of this article; however, the ampacity of an individual feeder shall not be required to be larger than the ampacity for the entire building.

This section shall not apply to portable classroom buildings.

Table 220.86 Optional Method — Demand Factors for Feeders and Service Conductors for Schools
Connected Load Demand Factor (Percent)
First 33 VA/m2 Plus, (3 VA/ft2) at 100
Over 33 through 220 VA/m2 Plus, (3 through 20 VA/ft2) at 75
Remainder over 220 VA/m2 (20 VA/ft2) at 25

220.87 Determining Existing Loads. The calculation of a feeder or service load for existing installations shall be permitted to use actual maximum demand to determine the existing load under all of the following conditions:

  1. The maximum demand data is available for a 1-year period.

    Exception: If the maximum demand data for a 1 -year period is not available, the calculated load shall be permitted to be based on the maximum demand (measure of average power demand over a 15-minute period) continuously recorded over a minimum 30-day period using a recording ammeter or power meter connected to the highest loaded phase of the feeder or service, based on the initial loading at the start of the recording. The recording shall reflect the maximum demand of the feeder or service by being taken when the building or space is occupied and shall include by

    70-69

    measurement or calculation the larger of the heating or cooling equipment load, and other loads that may be periodic in nature due to seasonal or similar conditions.

  2. The maximum demand at 125 percent plus the new load does not exceed the ampacity of the feeder or rating of the service.
  3. The feeder has overcurrent protection in accordance with 240.4, and the service has overload protection in accordance with 230.90.

220.88 New Restaurants. Calculation of a service or feeder load, where the feeder serves the total load, for a new restaurant shall be permitted in accordance with Table 220.88 in lieu of Part III of this article.

The overload protection of the service conductors shall be in accordance with 230.90 and 240.4.

Feeder conductors shall not be required to be of greater ampacity than the service conductors.

Service or feeder conductors whose calculated load is determined by this optional calculation shall be permitted to have the neutral load determined by 220.61.

V. Farm Load Calculations

220.100 General. Farm loads shall be calculated in accordance with Part V.

220.102 Farm Loads — Buildings and Other Loads.

(A) Dwelling Unit. The feeder or service load of a farm dwelling unit shall be calculated in accordance with the provisions for dwellings in Part III or IV of this article. Where the dwelling has electric heat and the farm has electric grain-drying systems, Part IV of this article shall not be used to calculate the dwelling load where the dwelling and farm loads are supplied by a common service.

(B) Other Than Dwelling Unit. Where a feeder or service supplies a farm building or other load having two or more separate branch circuits, the load for feeders, service conductors, and service equipment shall be calculated in accordance with demand factors not less than indicated in Table 220.102.

Table 220.102 Method for Calculating Farm Loads for Other Than Dwelling Unit
Ampere Load at 240 Volts Maximum Demand Factor (%)
The greater of the following: All loads that are expected to operate
simultaneously, or 125 percent of the full load current of the largest motor, or First 60 amperes of the load
100
Next 60 amperes of all other loads 50
Remainder of other loads 25

220.103 Farm Loads — Total. Where supplied by a common service, the total load of the farm for service conductors and service equipment shall be calculated in accordance with the farm dwelling unit load and demand factors specified in Table 220.103. Where there is equipment in two or more farm equipment buildings or for loads having the same function, such loads shall be calculated in accordance with Table 220.102 and shall be permitted to be combined as a single load in Table 220.103 for calculating the total load.

Table 220.103 Method for Calculating Total Farm Load
Individual Loads Calculated in Accordance with Table 220.102 Demand Factor (%)
Largest load 100
Second largest load 75
Third largest load 65
Remaining loads 50
Note: To this total load, add the load of the farm dwelling unit calculated in accordance with Part III or IV of this article. Where the dwelling has electric heat and the farm has electric grain-drying systems, Part IV of this article shall not be used to calculate the dwelling load.

 

Table 220.88 Optional Method — Permitted Load Calculations for Service and Feeder Conductors for New Restaurants
Total Connected Load (kVA) All Electric Restaurant Calculated Loads (kVA) Not All Electric Restaurant Calculated Loads (kVA)
0-200
201-325
326-800
Over 800
80%
10% (amount over 200) + 160.0
50% (amount over 325) + 172.5
50% (amount over 800) + 410.0
100%
50% (amount over 200) + 200.0
45% (amount over 325) + 262.5
20% (amount over 800) + 476.3
Note: Add all electrical loads, including both heating and cooling loads, to calculate the total connected load. Select the one demand factor that applies from the table, then multiply the total connected load by this single demand factor.
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ARTICLE 225
Outside Branch Circuits and Feeders

225.1 Scope. This article covers requirements for outside branch circuits and feeders run on or between buildings, structures, or poles on the premises; and electrical equipment and wiring for the supply of utilization equipment that is located on or attached to the outside of buildings, structures, or poles.

Informational Note: For additional information on wiring over 600 volts, see ANSI C2-2007, National Electrical Safety Code.

225.2 Definition.

Substation. An enclosed assemblage of equipment (e.g., switches, circuit breakers, buses, and transformers) under the control of qualified persons, through which electric energy is passed for the purpose of switching or modifying its characteristics.

225.3 Other Articles. Application of other articles, including additional requirements to specific cases of equipment and conductors, is shown in Table 225.3.

I. General

225.4 Conductor Covering. Where within 3.0 m (10 ft) of any building or structure other than supporting poles or towers, open individual (aerial) overhead conductors shall be insulated or covered. Conductors in cables or raceways, except Type MI cable, shall be of the rubber-covered type or thermoplastic type and, in wet locations, shall comply with 310.10(C). Conductors for festoon lighting shall be of the rubber-covered or thermoplastic type.

Exception: Equipment grounding conductors and grounded circuit conductors shall be permitted to be bare or covered as specifically permitted elsewhere in this Code.

225.5 Size of Conductors 600 Volts, Nominal, or Less. The ampacity of outdoor branch-circuit and feeder conductors shall be in accordance with 310.15 based on loads as determined under 220.10 and Part III of Article 220.

225.6 Conductor Size and Support.

(A) Overhead Spans. Open individual conductors shall not be smaller than the following:

  1. For 600 volts, nominal, or less, 10 AWG copper or 8 AWG aluminum for spans up to 15 m (50 ft) in length, and 8 AWG copper or 6 AWG aluminum for a longer span unless supported by a messenger wire
  2. For over 600 volts, nominal, 6 AWG copper or 4 AWG aluminum where open individual conductors, and 8 AWG copper or 6 AWG aluminum where in cable
Table 225.3 Other Articles
Equipment/Conductors Article
Branch circuits 210
Class 1, Class 2, and Class 3 remote-control, signaling, and power-limited circuits 725
Communications circuits 800
Community antenna television and radio distribution systems 820
Conductors for general wiring 310
Electrically driven or controlled irrigation machines 675
Electric signs and outline lighting 600
Feeders 215
Fire alarm systems 760
Fixed outdoor electric deicing and snow-melting equipment 426
Floating buildings 553
Grounding and bonding 250
Hazardous (classified) locations 500
Hazardous (classified) locations—specific 510
Marinas and boatyards 555
Messenger-supported wiring 396
Mobile homes, manufactured homes, and mobile home parks 550
Open wiring on insulators 398
Over 600 volts, general 490
Overcurrent protection 240
Radio and television equipment 810
Services 230
Solar photovoltaic systems 690
Swimming pools, fountains, and similar installations 680
Use and identification of grounded conductors 200

(B) Festoon Lighting. Overhead conductors for festoon lighting shall not be smaller than 12 AWG unless the conductors are supported by messenger wires. In all spans exceeding 12 m (40 ft), the conductors shall be supported by messenger wire. The messenger wire shall be supported by strain insulators. Conductors or messenger wires shall not be attached to any fire escape, downspout, or plumbing equipment.

225.7 Lighting Equipment Installed Outdoors.

(A) General. For the supply of lighting equipment installed outdoors, the branch circuits shall comply with Article 210 and 225.7(B) through (D).

(B) Common Neutral. The ampacity of the neutral conductor shall not be less than the maximum net calculated load

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current between the neutral conductor and all ungrounded conductors connected to any one phase of the circuit.

(C) 277 Volts to Ground. Circuits exceeding 120 volts, nominal, between conductors and not exceeding 277 volts, nominal, to ground shall be permitted to supply luminaires for illumination of outdoor areas of industrial establishments, office buildings, schools, stores, and other commercial or public buildings.

(D) 600 Volts Between Conductors. Circuits exceeding 277 volts, nominal, to ground and not exceeding 600 volts, nominal, between conductors shall be permitted to supply the auxiliary equipment of electric-discharge lamps in accordance with 210.6(D)(1).

225.8 Calculation of Loads 600 Volts, Nominal, or Less.

(A) Branch Circuits. The load on outdoor branch circuits shall be as determined by 220.10.

(B) Feeders. The load on outdoor feeders shall be as determined by Part III of Article 220.

225.10 Wiring on Buildings. The installation of outside wiring on surfaces of buildings shall be permitted for circuits of not over 600 volts, nominal, as open wiring on insulators, as multiconductor cable, as Type MC cable, as Type UF cable, as Type MI cable, as messenger-supported wiring, in rigid metal conduit, in intermediate metal conduit, in rigid polyvinyl chloride (PVC) conduit, in reinforced thermosetting resin conduit (RTRC), in cable trays, as cablebus, in wireways, in auxiliary gutters, in electrical metallic tubing, in flexible metal conduit, in liquidtight flexible metal conduit, in liquidtight flexible nonmetallic conduit, and in busways. Circuits of over 600 volts, nominal, shall be installed as provided in 300.37.

225.11 Circuit Exits and Entrances. Where outside branch and feeder circuits leave or enter a building, the requirements of 230.52 and 230.54 shall apply.

225.12 Open-Conductor Supports. Open conductors shall be supported on glass or porcelain knobs, racks, brackets, or strain insulators.

225.14 Open-Conductor Spacings.

(A) 600 Volts, Nominal, or Less. Conductors of 600 volts, nominal, or less, shall comply with the spacings provided in Table 230.51(C).

(B) Over 600 Volts, Nominal. Conductors of over 600 volts, nominal, shall comply with the spacings provided in 110.36 and 490.24.

(C) Separation from Other Circuits. Open conductors shall be separated from open conductors of other circuits or systems by not less than 100 mm (4 in.).

(D) Conductors on Poles. Conductors on poles shall have a separation of not less than 300 mm (1 ft) where not placed on racks or brackets. Conductors supported on poles shall provide a horizontal climbing space not less than the following:

  1. Power conductors below communications conductors — 750 mm (30 in.)
  2. Power conductors alone or above communications conductors:
    1. 300 volts or less — 600 mm (24 in.)
    2. Over 300 volts — 750 mm (30 in.)
  3. Communications conductors below power conductors — same as power conductors
  4. Communications conductors alone — no requirement

225.15 Supports over Buildings. Supports over a building shall be in accordance with 230.29.

225.16 Attachment to Buildings.

(A) Point of Attachment. The point of attachment to a building shall be in accordance with 230.26.

(B) Means of Attachment. The means of attachment to a building shall be in accordance with 230.27.

225.17 Masts as Supports. Where a mast is used for the support of final spans of feeders or branch circuits, it shall be of adequate strength or be supported by braces or guys to withstand safely the strain imposed by the overhead drop. Where raceway-type masts are used, all raceway fittings shall be identified for use with masts. Only the feeder or branch-circuit conductors specified within this section shall be permitted to be attached to the feeder and/or branch-circuit mast.

225.18 Clearance for Overhead Conductors and Cables. Overhead spans of open conductors and open multiconductor cables of not over 600 volts, nominal, shall have a clearance of not less than the following:

  1. 3.0 m (10 ft) — above finished grade, sidewalks, or from any platform or projection from which they might be reached where the voltage does not exceed 150 volts to ground and accessible to pedestrians only
  2. 3.7 m (12 ft) — over residential property and driveways, and those commercial areas not subject to truck traffic where the voltage does not exceed 300 volts to ground
  3. 4.5 m (15 ft) — for those areas listed in the 3.7-m (12-ft) classification where the voltage exceeds 300 volts to ground 70-72
  4. 5.5 m (18 ft) — over public streets, alleys, roads, parking areas subject to truck traffic, driveways on other than residential property, and other land traversed by vehicles, such as cultivated, grazing, forest, and orchard
  5. 7.5 m (24.5 ft) — over track rails of railroads

225.19 Clearances from Buildings for Conductors of Not over 600 Volts, Nominal.

(A) Above Roofs. Overhead spans of open conductors and open multiconductor cables shall have a vertical clearance of not less than 2.5 m (8 ft) above the roof surface. The vertical clearance above the roof level shall be maintained for a distance not less than 900 mm (3 ft) in all directions from the edge of the roof.

Exception No. 1: The area above a roof surface subject to pedestrian or vehicular traffic shall have a vertical clearance from the roof surface in accordance with the clearance requirements of 225.18.

Exception No. 2: Where the voltage between conductors does not exceed 300, and the roof has a slope of 100 mm in 300 mm (4 in. in 12 in.) or greater, a reduction in clearance to 900 mm (3 ft) shall be permitted.

Exception No. 3: Where the voltage between conductors does not exceed 300, a reduction in clearance above only the overhanging portion of the roof to not less than 450 mm (18 in.) shall be permitted if (1) not more than 1.8 m (6 ft) of the conductors, 1.2 m (4 ft) horizontally, pass above the roof overhang and (2) they are terminated at a through-the-roof raceway or approved support.

Exception No. 4: The requirement for maintaining the vertical clearance 900 mm (3 ft) from the edge of the roof shall not apply to the final conductor span where the conductors are attached to the side of a building.

(B) From Nonbuilding or Nonbridge Structures. From signs, chimneys, radio and television antennas, tanks, and other nonbuilding or nonbridge structures, clearances — vertical, diagonal, and horizontal — shall not be less than 900 mm (3 ft).

(C) Horizontal Clearances. Clearances shall not be less than 900 mm (3 ft).

(D) Final Spans. Final spans of feeders or branch circuits shall comply with 225.19(D)(1), (D)(2), and (D)(3).

(1) Clearance from Windows. Final spans to the building they supply, or from which they are fed, shall be permitted to be attached to the building, but they shall be kept not less than 900 mm (3 ft) from windows that are designed to be opened, and from doors, porches, balconies, ladders, stairs, fire escapes, or similar locations.

Exception: Conductors run above the top level of a window shall be permitted to be less than the 900-mm (3-ft) requirement.

(2) Vertical Clearance. The vertical clearance of final spans above, or within 900 mm (3 ft) measured horizontally of, platforms, projections, or surfaces from which they might be reached shall be maintained in accordance with 225.18.

(3) Building Openings. The overhead branch-circuit and feeder conductors shall not be installed beneath openings through which materials may be moved, such as openings in farm and commercial buildings, and shall not be installed where they obstruct entrance to these buildings’ openings.

(E) Zone for Fire Ladders. Where buildings exceed three stories or 15 m (50 ft) in height, overhead lines shall be arranged, where practicable, so that a clear space (or zone) at least 1.8 m (6 ft) wide will be left either adjacent to the buildings or beginning not over 2.5 m (8 ft) from them to facilitate the raising of ladders when necessary for fire fighting.

225.20 Mechanical Protection of Conductors. Mechanical protection of conductors on buildings, structures, or poles shall be as provided for services in 230.50.

225.21 Multiconductor Cables on Exterior Surfaces of Buildings. Supports for multiconductor cables on exterior surfaces of buildings shall be as provided in 230.51.

225.22 Raceways on Exterior Surfaces of Buildings or Other Structures. Raceways on exteriors of buildings or other structures shall be arranged to drain and shall be suitable for use in wet locations.

225.24 Outdoor Lampholders. Where outdoor lampholders are attached as pendants, the connections to the circuit wires shall be staggered. Where such lampholders have terminals of a type that puncture the insulation and make contact with the conductors, they shall be attached only to conductors of the stranded type.

225.25 Location of Outdoor Lamps. Locations of lamps for outdoor lighting shall be below all energized conductors, transformers, or other electric utilization equipment, unless either of the following apply:

  1. Clearances or other safeguards are provided for relamping operations.
  2. Equipment is controlled by a disconnecting means that can be locked in the open position.

225.26 Vegetation as Support. Vegetation such as trees shall not be used for support of overhead conductor spans.

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225.27 Raceway Seal. Where a raceway enters a building or structure from an underground distribution system, it shall be sealed in accordance with 300.5(G). Spare or unused raceways shall also be sealed. Sealants shall be identified for use with the cable insulation, shield, or other components.

II. Buildings or Other Structures Supplied by a Feeder(s) or Branch Circuit(s)

225.30 Number of Supplies. A building or other structure that is served by a branch circuit or feeder on the load side of a service disconnecting means shall be supplied by only one feeder or branch circuit unless permitted in 225.30(A) through (E). For the purpose of this section, a multiwire branch circuit shall be considered a single circuit.

Where a branch circuit or feeder originates in these additional buildings or other structures, only one feeder or branch circuit shall be permitted to supply power back to the original building or structure, unless permitted in 225.30(A) through (E).

For the purpose of this section, a multiwire branch circuit shall be considered a single circuit.

(A) Special Conditions. Additional feeders or branch circuits shall be permitted to supply the following:

  1. Fire pumps
  2. Emergency systems
  3. Legally required standby systems
  4. Optional standby systems
  5. Parallel power production systems
  6. Systems designed for connection to multiple sources of supply for the purpose of enhanced reliability

(B) Special Occupancies. By special permission, additional feeders or branch circuits shall be permitted for either of the following:

  1. Multiple-occupancy buildings where there is no space available for supply equipment accessible to all occupants
  2. A single building or other structure sufficiently large to make two or more supplies necessary

(C) Capacity Requirements. Additional feeders or branch circuits shall be permitted where the capacity requirements are in excess of 2000 amperes at a supply voltage of 600 volts or less.

(D) Different Characteristics. Additional feeders or branch circuits shall be permitted for different voltages, frequencies, or phases or for different uses, such as control of outside lighting from multiple locations.

(E) Documented Switching Procedures. Additional feeders or branch circuits shall be permitted to supply installations under single management where documented safe switching procedures are established and maintained for disconnection.

225.31 Disconnecting Means. Means shall be provided for disconnecting all ungrounded conductors that supply or pass through the building or structure.

225.32 Location. The disconnecting means shall be installed either inside or outside of the building or structure served or where the conductors pass through the building or structure. The disconnecting means shall be at a readily accessible location nearest the point of entrance of the conductors. For the purposes of this section, the requirements in 230.6 shall be utilized.

Exception No. 1: For installations under single management, where documented safe switching procedures are established and maintained for disconnection, and where the installation is monitored by qualified individuals, the disconnecting means shall be permitted to be located elsewhere on the premises.

Exception No. 2: For buildings or other structures qualifying under the provisions of Article 685, the disconnecting means shall be permitted to be located elsewhere on the premises.

Exception No. 3: For towers or poles used as lighting standards, the disconnecting means shall be permitted to be located elsewhere on the premises.

Exception No. 4: For poles or similar structures used only for support of signs installed in accordance with Article 600, the disconnecting means shall be permitted to be located elsewhere on the premises.

225.33 Maximum Number of Disconnects.

(A) General. The disconnecting means for each supply permitted by 225.30 shall consist of not more than six switches or six circuit breakers mounted in a single enclosure, in a group of separate enclosures, or in or on a switchboard. There shall be no more than six disconnects per supply grouped in any one location.

Exception: For the purposes of this section, disconnecting means used solely for the control circuit of the ground-fault protection system, or the control circuit of the power-operated supply disconnecting means, installed as part of the listed equipment, shall not be considered a supply disconnecting means.

(B) Single-Pole Units. Two or three single-pole switches or breakers capable of individual operation shall be permitted on multiwire circuits, one pole for each ungrounded conductor, as one multipole disconnect, provided they are equipped with identified handle ties or a master handle to

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disconnect all ungrounded conductors with no more than six operations of the hand.

225.34 Grouping of Disconnects.

(A) General. The two to six disconnects as permitted in 225.33 shall be grouped. Each disconnect shall be marked to indicate the load served.

Exception: One of the two to six disconnecting means permitted in 225.33, where used only for a water pump also intended to provide fire protection, shall be permitted to be located remote from the other disconnecting means.

(B) Additional Disconnecting Means. The one or more additional disconnecting means for fire pumps or for emergency, legally required standby or optional standby system permitted by 225.30 shall be installed sufficiently remote from the one to six disconnecting means for normal supply to minimize the possibility of simultaneous interruption of supply.

225.35 Access to Occupants. In a multiple-occupancy building, each occupant shall have access to the occupant’s supply disconnecting means.

Exception: In a multiple-occupancy building where electric supply and electrical maintenance are provided by the building management and where these are under continuous building management supervision, the supply disconnecting means supplying more than one occupancy shall be permitted to be accessible to authorized management personnel only.

225.36 Suitable for Service Equipment. The disconnecting means specified in 225.31 shall be suitable for use as service equipment.

Exception: For garages and outbuildings on residential property, a snap switch or a set of 3-way or 4-way snap switches shall be permitted as the disconnecting means.

225.37 Identification. Where a building or structure has any combination of feeders, branch circuits, or services passing through it or supplying it, a permanent plaque or directory shall be installed at each feeder and branch-circuit disconnect location denoting all other services, feeders, or branch circuits supplying that building or structure or passing through that building or structure and the area served by each.

Exception No. 1: A plaque or directory shall not be required for large-capacity multibuilding industrial installations under single management, where it is ensured that disconnection can be accomplished by establishing and maintaining safe switching procedures.

Exception No. 2: This identification shall not be required for branch circuits installed from a dwelling unit to a second building or structure.

225.38 Disconnect Construction. Disconnecting means shall meet the requirements of 225.38(A) through (D).

Exception: For garages and outbuildings on residential property, snap switches or 3-way or 4-way snap switches shall be permitted as the disconnecting means.

(A) Manually or Power Operable. The disconnecting means shall consist of either (1) a manually operable switch or a circuit breaker equipped with a handle or other suitable operating means or (2) a power-operable switch or circuit breaker, provided the switch or circuit breaker can be opened by hand in the event of a power failure.

(B) Simultaneous Opening of Poles. Each building or structure disconnecting means shall simultaneously disconnect all ungrounded supply conductors that it controls from the building or structure wiring system.

(C) Disconnection of Grounded Conductor. Where the building or structure disconnecting means does not disconnect the grounded conductor from the grounded conductors in the building or structure wiring, other means shall be provided for this purpose at the location of disconnecting means. A terminal or bus to which all grounded conductors can be attached by means of pressure connectors shall be permitted for this purpose.

In a multisection switchboard, disconnects for the grounded conductor shall be permitted to be in any section of the switchboard, provided any such switchboard section is marked.

(D) Indicating. The building or structure disconnecting means shall plainly indicate whether it is in the open or closed position.

225.39 Rating of Disconnect. The feeder or branch-circuit disconnecting means shall have a rating of not less than the calculated load to be supplied, determined in accordance with Parts I and II of Article 220 for branch circuits, Part III or IV of Article 220 for feeders, or Part V of Article 220 for farm loads. Where the branch circuit or feeder disconnecting means consists of more than one switch or circuit breaker, as permitted by 225.33, combining the ratings of all the switches or circuit breakers for determining the rating of the disconnecting means shall be permitted. In no case shall the rating be lower than specified in 225.39(A), (B), (C), or (D).

(A) One-Circuit Installation. For installations to supply only limited loads of a single branch circuit, the branch circuit disconnecting means shall have a rating of not less than 15 amperes.

(B) Two-Circuit Installations. For installations consisting of not more than two 2-wire branch circuits, the feeder or

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branch-circuit disconnecting means shall have a rating of not less than 30 amperes.

(C) One-Family Dwelling. For a one-family dwelling, the feeder disconnecting means shall have a rating of not less than 100 amperes, 3-wire.

(D) All Others. For all other installations, the feeder or branch-circuit disconnecting means shall have a rating of not less than 60 amperes.

225.40 Access to Overcurrent Protective Devices. Where a feeder overcurrent device is not readily accessible, branch-circuit overcurrent devices shall be installed on the load side, shall be mounted in a readily accessible location, and shall be of a lower ampere rating than the feeder overcurrent device.

III. Over 600 Volts

225.50 Sizing of Conductors. The sizing of conductors over 600 volts shall be in accordance with 210.19(B) for branch circuits and 215.2(B) for feeders.

225.51 Isolating Switches. Where oil switches or air, oil, vacuum, or sulfur hexafluoride circuit breakers constitute a building disconnecting means, an isolating switch with visible break contacts and meeting the requirements of 230.204(B), (C), and (D) shall be installed on the supply side of the disconnecting means and all associated equipment.

Exception: The isolating switch shall not be required where the disconnecting means is mounted on removable truck panels or metal-enclosed switchgear units that cannot be opened unless the circuit is disconnected and that, when removed from the normal operating position, automatically disconnect the circuit breaker or switch from all energized parts.

225.52 Disconnecting Means.

(A) Location. A building or structure disconnecting means shall be located in accordance with 225.32, or it shall be electrically operated by a similarly located remote-control device.

(B) Type. Each building or structure disconnect shall simultaneously disconnect all ungrounded supply conductors it controls and shall have a fault-closing rating not less than the maximum available short-circuit current available at its supply terminals.

Exception: Where the individual disconnecting means consists of fused cutouts, the simultaneous disconnection of all ungrounded supply conductors shall not be required if there is a means to disconnect the load before opening the cutouts. A permanent legible sign shall be installed adjacent to the fused cutouts indicating the above requirement.

Where fused switches or separately mounted fuses are installed, the fuse characteristics shall be permitted to contribute to the fault closing rating of the disconnecting means.

(C) Locking. Disconnecting means shall be capable of being locked in the open position. The provisions for locking shall remain in place with or without the lock installed.

Exception: Where an individual disconnecting means consists of fused cutouts, a suitable enclosure capable of being locked and sized to contain all cutout fuse holders shall be installed at a convenient location to the fused cutouts.

(D) Indicating. Disconnecting means shall clearly indicate whether they are in the open “off” or closed “on” position.

(E) Uniform Position. Where disconnecting means handles are operated vertically, the “up” position of the handle shall be the “on” position.

Exception: A switching device having more than one “on” position, such as a double throw switch, shall not be required to comply with this requirement.

(F) Identification. Where a building or structure has any combination of feeders, branch circuits, or services passing through or supplying it, a permanent plaque or directory shall be installed at each feeder and branch-circuit disconnect location that denotes all other services, feeders, or branch circuits supplying that building or structure or passing through that building or structure and the area served by each.

225.56 Inspections and Tests.

(A) Pre-Energization and Operating Tests. The complete electrical system shall be performance tested when first installed on-site. Each protective, switching, and control circuit shall be adjusted in accordance with the recommendations of the protective device study and tested by actual operation using current injection or equivalent methods as necessary to ensure that each and every such circuit operates correctly to the satisfaction of the authority having jurisdiction.

(1) Instrument Transformers. All instrument transformers shall be tested to verify correct polarity and burden.

(2) Protective Relays. Each protective relay shall be demonstrated to operate by injecting current or voltage, or both, at the associated instrument transformer output terminal and observing that the associated switching and signaling functions occur correctly and in proper time and sequence to accomplish the protective function intended.

(3) Switching Circuits. Each switching circuit shall be observed to operate the associated equipment being switched.

(4) Control and Signal Circuits. Each control or signal circuit shall be observed to perform its proper control function or produce a correct signal output.

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(5) Metering Circuits. All metering circuits shall be verified to operate correctly from voltage and current sources, similarly to protective relay circuits.

(6) Acceptance Tests. Complete acceptance tests shall be performed, after the station installation is completed, on all assemblies, equipment, conductors, and control and protective systems, as applicable, to verify the integrity of all the systems.

(7) Relays and Metering Utilizing Phase Differences. All relays and metering that use phase differences for operation shall be verified by measuring phase angles at the relay under actual load conditions after operation commences.

(B) Test Report. A test report covering the results of the tests required in 225.56(A) shall be delivered to the authority having jurisdiction prior to energization.

Informational Note: For acceptance specifications, see NETA ATS-2007, Acceptance Testing Specifications for Electrical Power Distribution Equipment and Systems, published by the InterNational Electrical Testing Association.

225.60 Clearances over Roadways, Walkways, Rail, Water, and Open Land.

(A) 22 kV, Nominal, to Ground or Less. The clearances over roadways, walkways, rail, water, and open land for conductors and live parts up to 22 kV, nominal, to ground or less shall be not less than the values shown in Table 225.60.

(B) Over 22 kV Nominal to Ground. Clearances for the categories shown in Table 225.60 shall be increased by 10 mm (0.4 in.) per kV above 22,000 volts.

(C) Special Cases. For special cases, such as where crossings will be made over lakes, rivers, or areas using large vehicles such as mining operations, specific designs shall be engineered considering the special circumstances and shall be approved by the authority having jurisdiction.

Informational Note: For additional information, see ANSI C2-2007, National Electrical Safety Code.

225.61 Clearances over Buildings and Other Structures.

(A) 22 kV Nominal to Ground or Less. The clearances over buildings and other structures for conductors and live parts up to 22 kV, nominal, to ground or less shall be not less than the values shown in Table 225.61.

(B) Over 22 kV Nominal to Ground. Clearances for the categories shown in Table 225.61 shall be increased by 10 mm (0.4 in.) per kV above 22,000 volts.

Informational Note: For additional information, see ANSI C2-2007, National Electrical Safety Code.

Table 225.60 Clearances over Roadways, Walkways, Rail, Water, and Open Land
  Clearance
Location m ft
Open land subject to vehicles, cultivation, or grazing 5.6 18.5
Roadways, driveways, parking lots, and alleys 5.6 18.5
Walkways 4.1 13.5
Rails 8.1 26.5
Spaces and ways for pedestrians and restricted traffic 4.4 14.5
Water areas not suitable for boating 5.2 17.0

 

Table 225.61 Clearances over Buildings and Other Structures
Clearance from Conductors or Live Parts from: Horizontal Vertical
m ft m ft
Building walls, projections, and windows 2.3 7.5
Balconies, catwalks, and similar areas accessible to people 2.3 7.5 4.1 13.5
Over or under roofs or projections not readily accessible to people 3.8 12.5
Over roofs accessible to vehicles but not trucks 4.1 13.5
Over roofs accessible to trucks 5.6 18.5
Other structures 2.3 7.5

225.70 Substations.

(A) Warning Signs.

(1) General. A permanent, legible warning notice carrying the wording “DANGER — HIGH VOLTAGE” shall be placed in a conspicuous position in the following areas:

(a) At all entrances to electrical equipment vaults and electrical equipment rooms, areas, or enclosures

(b) At points of access to conductors on all high-voltage conduit systems and cable systems

(c) On all cable trays containing high-voltage conductors with the maximum spacing of warning notices not to exceed 3 m (10 ft.)

(2) Isolating Equipment. Permanent legible signs shall be installed at isolating equipment warning against operation while carrying current, unless the equipment is interlocked so that it cannot be operated under load.

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(3) Fuse Locations. Suitable warning signs shall be erected in a conspicuous place adjacent to fuses, warning operators not to replace fuses while the circuit is energized.

(4) Backfeed. The following steps shall be taken where the possibility of backfeed exists:

(a) Each group-operated isolating switch or disconnecting means shall bear a warning notice to the effect that contacts on either side of the device might be energized.

(b) A permanent, legible, single-line diagram of the station switching arrangement, clearly identifying each point of connection to the high-voltage section, shall be provided in a conspicuous location within sight of each point of connection.

(5) Metal-Enclosed and Metal-Clad Switchgear. Where metal-enclosed switchgear is installed, the following steps shall be taken:

(a) A permanent, legible, single-line diagram of the switchgear shall be provided in a readily visible location within sight of the switchgear, and this diagram shall clearly identify interlocks, isolation means, and all possible sources of voltage to the installation under normal or emergency conditions, including all equipment contained in each cubicle, and the marking on the switchgear shall cross-reference the diagram.

Exception to (a):Where the equipment consists solely of a single cubicle or metal-enclosed unit substation containing only one set of high-voltage switching devices, diagrams shall not he required.

(b) Permanent, legible signs shall be installed on panels or doors that provide access to live parts over 600 volts and shall carry the wording “DANGER — HIGH VOLTAGE” to warn of the danger of opening while energized.

(c) Where the panel provides access to parts that can only be de-energized and visibly isolated by the serving utility, the warning shall include that access is limited to the serving utility or following an authorization of the serving utility.

ARTICLE 230
Services

230.1 Scope. This article covers service conductors and equipment for control and protection of services and their installation requirements.

Informational Note: See Figure 230.1.

Figure 230.1 Services.

Figure 230.1 Services.

I. General

230.2 Number of Services. A building or other structure served shall be supplied by only one service unless permitted in 230.2(A) through (D). For the purpose of 230.40, Exception No. 2 only, underground sets of conductors, 1/0 AWG and larger, running to the same location and connected together at their supply end but not connected together at their load end shall be considered to be supplying one service.

(A) Special Conditions. Additional services shall be permitted to supply the following:

  1. Fire pumps
  2. Emergency systems
  3. Legally required standby systems
  4. Optional standby systems
  5. Parallel power production systems
  6. Systems designed for connection to multiple sources of supply for the purpose of enhanced reliability
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(B) Special Occupancies. By special permission, additional services shall be permitted for either of the following:

  1. Multiple-occupancy buildings where there is no available space for service equipment accessible to all occupants
  2. A single building or other structure sufficiently large to make two or more services necessary

(C) Capacity Requirements. Additional services shall be permitted under any of the following:

  1. Where the capacity requirements are in excess of 2000 amperes at a supply voltage of 600 volts or less
  2. Where the load requirements of a single-phase installation are greater than the serving agency normally supplies through one service
  3. By special permission

(D) Different Characteristics. Additional services shall be permitted for different voltages, frequencies, or phases, or for different uses, such as for different rate schedules.

(E) Identification. Where a building or structure is supplied by more than one service, or any combination of branch circuits, feeders, and services, a permanent plaque or directory shall be installed at each service disconnect location denoting all other services, feeders, and branch circuits supplying that building or structure and the area served by each. See 225.37.

230.3 One Building or Other Structure Not to Be Supplied Through Another. Service conductors supplying a building or other structure shall not pass through the interior of another building or other structure.

230.6 Conductors Considered Outside the Building. Conductors shall be considered outside of a building or other structure under any of the following conditions:

  1. Where installed under not less than 50 mm (2 in.) of concrete beneath a building or other structure
  2. Where installed within a building or other structure in a raceway that is encased in concrete or brick not less than 50 mm (2 in.) thick
  3. Where installed in any vault that meets the construction requirements of Article 450, Part III
  4. Where installed in conduit and under not less than 450 mm (18 in.) of earth beneath a building or other structure
  5. Where installed in overhead service masts on the outside surface of the building traveling through the eave of that building to meet the requirements of 230.24

230.7 Other Conductors in Raceway or Cable. Conductors other than service conductors shall not be installed in the same service raceway or service cable.

Exception No. 1: Grounding conductors and bonding jumpers.

Exception No. 2: Load management control conductors having overcurrent protection.

230.8 Raceway Seal. Where a service raceway enters a building or structure from an underground distribution system, it shall be sealed in accordance with 300.5(G). Spare or unused raceways shall also be sealed. Sealants shall be identified for use with the cable insulation, shield, or other components.

230.9 Clearances on Buildings. Service conductors and final spans shall comply with 230.9(A), (B), and (C).

(A) Clearances. Service conductors installed as open conductors or multiconductor cable without an overall outer jacket shall have a clearance of not less than 900 mm (3 ft) from windows that are designed to be opened, doors, porches, balconies, ladders, stairs, fire escapes, or similar locations.

Exception: Conductors run above the top level of a window shall be permitted to be less than the 900-mm (3-ft) requirement.

(B) Vertical Clearance. The vertical clearance of final spans above, or within 900 mm (3 ft) measured horizontally of, platforms, projections, or surfaces from which they might be reached shall be maintained in accordance with 230.24(B).

(C) Building Openings. Overhead service conductors shall not be installed beneath openings through which materials may be moved, such as openings in farm and commercial buildings, and shall not be installed where they obstruct entrance to these building openings.

230.10 Vegetation as Support. Vegetation such as trees shall not be used for support of overhead service conductors.

II. Overhead Service Conductors

230.22 Insulation or Covering. Individual conductors shall be insulated or covered.

Exception: The grounded conductor of a multiconductor cable shall be permitted to be bare.

230.23 Size and Rating.

(A) General. Conductors shall have sufficient ampacity to carry the current for the load as calculated in accordance with Article 220 and shall have adequate mechanical strength.

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(B) Minimum Size. The conductors shall not be smaller than 8 AWG copper or 6 AWG aluminum or copper-clad aluminum.

Exception: Conductors supplying only limited loads of a single branch circuit — such as small polyphase power, controlled water heaters, and similar loads — shall not be smaller than 12 AWG hard-drawn copper or equivalent.

(C) Grounded Conductors. The grounded conductor shall not be less than the minimum size as required by 250.24(C).

230.24 Clearances. Overhead service conductors shall not be readily accessible and shall comply with 230.24(A) through (E) for services not over 600 volts, nominal.

(A) Above Roofs. Conductors shall have a vertical clearance of not less than 2.5 m (8 ft) above the roof surface. The vertical clearance above the roof level shall be maintained for a distance of not less than 900 mm (3 ft) in all directions from the edge of the roof.

Exception No. 1: The area above a roof surface subject to pedestrian or vehicular traffic shall have a vertical clearance from the roof surface in accordance with the clearance requirements of 230.24(B).

Exception No. 2: Where the voltage between conductors does not exceed 300 and the roof has a slope of 100 mm in 300 mm (4 in. in 12 in.) or greater, a reduction in clearance to 900 mm (3 ft) shall be permitted.

Exception No. 3: Where the voltage between conductors does not exceed 300, a reduction in clearance above only the overhanging portion of the roof to not less than 450 mm (18 in.) shall be permitted if (1) not more than 1.8 m (6 ft) of overhead service conductors, 1.2 m (4 ft) horizontally, pass above the roof overhang, and (2) they are terminated at a through-the-roof raceway or approved support.

Informational Note: See 230.28 for mast supports.

Exception No. 4: The requirement for maintaining the vertical clearance 900 mm (3 ft) from the edge of the roof shall not apply to the final conductor span where the service drop is attached to the side of a building.

Exception No. 5: Where the voltage between conductors does not exceed 300 and the roof area is guarded or isolated, a reduction in clearance to 900 mm (3 ft) shall be permitted.

(B) Vertical Clearance for Overhead Service Conductors. Overhead service conductors, where not in excess of 600 volts, nominal, shall have the following minimum clearance from final grade:

  1. 3.0 m (10 ft) — at the electrical service entrance to buildings, also at the lowest point of the drip loop of the building electrical entrance, and above areas or sidewalks accessible only to pedestrians, measured from final grade or other accessible surface only for service-drop cables supported on and cabled together with a grounded bare messenger where the voltage does not exceed 150 volts to ground
  2. 3.7 m (12 ft) — over residential property and driveways, and those commercial areas not subject to truck traffic where the voltage does not exceed 300 volts to ground
  3. 4.5 m (15 ft) — for those areas listed in the 3.7-m (12-ft) classification where the voltage exceeds 300 volts to ground
  4. 5.5 m (18 ft) — over public streets, alleys, roads, parking areas subject to truck traffic, driveways on other than residential property, and other land such as cultivated, grazing, forest, and orchard

(C) Clearance from Building Openings. See 230.9.

(D) Clearance from Swimming Pools. See 680.8.

(E) Clearance from Communication Wires and Cables. Clearance from communication wires and cables shall be in accordance with 800.44(A)(4).

230.26 Point of Attachment. The point of attachment of the service-drop conductors to a building or other structure shall provide the minimum clearances as specified in 230.9 and 230.24. In no case shall this point of attachment be less than 3.0 m (10 ft) above finished grade.

230.27 Means of Attachment. Multiconductor cables used for overhead service conductors shall be attached to buildings or other structures by fittings identified for use with service conductors. Open conductors shall be attached to fittings identified for use with service conductors or to non-combustible, nonabsorbent insulators securely attached to the building or other structure.

230.28 Service Masts as Supports. Where a service mast is used for the support of service-drop conductors, it shall be of adequate strength or be supported by braces or guys to withstand safely the strain imposed by the service drop. Where raceway-type service masts are used, all raceway fittings shall be identified for use with service masts. Only power service-drop conductors shall be permitted to be attached to a service mast.

230.29 Supports over Buildings. Service conductors passing over a roof shall be securely supported by substantial structures. Where practicable, such supports shall be independent of the building.

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III. Underground Service Conductors

230.30 Insulation. Service-lateral conductors shall be insulated for the applied voltage.

Exception: A grounded conductor shall be permitted to be uninsulated as follows:

  1. Bare copper used in a raceway.
  2. Bare copper for direct burial where bare copper is judged to be suitable for the soil conditions.
  3. Bare copper for direct burial without regard to soil conditions where part of a cable assembly identified for underground use.
  4. Aluminum or copper-clad aluminum without individual insulation or covering where part of a cable assembly identified for underground use in a raceway or for direct burial.

230.31 Size and Rating.

(A) General. Underground service conductors shall have sufficient ampacity to carry the current for the load as calculated in accordance with Article 220 and shall have adequate mechanical strength.

(B) Minimum Size. The conductors shall not be smaller than 8 AWG copper or 6 AWG aluminum or copper-clad aluminum.

Exception: Conductors supplying only limited loads of a single branch circuit — such as small polyphase power, controlled water heaters, and similar loads — shall not be smaller than 12 AWG copper or 10 AWG aluminum or copper-clad aluminum.

(C) Grounded Conductors. The grounded conductor shall not be less than the minimum size required by 250.24(C).

230.32 Protection Against Damage. Underground service conductors shall be protected against damage in accordance with 300.5. Service conductors entering a building or other structure shall be installed in accordance with 230.6 or protected by a raceway wiring method identified in 230.43.

230.33 Spliced Conductors. Service conductors shall be permitted to be spliced or tapped in accordance with 110.14, 300.5(E), 300.13, and 300.15.

IV. Service-Entrance Conductors

230.40 Number of Service-Entrance Conductor Sets. Each service drop, set of overhead service conductors, set of underground service conductors, or service lateral shall supply only one set of service-entrance conductors.

Exception No. 1: A building with more than one occupancy shall be permitted to have one set of service-entrance conductors for each service, as defined in 230.2, run to each occupancy or group of occupancies. If the number of service disconnect locations for any given classification of service does not exceed six, the requirements of 230.2(E) shall apply at each location. If the number of service disconnect locations exceeds six for any given supply classification, all service disconnect locations for all supply characteristics, together with any branch circuit or feeder supply sources, if applicable, shall be clearly described using suitable graphics or text, or both, on one or more plaques located in an approved, readily accessible location(s) on the building or structure served and as near as practicable to the point(s) of attachment or entry(ies) for each service drop or service lateral, and for each set of overhead or underground service conductors.

Exception No. 2: Where two to six service disconnecting means in separate enclosures are grouped at one location and supply separate loads from one service drop, set of overhead service conductors, set of underground service conductors, or service lateral, one set of service-entrance conductors shall be permitted to supply each or several such service equipment enclosures.

Exception No. 3: A single-family dwelling unit and its accessory structures shall be permitted to have one set of service-entrance conductors run to each from a single service drop, set of overhead service conductors, set of underground service conductors, or service lateral.

Exception No. 4: Two-family dwellings, multifamily dwellings, and multiple occupancy buildings shall be permitted to have one set of service-entrance conductors installed to supply the circuits covered in 210.25.

Exception No. 5: One set of service-entrance conductors connected to the supply side of the normal service disconnecting means shall be permitted to supply each or several systems covered by 230.82(5) or 230.82(6).

230.41 Insulation of Service-Entrance Conductors. Service-entrance conductors entering or on the exterior of buildings or other structures shall be insulated.

Exception: A grounded conductor shall be permitted to be uninsulated as follows:

  1. Bare copper used in a raceway or part of a service cable assembly.
  2. Bare copper for direct burial where bare copper is judged to be suitable for the soil conditions.
  3. Bare copper for direct burial without regard to soil conditions where part of a cable assembly identified for underground use.70-81
  4. Aluminum or copper-clad aluminum without individual insulation or covering where part of a cable assembly or identified for underground use in a raceway, or for direct burial.
  5. Bare conductors used in an auxiliary gutter.

230.42 Minimum Size and Rating.

(A) General. The ampacity of the service-entrance conductors before the application of any adjustment or correction factors shall not be less than either 230.42(A)(1) or (A)(2). Loads shall be determined in accordance with Part III, IV, or V of Article 220, as applicable. Ampacity shall be determined from 310.15. The maximum allowable current of busways shall be that value for which the busway has been listed or labeled.

  1. The sum of the noncontinuous loads plus 125 percent of continuous loads

    Exception: Grounded conductors that are not connected to an overcurrent device shall be permitted to be sized at 100 percent of the continuous and noncontinuous load.

  2. The sum of the noncontinuous load plus the continuous load if the service-entrance conductors terminate in an overcurrent device where both the overcurrent device and its assembly are listed for operation at 100 percent of their rating

(B) Specific Installations. In addition to the requirements of 230.42(A), the minimum ampacity for ungrounded conductors for specific installations shall not be less than the rating of the service disconnecting means specified in 230.79(A) through (D).

(C) Grounded Conductors. The grounded conductor shall not be smaller than the minimum size as required by 250.24(C).

230.43 Wiring Methods for 600 Volts, Nominal, or Less. Service-entrance conductors shall be installed in accordance with the applicable requirements of this Code covering the type of wiring method used and shall be limited to the following methods:

  1. Open wiring on insulators
  2. Type IGS cable
  3. Rigid metal conduit
  4. Intermediate metal conduit
  5. Electrical metallic tubing
  6. Electrical nonmetallic tubing (ENT)
  7. Service-entrance cables
  8. Wireways
  9. Busways
  10. Auxiliary gutters
  11. Rigid polyvinyl chloride conduit (PVC)
  12. Cablebus
  13. Type MC cable
  14. Mineral-insulated, metal-sheathed cable
  15. Flexible metal conduit not over 1.8 m (6 ft) long or liquidtight flexible metal conduit not over 1.8 m (6 ft) long between raceways, or between raceway and service equipment, with equipment bonding jumper routed with the flexible metal conduit or the liquidtight flexible metal conduit according to the provisions of 250.102(A), (B), (C), and (E)
  16. Liquidtight flexible nonmetallic conduit
  17. High density polyethylene conduit (HDPE)
  18. Nonmetallic underground conduit with conductors (NUCC)
  19. Reinforced thermosetting resin conduit (RTRC)

230.44 Cable Trays. Cable tray systems shall be permitted to support service-entrance conductors. Cable trays used to support service-entrance conductors shall contain only service-entrance conductors and shall be limited to the following methods:

  1. Type SE cable
  2. Type MC cable
  3. Type MI cable
  4. Type IGS cable
  5. Single thermoplastic-insulated conductors 1/0 and larger with CT rating

Such cable trays shall be identified with permanently affixed labels with the wording “Service-Entrance Conductors.” The labels shall be located so as to be visible after installation and placed so that the service-entrance conductors are able to be readily traced through the entire length of the cable tray.

Exception: Conductors, other than service-entrance conductors, shall be permitted to be installed in a cable tray with service-entrance conductors, provided a solid fixed barrier of a material compatible with the cable tray is installed to separate the service-entrance conductors from other conductors installed in the cable tray.

230.46 Spliced Conductors. Service-entrance conductors shall be permitted to be spliced or tapped in accordance with 110.14, 300.5(E), 300.13, and 300.15.

230.50 Protection Against Physical Damage.

(A) Underground Service-Entrance Conductors. Underground service-entrance conductors shall be protected against physical damage in accordance with 300.5.

(B) All Other Service-Entrance Conductors. All other service-entrance conductors, other than underground service

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entrance conductors, shall be protected against physical damage as specified in 230.50(B)(1) or (B)(2).

(1) Service-Entrance Cables. Service-entrance cables, where subject to physical damage, shall be protected by any of the following:

  1. Rigid metal conduit
  2. Intermediate metal conduit
  3. Schedule 80 PVC conduit
  4. Electrical metallic tubing
  5. Reinforced thermosetting resin conduit (RTRC)
  6. Other approved means

(2) Other Than Service-Entrance Cables. Individual open conductors and cables, other than service-entrance cables, shall not be installed within 3.0 m (10 ft) of grade level or where exposed to physical damage.

Exception: Type MI and Type MC cable shall be permitted within 3.0 m (10 ft) of grade level where not exposed to physical damage or where protected in accordance with 300.5(D).

230.51 Mounting Supports. Service-entrance cables or individual open service-entrance conductors shall be supported as specified in 230.51(A), (B), or (C).

(A) Service-Entrance Cables. Service-entrance cables shall be supported by straps or other approved means within 300 mm (12 in.) of every service head, gooseneck, or connection to a raceway or enclosure and at intervals not exceeding 750 mm (30 in.).

(B) Other Cables. Cables that are not approved for mounting in contact with a building or other structure shall be mounted on insulating supports installed at intervals not exceeding 4.5 m (15 ft) and in a manner that maintains a clearance of not less than 50 mm (2 in.) from the surface over which they pass.

(C) Individual Open Conductors. Individual open conductors shall be installed in accordance with Table 230.51(C). Where exposed to the weather, the conductors shall be mounted on insulators or on insulating supports attached to racks, brackets, or other approved means. Where not exposed to the weather, the conductors shall be mounted on glass or porcelain knobs.

230.52 Individual Conductors Entering Buildings or Other Structures. Where individual open conductors enter a building or other structure, they shall enter through roof bushings or through the wall in an upward slant through individual, noncombustible, nonabsorbent insulating tubes. Drip loops shall be formed on the conductors before they enter the tubes.

230.53 Raceways to Drain. Where exposed to the weather, raceways enclosing service-entrance conductors shall be suitable for use in wet locations and arranged to drain. Where embedded in masonry, raceways shall be arranged to drain.

230.54 Overhead Service Locations.

(A) Service Head. Service raceways shall be equipped with a service head at the point of connection to service-drop or overhead service conductors. The service head shall be listed for use in wet locations.

(B) Service-Entrance Cables Equipped with Service Head or Gooseneck. Service-entrance cables shall be equipped with a service head. The service head shall be listed for use in wet locations.

Exception: Type SE cable shall be permitted to be formed in a gooseneck and taped with a self-sealing weather-resistant thermoplastic.

(C) Service Heads and Goosenecks Above Service-Drop or Overhead Service Attachment. Service heads and goosenecks in service-entrance cables shall be located above the point of attachment of the service-drop or overhead service conductors to the building or other structure.

Exception: Where it is impracticable to locate the service head or gooseneck above the point of attachment, the service head or gooseneck location shall be permitted not farther than 600 mm (24 in.) from the point of attachment.

Table 230.51(C) Supports
Maximum Volts Maximum Distance Between Supports Minimum Clearance
Between Conductors From Surface
m ft mm in. mm in.
600 2.7 9 150 6 50 2
600 4.5 15 300 12 50 2
300 1.4 75 3 50 2
600* 1.4* 4½* 65* 2½* 25* 1*
*Where not exposed to weather.
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(D) Secured. Service-entrance cables shall be held securely in place.

(E) Separately Bushed Openings. Service heads shall have conductors of different potential brought out through separately bushed openings.

Exception: For jacketed multiconductor service-entrance cable without splice.

(F) Drip Loops. Drip loops shall be formed on individual conductors. To prevent the entrance of moisture, service-entrance conductors shall be connected to the service-drop or overhead service conductors either (1) below the level of the service head or (2) below the level of the termination of the service-entrance cable sheath.

(G) Arranged That Water Will Not Enter Service Raceway or Equipment. Service-entrance and overhead service conductors shall be arranged so that water will not enter service raceway or equipment.

230.56 Service Conductor with the Higher Voltage to Ground. On a 4-wire, delta-connected service where the midpoint of one phase winding is grounded, the service conductor having the higher phase voltage to ground shall be durably and permanently marked by an outer finish that is orange in color, or by other effective means, at each termination or junction point.

V. Service Equipment — General

230.62 Service Equipment — Enclosed or Guarded. Energized parts of service equipment shall be enclosed as specified in 230.62(A) or guarded as specified in 230.62(B).

(A) Enclosed. Energized parts shall be enclosed so that they will not be exposed to accidental contact or shall be guarded as in 230.62(B).

(B) Guarded. Energized parts that are not enclosed shall be installed on a switchboard, panelboard, or control board and guarded in accordance with 110.18 and 110.27. Where energized parts are guarded as provided in 110.27(A)(1) and (A)(2), a means for locking or sealing doors providing access to energized parts shall be provided.

230.66 Marking. Service equipment rated at 600 volts or less shall be marked to identify it as being suitable for use as service equipment. All service equipment shall be listed. Individual meter socket enclosures shall not be considered service equipment.

VI. Service Equipment — Disconnecting Means

230.70 General. Means shall be provided to disconnect all conductors in a building or other structure from the service-entrance conductors.

(A) Location. The service disconnecting means shall be installed in accordance with 230.70(A)(1), (A)(2), and (A)(3).

(1) Readily Accessible Location. The service disconnecting means shall be installed at a readily accessible location either outside of a building or structure or inside nearest the point of entrance of the service conductors.

(2) Bathrooms. Service disconnecting means shall not be installed in bathrooms.

(3) Remote Control. Where a remote control device(s) is used to actuate the service disconnecting means, the service disconnecting means shall be located in accordance with 230.70(A)(1).

(B) Marking. Each service disconnect shall be permanently marked to identify it as a service disconnect.

(C) Suitable for Use. Each service disconnecting means shall be suitable for the prevailing conditions. Service equipment installed in hazardous (classified) locations shall comply with the requirements of Articles 500 through 517.

230.71 Maximum Number of Disconnects.

(A) General. The service disconnecting means for each service permitted by 230.2, or for each set of service-entrance conductors permitted by 230.40, Exception No. 1, 3, 4, or 5, shall consist of not more than six switches or sets of circuit breakers, or a combination of not more than six switches and sets of circuit breakers, mounted in a single enclosure, in a group of separate enclosures, or in or on a switchboard. There shall be not more than six sets of disconnects per service grouped in any one location.

For the purpose of this section, disconnecting means installed as part of listed equipment and used solely for the following shall not be considered a service disconnecting means:

  1. Power monitoring equipment
  2. Surge-protective device(s)
  3. Control circuit of the ground-fault protection system
  4. Power-operable service disconnecting means

(B) Single-Pole Units. Two or three single-pole switches or breakers, capable of individual operation, shall be permitted on multiwire circuits, one pole for each ungrounded conductor, as one multipole disconnect, provided they are equipped with identified handle ties or a master handle to disconnect all conductors of the service with no more than six operations of the hand.

Informational Note: See 408.36, Exception No. 1 and Exception No. 3, for service equipment in certain panelboards, and see 430.95 for service equipment in motor control centers.

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230.72 Grouping of Disconnects.

(A) General. The two to six disconnects as permitted in 230.71 shall be grouped. Each disconnect shall be marked to indicate the load served.

Exception: One of the two to six service disconnecting means permitted in 230.71, where used only for a water pump also intended to provide fire protection, shall be permitted to be located remote from the other disconnecting means. If remotely installed in accordance with this exception, a plaque shall be posted at the location of the remaining grouped disconnects denoting its location.

(B) Additional Service Disconnecting Means. The one or more additional service disconnecting means for fire pumps, emergency systems, legally required standby, or optional standby services permitted by 230.2 shall be installed remote from the one to six service disconnecting means for normal service to minimize the possibility of simultaneous interruption of supply.

(C) Access to Occupants. In a multiple-occupancy building, each occupant shall have access to the occupant’s service disconnecting means.

Exception: In a multiple-occupancy building where electric service and electrical maintenance are provided by the building management and where these are under continuous building management supervision, the service disconnecting means supplying more than one occupancy shall be permitted to be accessible to authorized management personnel only.

230.74 Simultaneous Opening of Poles. Each service disconnect shall simultaneously disconnect all ungrounded service conductors that it controls from the premises wiring system.

230.75 Disconnection of Grounded Conductor. Where the service disconnecting means does not disconnect the grounded conductor from the premises wiring, other means shall be provided for this purpose in the service equipment. A terminal or bus to which all grounded conductors can be attached by means of pressure connectors shall be permitted for this purpose. In a multisection switchboard, disconnects for the grounded conductor shall be permitted to be in any section of the switchboard, provided any such switchboard section is marked.

230.76 Manually or Power Operable. The service disconnecting means for ungrounded service conductors shall consist of one of the following:

  1. A manually operable switch or circuit breaker equipped with a handle or other suitable operating means
  2. A power-operated switch or circuit breaker, provided the switch or circuit breaker can be opened by hand in the event of a power supply failure

230.77 Indicating. The service disconnecting means shall plainly indicate whether it is in the open (off) or closed (on) position.

230.79 Rating of Service Disconnecting Means. The service disconnecting means shall have a rating not less than the calculated load to be carried, determined in accordance with Part III, IV, or V of Article 220, as applicable. In no case shall the rating be lower than specified in 230.79(A), (B), (C), or (D).

(A) One-Circuit Installations. For installations to supply only limited loads of a single branch circuit, the service disconnecting means shall have a rating of not less than 15 amperes.

(B) Two-Circuit Installations. For installations consisting of not more than two 2-wire branch circuits, the service disconnecting means shall have a rating of not less than 30 amperes.

(C) One-Family Dwellings. For a one-family dwelling, the service disconnecting means shall have a rating of not less than 100 amperes, 3-wire.

(D) All Others. For all other installations, the service disconnecting means shall have a rating of not less than 60 amperes.

230.80 Combined Rating of Disconnects. Where the service disconnecting means consists of more than one switch or circuit breaker, as permitted by 230.71, the combined ratings of all the switches or circuit breakers used shall not be less than the rating required by 230.79.

230.81 Connection to Terminals. The service conductors shall be connected to the service disconnecting means by pressure connectors, clamps, or other approved means. Connections that depend on solder shall not be used.

230.82 Equipment Connected to the Supply Side of Service Disconnect. Only the following equipment shall be permitted to be connected to the supply side of the service disconnecting means:

  1. Cable limiters or other current-limiting devices.
  2. Meters and meter sockets nominally rated not in excess of 600 volts, provided all metal housings and service enclosures are grounded in accordance with Part VII and bonded in accordance with Part V of Article 250.
  3. Meter disconnect switches nominally rated not in excess of 600 volts that have a short-circuit current rating70-85 equal to or greater than the available short-circuit current, provided all metal housings and service enclosures are grounded in accordance with Part VII and bonded in accordance with Part V of Article 250. A meter disconnect switch shall be capable of interrupting the load served.
  4. Instrument transformers (current and voltage), impedance shunts, load management devices, surge arresters, and Type 1 surge-protective devices.
  5. Taps used only to supply load management devices, circuits for standby power systems, fire pump equipment, and fire and sprinkler alarms, if provided with service equipment and installed in accordance with requirements for service-entrance conductors.
  6. Solar photovoltaic systems, fuel cell systems, or interconnected electric power production sources.
  7. Control circuits for power-operable service disconnecting means, if suitable overcurrent protection and disconnecting means are provided.
  8. Ground-fault protection systems or Type 2 surge-protective devices, where installed as part of listed equipment, if suitable overcurrent protection and disconnecting means are provided.
  9. Connections used only to supply listed communications equipment under the exclusive control of the serving electric utility, if suitable overcurrent protection and disconnecting means are provided. For installations of equipment by the serving electric utility, a disconnecting means is not required if the supply is installed as part of a meter socket, such that access can only be gained with the meter removed.

VII. Service Equipment — Overcurrent Protection

230.90 Where Required. Each ungrounded service conductor shall have overload protection.

(A) Ungrounded Conductor. Such protection shall be provided by an overcurrent device in series with each ungrounded service conductor that has a rating or setting not higher than the allowable ampacity of the conductor. A set of fuses shall be considered all the fuses required to protect all the ungrounded conductors of a circuit. Single-pole circuit breakers, grouped in accordance with 230.71(B), shall be considered as one protective device.

Exception No. 1: For motor-starting currents, ratings that comply with 430.52, 430.62, and 430.63 shall be permitted.

Exception No. 2: Fuses and circuit breakers with a rating or setting that complies with 240.4(B) or (C) and 240.6 shall be permitted.

Exception No. 3: Two to six circuit breakers or sets of fuses shall be permitted as the overcurrent device to provide the overload protection. The sum of the ratings of the circuit breakers or fuses shall be permitted to exceed the ampacity of the service conductors, provided the calculated load does not exceed the ampacity of the service conductors.

Exception No. 4: Overload protection for fire pump supply conductors shall comply with 695.4(B)(2)(a).

Exception No. 5: Overload protection for 120/240-volt, 3-wire, single-phase dwelling services shall be permitted in accordance with the requirements of 310.]5(B)(6).

(B) Not in Grounded Conductor. No overcurrent device shall be inserted in a grounded service conductor except a circuit breaker that simultaneously opens all conductors of the circuit.

230.91 Location. The service overcurrent device shall be an integral part of the service disconnecting means or shall be located immediately adjacent thereto.

230.92 Locked Service Overcurrent Devices. Where the service overcurrent devices are locked or sealed or are not readily accessible to the occupant, branch-circuit or feeder overcurrent devices shall be installed on the load side, shall be mounted in a readily accessible location, and shall be of lower ampere rating than the service overcurrent device.

230.93 Protection of Specific Circuits. Where necessary to prevent tampering, an automatic overcurrent device that protects service conductors supplying only a specific load, such as a water heater, shall be permitted to be locked or sealed where located so as to be accessible.

230.94 Relative Location of Overcurrent Device and Other Service Equipment. The overcurrent device shall protect all circuits and devices.

Exception No. 1: The service switch shall be permitted on the supply side.

Exception No. 2: High-impedance shunt circuits, surge arresters, Type 1 surge-protective devices, surge-protective capacitors, and instrument transformers (current and voltage) shall be permitted to be connected and installed on the supply side of the service disconnecting means as permitted by 230.82.

Exception No. 3: Circuits for load management devices shall be permitted to be connected on the supply side of the service overcurrent device where separately provided with overcurrent protection.

Exception No. 4: Circuits used only for the operation of fire alarm, other protective signaling systems, or the supply to fire pump equipment shall be permitted to be connected on the supply side of the service overcurrent device where separately provided with overcurrent protection.

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Exception No. 5: Meters nominally rated not in excess of 600 volts shall be permitted, provided all metal housings and service enclosures are grounded.

Exception No. 6: Where service equipment is power operable, the control circuit shall be permitted to be connected ahead of the service equipment if suitable overcurrent protection and disconnecting means are provided.

230.95 Ground-Fault Protection of Equipment. Ground-fault protection of equipment shall be provided for solidly grounded wye electric services of more than 150 volts to ground but not exceeding 600 volts phase-to-phase for each service disconnect rated 1000 amperes or more. The grounded conductor for the solidly grounded wye system shall be connected directly to ground through a grounding electrode system, as specified in 250.50, without inserting any resistor or impedance device.

The rating of the service disconnect shall be considered to be the rating of the largest fuse that can be installed or the highest continuous current trip setting for which the actual overcurrent device installed in a circuit breaker is rated or can be adjusted.

Exception: The ground-fault protection provisions of this section shall not apply to a service disconnect for a continuous industrial process where a nonorderly shutdown will introduce additional or increased hazards.

(A) Setting. The ground-fault protection system shall operate to cause the service disconnect to open all ungrounded conductors of the faulted circuit. The maximum setting of the ground-fault protection shall be 1200 amperes, and the maximum time delay shall be one second for ground-fault currents equal to or greater than 3000 amperes.

(B) Fuses. If a switch and fuse combination is used, the fuses employed shall be capable of interrupting any current higher than the interrupting capacity of the switch during a time that the ground-fault protective system will not cause the switch to open.

(C) Performance Testing. The ground-fault protection system shall be performance tested when first installed on site. The test shall be conducted in accordance with instructions that shall be provided with the equipment. A written record of this test shall be made and shall be available to the authority having jurisdiction.

Informational Note No. 1: Ground-fault protection that functions to open the service disconnect affords no protection from faults on the line side of the protective element. It serves only to limit damage to conductors and equipment on the load side in the event of an arcing ground fault on the load side of the protective element.

Informational Note No. 2: This added protective equipment at the service equipment may make it necessary to review the overall wiring system for proper selective over-current protection coordination. Additional installations of ground-fault protective equipment may be needed on feeders and branch circuits where maximum continuity of electric service is necessary.

Informational Note No. 3: Where ground-fault protection is provided for the service disconnect and interconnection is made with another supply system by a transfer device, means or devices may be needed to ensure proper ground-fault sensing by the ground-fault protection equipment.

Informational Note No. 4: See 517.17(A) for information on where an additional step of ground-fault protection is required for hospitals and other buildings with critical areas or life support equipment.

VIII. Services Exceeding 600 Volts, Nominal

230.200 General. Service conductors and equipment used on circuits exceeding 600 volts, nominal, shall comply with all the applicable provisions of the preceding sections of this article and with the following sections that supplement or modify the preceding sections. In no case shall the provisions of Part VIII apply to equipment on the supply side of the service point.

Informational Note: For clearances of conductors of over 600 volts, nominal, see ANSI C2-2007, National Electrical Safety Code.

230.202 Service-Entrance Conductors. Service-entrance conductors to buildings or enclosures shall be installed to conform to 230.202(A) and (B).

(A) Conductor Size. Service-entrance conductors shall not be smaller than 6 AWG unless in multiconductor cable. Multiconductor cable shall not be smaller than 8 AWG.

(B) Wiring Methods. Service-entrance conductors shall be installed by one of the wiring methods covered in 300.37 and 300.50.

230.204 Isolating Switches.

(A) Where Required. Where oil switches or air, oil, vacuum, or sulfur hexafluoride circuit breakers constitute the service disconnecting means, an isolating switch with visible break contacts shall be installed on the supply side of the disconnecting means and all associated service equipment.

Exception: An isolating switch shall not he required where the circuit breaker or switch is mounted on removable truck panels or metal-enclosed switchgear units where both of the following conditions apply:

  1. Cannot be opened unless the circuit is disconnected,
  2. Where all energized parts are automatically disconnected when the circuit breaker or switch is removed from the normal operating position.
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(B) Fuses as Isolating Switch. Where fuses are of the type that can be operated as a disconnecting switch, a set of such fuses shall be permitted as the isolating switch.

(C) Accessible to Qualified Persons Only. The isolating switch shall be accessible to qualified persons only.

(D) Connection to Ground. Isolating switches shall be provided with a means for readily connecting the load side conductors to a grounding electrode system, equipment ground busbar, or grounded steel structure when disconnected from the source of supply.

A means for grounding the load side conductors to a grounding electrode system, equipment grounding busbar, or grounded structural steel shall not be required for any duplicate isolating switch installed and maintained by the electric supply company.

230.205 Disconnecting Means.

(A) Location. The service disconnecting means shall be located in accordance with 230.70.

For either overhead or underground primary distribution systems on private property, the service disconnect shall be permitted to be located in a location that is not readily accessible, if the disconnecting means can be operated by mechanical linkage from a readily accessible point, or electronically in accordance with 230.205(C), where applicable.

(B) Type. Each service disconnect shall simultaneously disconnect all ungrounded service conductors that it controls and shall have a fault-closing rating that is not less than the maximum short-circuit current available at its supply terminals.

Where fused switches or separately mounted fuses are installed, the fuse characteristics shall be permitted to contribute to the fault-closing rating of the disconnecting means.

(C) Remote Control, or multibuilding, industrial installations under single management, the service disconnecting means shall be permitted to be located at a separate building or structure. In such cases, the service disconnecting means shall be permitted to be electrically operated by a readily accessible, remote-control device.

230.206 Overcurrent Devices as Disconnecting Means. Where the circuit breaker or alternative for it, as specified in 230.208 for service overcurrent devices, meets the requirements specified in 230.205, they shall constitute the service disconnecting means.

230.208 Protection Requirements. A short-circuit protective device shall be provided on the load side of, or as an integral part of, the service disconnect, and shall protect all ungrounded conductors that it supplies. The protective device shall be capable of detecting and interrupting all values of current, in excess of its trip setting or melting point, that can occur at its location. A fuse rated in continuous amperes not to exceed three times the ampacity of the conductor, or a circuit breaker with a trip setting of not more than six times the ampacity of the conductors, shall be considered as providing the required short-circuit protection.

Informational Note: See Table 310.60(C)(67) through Table 310.60(C)(86) for ampacities of conductors rated 2001 volts and above.

Overcurrent devices shall conform to 230.208(A) and (B).

(A) Equipment Type. Equipment used to protect service-entrance conductors shall meet the requirements of Article 490, Part II.

(B) Enclosed Overcurrent Devices. The restriction to 80 percent of the rating for an enclosed overcurrent device for continuous loads shall not apply to overcurrent devices installed in systems operating at over 600 volts.

230.209 Surge Arresters (Lightning Arresters). Surge arresters installed in accordance with the requirements of Article 280 shall be permitted on each ungrounded overhead service conductor.

230.210 Service Equipment — General Provisions. Service equipment, including instrument transformers, shall conform to Article 490, Part I.

230.211 Metal-Enclosed Switchgear. Metal-enclosed switchgear shall consist of a substantial metal structure and a sheet metal enclosure. Where installed over a combustible floor, suitable protection thereto shall be provided.

230.212 Over 35,000 Volts. Where the voltage exceeds 35,000 volts between conductors that enter a building, they shall terminate in a metal-enclosed switchgear compartment or a vault conforming to the requirements of 450.41 through 450.48.

ARTICLE 240
Overcurrent Protection

I. General

240.1 Scope. Parts I through VII of this article provide the general requirements for overcurrent protection and over-current protective devices not more than 600 volts, nominal. Part VIII covers overcurrent protection for those portions of supervised industrial installations operating at

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voltages of not more than 600 volts, nominal. Part IX covers overcurrent protection over 600 volts, nominal.

Informational Note: Overcurrent protection for conductors and equipment is provided to open the circuit if the current reaches a value that will cause an excessive or dangerous temperature in conductors or conductor insulation. See also 110.9 for requirements for interrupting ratings and 110.10 for requirements for protection against fault currents.

240.2 Definitions.

Current-Limiting Overcurrent Protective Device. A device that, when interrupting currents in its current-limiting range, reduces the current flowing in the faulted circuit to a magnitude substantially less than that obtainable in the same circuit if the device were replaced with a solid conductor having comparable impedance.

Supervised Industrial Installation. For the purposes of Part VIII, the industrial portions of a facility where all of the following conditions are met:

  1. Conditions of maintenance and engineering supervision ensure that only qualified persons monitor and service the system.
  2. The premises wiring system has 2500 kVA or greater of load used in industrial process(es), manufacturing activities, or both, as calculated in accordance with Article 220.
  3. The premises has at least one service or feeder that is more than 150 volts to ground and more than 300 volts phase-to-phase.

This definition excludes installations in buildings used by the industrial facility for offices, warehouses, garages, machine shops, and recreational facilities that are not an integral part of the industrial plant, substation, or control center.

Tap Conductors. As used in this article, a tap conductor is defined as a conductor, other than a service conductor, that has overcurrent protection ahead of its point of supply that exceeds the value permitted for similar conductors that are protected as described elsewhere in 240.4.

240.3 Other Articles. Equipment shall be protected against overcurrent in accordance with the article in this Code that covers the type of equipment specified in Table 240.3.

240.4 Protection of Conductors. Conductors, other than flexible cords, flexible cables, and fixture wires, shall be protected against overcurrent in accordance with their ampacities specified in 310.15, unless otherwise permitted or required in 240.4(A) through (G).

Informational Note: See ICEA P-32-382-2007 for information on allowable short-circuit currents for insulated copper and aluminum conductors.

Table 240.3 Other Articles
Equipment Article
Air-conditioning and refrigerating equipment 440
Appliances 422
Assembly occupancies 518
Audio signal processing, amplification, and reproduction equipment 640
Branch circuits 210
Busways 368
Capacitors 460
Class 1, Class 2, and Class 3 remote-control, signaling, and power-limited circuits 725
Cranes and hoists 610
Electric signs and outline lighting 600
Electric welders 630
Electrolytic cells 668
Elevators, dumbwaiters, escalators, moving walks, wheelchair lifts, and stairway chairlifts 620
Emergency systems 700
Fire alarm systems 760
Fire pumps 695
Fixed electric heating equipment for pipelines and vessels 427
Fixed electric space-heating equipment 424
Fixed outdoor electric deicing and snow-melting equipment 426
Generators 445
Health care facilities 517
Induction and dielectric heating equipment 665
Industrial machinery 670
Luminaires, lampholders, and lamps 410
Motion picture and television studios and similar locations 530
Motors, motor circuits, and controllers 430
Phase converters 455
Pipe organs 650
Receptacles 406
Services 230
Solar photovoltaic systems 690
Switchboards and panelboards 408
Theaters, audience areas of motion picture and television studios, and similar locations 520
Transformers and transformer vaults 450
X-ray equipment 660

(A) Power Loss Hazard. Conductor overload protection shall not be required where the interruption of the circuit would create a hazard, such as in a material-handling magnet circuit or fire pump circuit. Short-circuit protection shall be provided.

Informational Note: See NFPA 20-2010, Standard for the Installation of Stationary Pumps for Fire Protection.

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(B) Overcurrent Devices Rated 800 Amperes or Less.

The next higher standard overcurrent device rating (above the ampacity of the conductors being protected) shall be permitted to be used, provided all of the following conditions are met:

  1. The conductors being protected are not part of a branch circuit supplying more than one receptacle for cord-and-plug-connected portable loads.
  2. The ampacity of the conductors does not correspond with the standard ampere rating of a fuse or a circuit breaker without overload trip adjustments above its rating (but that shall be permitted to have other trip or rating adjustments).
  3. The next higher standard rating selected does not exceed 800 amperes.

(C) Overcurrent Devices Rated over 800 Amperes. Where the overcurrent device is rated over 800 amperes, the ampacity of the conductors it protects shall be equal to or greater than the rating of the overcurrent device defined in 240.6.

(D) Small Conductors. Unless specifically permitted in 240.4(E) or (G), the overcurrent protection shall not exceed that required by (D)(1) through (D)(7) after any correction factors for ambient temperature and number of conductors have been applied.

(1) 18 AWG Copper. 7 amperes, provided all the following conditions are met:

  1. Continuous loads do not exceed 5.6 amperes.
  2. Overcurrent protection is provided by one of the following:
    1. Branch-circuit-rated circuit breakers listed and marked for use with 18 AWG copper wire
    2. Branch-circuit-rated fuses listed and marked for use with 18 AWG copper wire
    3. Class CC, Class J, or Class T fuses

(2) 16 AWG Copper. 10 amperes, provided all the following conditions are met:

  1. Continuous loads do not exceed 8 amperes.
  2. Overcurrent protection is provided by one of the following:
    1. Branch-circuit-rated circuit breakers listed and marked for use with 16 AWG copper wire
    2. Branch-circuit-rated fuses listed and marked for use with 16 AWG copper wire
    3. Class CC, Class J, or Class T fuses

(3) 14 AWG Copper. 15 amperes

(4) 12 AWG Aluminum and Copper-Clad Aluminum. 15 amperes

(5) 12 AWG Copper. 20 amperes

(6) 10 AWG Aluminum and Copper-Clad Aluminum. 25 amperes

(7) 10 AWG Copper. 30 amperes

(E) Tap Conductors. Tap conductors shall be permitted to be protected against overcurrent in accordance with the following:

  1. 210.19(A)(3) and (A)(4), Household Ranges and Cooking Appliances and Other Loads
  2. 240.5(B)(2), Fixture Wire
  3. 240.21, Location in Circuit
  4. 368.17(B), Reduction in Ampacity Size of Busway
  5. 368.17(C), Feeder or Branch Circuits (busway taps)
  6. 430.53(D), Single Motor Taps

(F) Transformer Secondary Conductors. Single-phase (other than 2-wire) and multiphase (other than delta-delta, 3-wire) transformer secondary conductors shall not be considered to be protected by the primary overcurrent protective device. Conductors supplied by the secondary side of a single-phase transformer having a 2-wire (single-voltage) secondary, or a three-phase, delta-delta connected transformer having a 3-wire (single-voltage) secondary, shall be permitted to be protected by overcurrent protection provided on the primary (supply) side of the transformer, provided this protection is in accordance with 450.3 and does not exceed the value determined by multiplying the secondary conductor ampacity by the secondary-to-primary transformer voltage ratio.

(G) Overcurrent Protection for Specific Conductor Applications. Overcurrent protection for the specific conductors shall be permitted to be provided as referenced in Table 240.4(G).

240.5 Protection of Flexible Cords, Flexible Cables, and Fixture Wires. Flexible cord and flexible cable, including tinsel cord and extension cords, and fixture wires shall be protected against overcurrent by either 240.5(A) or (B).

(A) Ampacities. Flexible cord and flexible cable shall be protected by an overcurrent device in accordance with their ampacity as specified in Table 400.5(A)(1) and Table 400.5(A)(2). Fixture wire shall be protected against overcurrent in accordance with its ampacity as specified in Table 402.5. Supplementary overcurrent protection, as covered in 240.10, shall be permitted to be an acceptable means for providing this protection.

(B) Branch-Circuit Overcurrent Device. Flexible cord shall be protected, where supplied by a branch circuit, in accordance with one of the methods described in 240.5(B)(1), (B)(3), or (B)(4). Fixture wire shall be protected, where supplied by a branch circuit, in accordance with 240.5(B)(2).

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Table 240.4(G) Specific Conductor Applications
Conductor Article Section
Air-conditioning and refrigeration equipment circuit conductors 440, Parts III, VI  
Capacitor circuit conductors 460 460.8(B) and 460.25(A)–(D)
Control and instrumentation circuit conductors (Type ITC) 727 727.9
Electric welder circuit conductors 630 630.12 and 630.32
Fire alarm system circuit conductors 760 760.43, 760.45, 760.121, and Chapter 9, Tables 12(A) and 12(B)
Motor-operated appliance circuit conductors 422, Part II  
Motor and motor-control circuit conductors 430, Parts III, IV, V, VI, VII  
Phase converter supply conductors 455 455.7
Remote-control, signaling, and power-limited circuit conductors 725 725.43, 725.45, 725.121, and Chapter 9, Tables 11(A) and 11(B)
Secondary tie conductors 450 450.6

(1) Supply Cord of Listed Appliance or Luminaire. Where flexible cord or tinsel cord is approved for and used with a specific listed appliance or luminaire, it shall be considered to be protected when applied within the appliance or luminaire listing requirements. For the purposes of this section, a luminaire may be either portable or permanent.

(2) Fixture Wire. Fixture wire shall be permitted to be tapped to the branch-circuit conductor of a branch circuit in accordance with the following:

  1. 20-ampere circuits — 18 AWG, up to 15 m (50 ft) of run length
  2. 20-ampere circuits — 16 AWG, up to 30 m (100 ft) of run length
  3. 20-ampere circuits — 14 AWG and larger
  4. 30-ampere circuits — 14 AWG and larger
  5. 40-ampere circuits — 12 AWG and larger
  6. 50-ampere circuits — 12 AWG and larger

(3) Extension Cord Sets. Flexible cord used in listed extension cord sets shall be considered to be protected when applied within the extension cord listing requirements.

(4) Field Assembled Extension Cord Sets. Flexible cord used in extension cords made with separately listed and installed components shall be permitted to be supplied by a branch circuit in accordance with the following:

20-ampere circuits — 16 AWG and larger

240.6 Standard Ampere Ratings.

(A) Fuses and Fixed-Trip Circuit Breakers. The standard ampere ratings for fuses and inverse time circuit breakers shall be considered 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250, 300, 350, 400, 450, 500, 600, 700, 800, 1000, 1200, 1600, 2000, 2500, 3000, 4000, 5000, and 6000 amperes. Additional standard ampere ratings for fuses shall be 1, 3, 6, 10, and 601. The use of fuses and inverse time circuit breakers with nonstandard ampere ratings shall be permitted.

(B) Adjustable-Trip Circuit Breakers. The rating of adjustable-trip circuit breakers having external means for adjusting the current setting (long-time pickup setting), not meeting the requirements of 240.6(C), shall be the maximum setting possible.

(C) Restricted Access Adjustable-Trip Circuit Breakers. A circuit breaker(s) that has restricted access to the adjusting means shall be permitted to have an ampere rating(s) that is equal to the adjusted current setting (long-time pickup setting). Restricted access shall be defined as located behind one of the following:

  1. Removable and sealable covers over the adjusting means
  2. Bolted equipment enclosure doors
  3. Locked doors accessible only to qualified personnel

240.8 Fuses or Circuit Breakers in Parallel. Fuses and circuit breakers shall be permitted to be connected in parallel where they are factory assembled in parallel and listed as a unit. Individual fuses, circuit breakers, or combinations thereof shall not otherwise be connected in parallel.

240.9 Thermal Devices. Thermal relays and other devices not designed to open short circuits or ground faults shall not be used for the protection of conductors against over-current due to short circuits or ground faults, but the use of such devices shall be permitted to protect motor branch-circuit conductors from overload if protected in accordance with 430.40.

240.10 Supplementary Overcurrent Protection. Where supplementary overcurrent protection is used for luminaires, appliances, and other equipment or for internal circuits and components of equipment, it shall not be used as a substitute for required branch-circuit overcurrent devices or in place of the required branch-circuit protection. Supplementary overcurrent devices shall not be required to be readily accessible.

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240.12 Electrical System Coordination. Where an orderly shutdown is required to minimize the hazard(s) to personnel and equipment, a system of coordination based on the following two conditions shall be permitted:

  1. Coordinated short-circuit protection
  2. Overload indication based on monitoring systems or devices

Informational Note: The monitoring system may cause the condition to go to alarm, allowing corrective action or an orderly shutdown, thereby minimizing personnel hazard and equipment damage.

240.13 Ground-Fault Protection of Equipment. Ground-fault protection of equipment shall be provided in accordance with the provisions of 230.95 for solidly grounded wye electrical systems of more than 150 volts to ground but not exceeding 600 volts phase-to-phase for each individual device used as a building or structure main disconnecting means rated 1000 amperes or more.

The provisions of this section shall not apply to the disconnecting means for the following:

  1. Continuous industrial processes where a nonorderly shutdown will introduce additional or increased hazards
  2. Installations where ground-fault protection is provided by other requirements for services or feeders
  3. Fire pumps

240.15 Ungrounded Conductors.

(A) Overcurrent Device Required. A fuse or an overcurrent trip unit of a circuit breaker shall be connected in series with each ungrounded conductor. A combination of a current transformer and overcurrent relay shall be considered equivalent to an overcurrent trip unit.

Informational Note: For motor circuits, see Parts III, IV, V, and XI of Article 430.

(B) Circuit Breaker as Overcurrent Device. Circuit breakers shall open all ungrounded conductors of the circuit both manually and automatically unless otherwise permitted in 240.15(B)(1), (B)(2), (B)(3), and (B)(4).

(1) Multiwire Branch Circuit. Individual single-pole circuit breakers, with identified handle ties, shall be permitted as the protection for each ungrounded conductor of multi-wire branch circuits that serve only single-phase line-to-neutral loads.

(2) Grounded Single-Phase Alternating-Current Circuits. In grounded systems, individual single-pole circuit breakers rated 120/240 volts ac, with identified handle ties, shall be permitted as the protection for each ungrounded conductor for line-to-line connected loads for single-phase circuits.

(3) 3-Phase and 2-Phase Systems. For line-to-line loads in 4-wire, 3-phase systems or 5-wire, 2-phase systems, individual single-pole circuit breakers rated 120/240 volts ac with identified handle ties shall be permitted as the protection for each ungrounded conductor, if the systems have a grounded neutral point and the voltage to ground does not exceed 120 volts.

(4) 3-Wire Direct-Current Circuits. Individual single-pole circuit breakers rated 125/250 volts dc with identified handle ties shall be permitted as the protection for each ungrounded conductor for line-to-line connected loads for 3-wire, direct-current circuits supplied from a system with a grounded neutral where the voltage to ground does not exceed 125 volts.

II. Location

240.21 Location in Circuit. Overcurrent protection shall be provided in each ungrounded circuit conductor and shall be located at the point where the conductors receive their supply except as specified in 240.21(A) through (H). Conductors supplied under the provisions of 240.21(A) through (H) shall not supply another conductor except through an overcurrent protective device meeting the requirements of 240.4.

(A) Branch-Circuit Conductors. Branch-circuit tap conductors meeting the requirements specified in 210.19 shall be permitted to have overcurrent protection as specified in 210.20.

(B) Feeder Taps. Conductors shall be permitted to be tapped, without overcurrent protection at the tap, to a feeder as specified in 240.21(B)(1) through (B)(5). The provisions of 240.4(B) shall not be permitted for tap conductors.

(1) Taps Not over 3 m (10 ft) Long. If the length of the tap conductors does not exceed 3 m (10 ft) and the tap conductors comply with all of the following:

  1. The ampacity of the tap conductors is
    1. Not less than the combined calculated loads on the circuits supplied by the tap conductors, and
    2. Not less than the rating of the device supplied by the tap conductors or not less than the rating of the overcurrent protective device at the termination of the tap conductors.
  2. The tap conductors do not extend beyond the switchboard, panelboard, disconnecting means, or control devices they supply.
  3. Except at the point of connection to the feeder, the tap conductors are enclosed in a raceway, which shall extend from the tap to the enclosure of an enclosed switchboard, panelboard, or control devices, or to the back of an open switchboard. 70-92
  4. For field installations, if the tap conductors leave the enclosure or vault in which the tap is made, the ampacity of the tap conductors is not less than one-tenth of the rating of the overcurrent device protecting the feeder conductors.

Informational Note: For overcurrent protection requirements for panelboards, see 408.36.

(2) Taps Not over 7.5 m (25 ft) Long. Where the length of the tap conductors does not exceed 7.5 m (25 ft) and the tap conductors comply with all the following:

  1. The ampacity of the tap conductors is not less than one-third of the rating of the overcurrent device protecting the feeder conductors.
  2. The tap conductors terminate in a single circuit breaker or a single set of fuses that limit the load to the ampacity of the tap conductors. This device shall be permitted to supply any number of additional overcurrent devices on its load side.
  3. The tap conductors are protected from physical damage by being enclosed in an approved raceway or by other approved means.

(3) Taps Supplying a Transformer [Primary Plus Secondary Not over 7.5 m (25 ft) Long]. Where the tap conductors supply a transformer and comply with all the following conditions:

  1. The conductors supplying the primary of a transformer have an ampacity at least one-third the rating of the overcurrent device protecting the feeder conductors.
  2. The conductors supplied by the secondary of the transformer shall have an ampacity that is not less than the value of the primary-to-secondary voltage ratio multiplied by one-third of the rating of the overcurrent device protecting the feeder conductors.
  3. The total length of one primary plus one secondary conductor, excluding any portion of the primary conductor that is protected at its ampacity, is not over 7.5 m (25 ft).
  4. The primary and secondary conductors are protected from physical damage by being enclosed in an approved raceway or by other approved means.
  5. The secondary conductors terminate in a single circuit breaker or set of fuses that limit the load current to not more than the conductor ampacity that is permitted by 310.15.

(4) Taps over 7.5 m (25 ft) Long. Where the feeder is in a high bay manufacturing building over 11 m (35 ft) high at walls and the installation complies with all the following conditions:

  1. Conditions of maintenance and supervision ensure that only qualified persons service the systems.
  2. The tap conductors are not over 7.5 m (25 ft) long horizontally and not over 30 m (100 ft) total length.
  3. The ampacity of the tap conductors is not less than one-third the rating of the overcurrent device protecting the feeder conductors.
  4. The tap conductors terminate at a single circuit breaker or a single set of fuses that limit the load to the ampacity of the tap conductors. This single overcurrent device shall be permitted to supply any number of additional overcurrent devices on its load side.
  5. The tap conductors are protected from physical damage by being enclosed in an approved raceway or by other approved means.
  6. The tap conductors are continuous from end-to-end and contain no splices.
  7. The tap conductors are sized 6 AWG copper or 4 AWG aluminum or larger.
  8. The tap conductors do not penetrate walls, floors, or ceilings.
  9. The tap is made no less than 9 m (30 ft) from the floor.

(5) Outside Taps of Unlimited Length. Where the conductors are located outdoors of a building or structure, except at the point of load termination, and comply with all of the following conditions:

  1. The conductors are protected from physical damage in an approved manner.
  2. The conductors terminate at a single circuit breaker or a single set of fuses that limit the load to the ampacity of the conductors. This single overcurrent device shall be permitted to supply any number of additional over-current devices on its load side.
  3. The overcurrent device for the conductors is an integral part of a disconnecting means or shall be located immediately adjacent thereto.
  4. The disconnecting means for the conductors is installed at a readily accessible location complying with one of the following:
    1. Outside of a building or structure
    2. Inside, nearest the point of entrance of the conductors
    3. Where installed in accordance with 230.6, nearest the point of entrance of the conductors

(C) Transformer Secondary Conductors. A set of conductors feeding a single load, or each set of conductors feeding separate loads, shall be permitted to be connected to a transformer secondary, without overcurrent protection at the secondary, as specified in 240.21(C)(1) through (C)(6). The provisions of 240.4(B) shall not be permitted for transformer secondary conductors.

Informational Note: For overcurrent protection requirements for transformers, see 450.3.

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(1) Protection by Primary Overcurrent Device. Conductors supplied by the secondary side of a single-phase transformer having a 2-wire (single-voltage) secondary, or a three-phase, delta-delta connected transformer having a 3-wire (single-voltage) secondary, shall be permitted to be protected by overcurrent protection provided on the primary (supply) side of the transformer, provided this protection is in accordance with 450.3 and does not exceed the value determined by multiplying the secondary conductor ampacity by the secondary-to-primary transformer voltage ratio.

Single-phase (other than 2-wire) and multiphase (other than delta-delta, 3-wire) transformer secondary conductors are not considered to be protected by the primary overcurrent protective device.

(2) Transformer Secondary Conductors Not over 3 m (10 ft) Long. If the length of secondary conductor does not exceed 3 m (10 ft) and complies with all of the following:

  1. The ampacity of the secondary conductors is
    1. Not less than the combined calculated loads on the circuits supplied by the secondary conductors, and
    2. Not less than the rating of the device supplied by the secondary conductors or not less than the rating of the overcurrent-protective device at the termination of the secondary conductors
  2. The secondary conductors do not extend beyond the switchboard, panelboard, disconnecting means, or control devices they supply.
  3. The secondary conductors are enclosed in a raceway, which shall extend from the transformer to the enclosure of an enclosed switchboard, panelboard, or control devices or to the back of an open switchboard.
  4. For field installations where the secondary conductors leave the enclosure or vault in which the supply connection is made, the rating of the overcurrent device protecting the primary of the transformer, multiplied by the primary to secondary transformer voltage ratio, shall not exceed 10 times the ampacity of the secondary conductor.

Informational Note: For overcurrent protection requirements for panelboards, see 408.36.

(3) Industrial Installation Secondary Conductors Not over 7.5 m (25 ft) Long. For industrial installations only, where the length of the secondary conductors does not exceed 7.5 m (25 ft) and complies with all of the following:

  1. Conditions of maintenance and supervision ensure that only qualified persons service the systems.
  2. The ampacity of the secondary conductors is not less than the secondary current rating of the transformer, and the sum of the ratings of the overcurrent devices does not exceed the ampacity of the secondary conductors.
  3. All overcurrent devices are grouped.
  4. The secondary conductors are protected from physical damage by being enclosed in an approved raceway or by other approved means.

(4) Outside Secondary Conductors. Where the conductors are located outdoors of a building or structure, except at the point of load termination, and comply with all of the following conditions:

  1. The conductors are protected from physical damage in an approved manner.
  2. The conductors terminate at a single circuit breaker or a single set of fuses that limit the load to the ampacity of the conductors. This single overcurrent device shall be permitted to supply any number of additional over-current devices on its load side.
  3. The overcurrent device for the conductors is an integral part of a disconnecting means or shall be located immediately adjacent thereto.
  4. The disconnecting means for the conductors is installed at a readily accessible location complying with one of the following:
    1. Outside of a building or structure
    2. Inside, nearest the point of entrance of the conductors
    3. Where installed in accordance with 230.6, nearest the point of entrance of the conductors

(5) Secondary Conductors from a Feeder Tapped Transformer. Transformer secondary conductors installed in accordance with 240.21(B)(3) shall be permitted to have overcurrent protection as specified in that section.

(6) Secondary Conductors Not over 7.5 m (25 ft) Long. Where the length of secondary conductor does not exceed 7.5 m (25 ft) and complies with all of the following:

  1. The secondary conductors shall have an ampacity that is not less than the value of the primary-to-secondary voltage ratio multiplied by one-third of the rating of the over-current device protecting the primary of the transformer.
  2. The secondary conductors terminate in a single circuit breaker or set of fuses that limit the load current to not more than the conductor ampacity that is permitted by 310.15.
  3. The secondary conductors are protected from physical damage by being enclosed in an approved raceway or by other approved means.

(D) Service Conductors. Service conductors shall be permitted to be protected by overcurrent devices in accordance with 230.91.

(E) Busway Taps. Busways and busway taps shall be permitted to be protected against overcurrent in accordance with 368.17.

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(F) Motor Circuit Taps. Motor-feeder and branch-circuit conductors shall be permitted to be protected against over-current in accordance with 430.28 and 430.53, respectively.

(G) Conductors from Generator Terminals. Conductors from generator terminals that meet the size requirement in 445.13 shall be permitted to be protected against overload by the generator overload protective device(s) required by 445.12.

(H) Battery Conductors. Overcurrent protection shall be permitted to be installed as close as practicable to the storage battery terminals in an unclassified location. Installation of the overcurrent protection within a hazardous (classified) location shall also be permitted.

240.22 Grounded Conductor. No overcurrent device shall be connected in series with any conductor that is intentionally grounded, unless one of the following two conditions is met:

  1. The overcurrent device opens all conductors of the circuit, including the grounded conductor, and is designed so that no pole can operate independently.
  2. Where required by 430.36 or 430.37 for motor overload protection.

240.23 Change in Size of Grounded Conductor. Where a change occurs in the size of the ungrounded conductor, a similar change shall be permitted to be made in the size of the grounded conductor.

240.24 Location in or on Premises.

(A) Accessibility. Overcurrent devices shall be readily accessible and shall be installed so that the center of the grip of the operating handle of the switch or circuit breaker, when in its highest position, is not more than 2.0 m (6 ft 7 in.) above the floor or working platform, unless one of the following applies:

  1. For busways, as provided in 368.17(C).
  2. For supplementary overcurrent protection, as described in 240.10.
  3. For overcurrent devices, as described in 225.40 and 230.92.
  4. For overcurrent devices adjacent to utilization equipment that they supply, access shall be permitted to be by portable means.

(B) Occupancy. Each occupant shall have ready access to all overcurrent devices protecting the conductors supplying that occupancy, unless otherwise permitted in 240.24(B)(1) and (B)(2).

(1) Service and Feeder Overcurrent Devices. Where electric service and electrical maintenance are provided by the building management and where these are under continuous building management supervision, the service overcurrent devices and feeder overcurrent devices supplying more than one occupancy shall be permitted to be accessible only to authorized management personnel in the following:

  1. Multiple-occupancy buildings
  2. Guest rooms or guest suites

(2) Branch-Circuit Overcurrent Devices. Where electric service and electrical maintenance are provided by the building management and where these are under continuous building management supervision, the branch-circuit overcurrent devices supplying any guest rooms or guest suites without permanent provisions for cooking shall be permitted to be accessible only to authorized management personnel.

(C) Not Exposed to Physical Damage. Overcurrent devices shall be located where they will not be exposed to physical damage.

Informational Note: See 110.11, Deteriorating Agents.

(D) Not in Vicinity of Easily Ignitible Material. Overcurrent devices shall not be located in the vicinity of easily ignitible material, such as in clothes closets.

(E) Not Located in Bathrooms. In dwelling units, dormitories, and guest rooms or guest suites, overcurrent devices, other than supplementary overcurrent protection, shall not be located in bathrooms.

(F) Not Located over Steps. Overcurrent devices shall not be located over steps of a stairway.

III. Enclosures

240.30 General.

(A) Protection from Physical Damage. Overcurrent devices shall be protected from physical damage by one of the following:

  1. Installation in enclosures, cabinets, cutout boxes, or equipment assemblies
  2. Mounting on open-type switchboards, panelboards, or control boards that are in rooms or enclosures free from dampness and easily ignitible material and are accessible only to qualified personnel

(B) Operating Handle. The operating handle of a circuit breaker shall be permitted to be accessible without opening a door or cover.

240.32 Damp or Wet Locations. Enclosures for overcurrent devices in damp or wet locations shall comply with 312.2.

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240.33 Vertical Position. Enclosures for overcurrent devices shall be mounted in a vertical position unless that is shown to be impracticable. Circuit breaker enclosures shall be permitted to be installed horizontally where the circuit breaker is installed in accordance with 240.81. Listed busway plug-in units shall be permitted to be mounted in orientations corresponding to the busway mounting position.

IV. Disconnecting and Guarding

240.40 Disconnecting Means for Fuses. Cartridge fuses in circuits of any voltage where accessible to other than qualified persons, and all fuses in circuits over 150 volts to ground, shall be provided with a disconnecting means on their supply side so that each circuit containing fuses can be independently disconnected from the source of power. A current-limiting device without a disconnecting means shall be permitted on the supply side of the service disconnecting means as permitted by 230.82. A single disconnecting means shall be permitted on the supply side of more than one set of fuses as permitted by 430.112, Exception, for group operation of motors and 424.22(C) for fixed electric space-heating equipment.

240.41 Arcing or Suddenly Moving Parts. Arcing or suddenly moving parts shall comply with 240.41(A) and (B).

(A) Location. Fuses and circuit breakers shall be located or shielded so that persons will not be burned or otherwise injured by their operation.

(B) Suddenly Moving Parts. Handles or levers of circuit breakers, and similar parts that may move suddenly in such a way that persons in the vicinity are likely to be injured by being struck by them, shall be guarded or isolated.

V. Plug Fuses, Fuseholders, and Adapters

240.50 General.

(A) Maximum Voltage. Plug fuses shall be permitted to be used in the following circuits:

  1. Circuits not exceeding 125 volts between conductors
  2. Circuits supplied by a system having a grounded neutral point where the line-to-neutral voltage does not exceed 150 volts

(B) Marking. Each fuse, fuseholder, and adapter shall be marked with its ampere rating.

(C) Hexagonal Configuration. Plug fuses of 15-ampere and lower rating shall be identified by a hexagonal configuration of the window, cap, or other prominent part to distinguish them from fuses of higher ampere ratings.

(D) No Energized Parts. Plug fuses, fuseholders, and adapters shall have no exposed energized parts after fuses or fuses and adapters have been installed.

(E) Screw Shell. The screw shell of a plug-type fuseholder shall be connected to the load side of the circuit.

240.51 Edison-Base Fuses.

(A) Classification. Plug fuses of the Edison-base type shall be classified at not over 125 volts and 30 amperes and below.

(B) Replacement Only. Plug fuses of the Edison-base type shall be used only for replacements in existing installations where there is no evidence of overfusing or tampering.

240.52 Edison-Base Fuseholders. Fuseholders of the Edison-base type shall be installed only where they are made to accept Type S fuses by the use of adapters.

240.53 Type S Fuses. Type S fuses shall be of the plug type and shall comply with 240.53(A) and (B).

(A) Classification. Type S fuses shall be classified at not over 125 volts and 0 to 15 amperes, 16 to 20 amperes, and 21 to 30 amperes.

(B) Noninterchangeable. Type S fuses of an ampere classification as specified in 240.53(A) shall not be interchangeable with a lower ampere classification. They shall be designed so that they cannot be used in any fuseholder other than a Type S fuseholder or a fuseholder with a Type S adapter inserted.

240.54 Type S Fuses, Adapters, and Fuseholders.

(A) To Fit Edison-Base Fuseholders. Type S adapters shall fit Edison-base fuseholders.

(B) To Fit Type S Fuses Only. Type S fuseholders and adapters shall be designed so that either the fuseholder itself or the fuseholder with a Type S adapter inserted cannot be used for any fuse other than a Type S fuse.

(C) Nonremovable. Type S adapters shall be designed so that once inserted in a fuseholder, they cannot be removed.

(D) Nontamperable. Type S fuses, fuseholders, and adapters shall be designed so that tampering or shunting (bridging) would be difficult.

(E) Interchangeability. Dimensions of Type S fuses, fuse-holders, and adapters shall be standardized to permit interchangeability regardless of the manufacturer.

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VI. Cartridge Fuses and Fuseholders

240.60 General.

(A) Maximum Voltage — 300-Volt Type. Cartridge fuses and fuseholders of the 300-volt type shall be permitted to be used in the following circuits:

  1. Circuits not exceeding 300 volts between conductors
  2. Single-phase line-to-neutral circuits supplied from a 3-phase, 4-wire, solidly grounded neutral source where the line-to-neutral voltage does not exceed 300 volts

(B) Noninterchangeable — 0-6000-Ampere Cartridge Fuseholders. Fuseholders shall be designed so that it will be difficult to put a fuse of any given class into a fuseholder that is designed for a current lower, or voltage higher, than that of the class to which the fuse belongs. Fuseholders for current-limiting fuses shall not permit insertion of fuses that are not current-limiting.

(C) Marking. Fuses shall be plainly marked, either by printing on the fuse barrel or by a label attached to the barrel showing the following:

  1. Ampere rating
  2. Voltage rating
  3. Interrupting rating where other than 10,000 amperes
  4. Current limiting where applicable
  5. The name or trademark of the manufacturer

The interrupting rating shall not be required to be marked on fuses used for supplementary protection.

(D) Renewable Fuses. Class H cartridge fuses of the renewable type shall be permitted to be used only for replacement in existing installations where there is no evidence of overfusing or tampering.

240.61 Classification. Cartridge fuses and fuseholders shall be classified according to voltage and amperage ranges. Fuses rated 600 volts, nominal, or less shall be permitted to be used for voltages at or below their ratings.

VII. Circuit Breakers

240.80 Method of Operation. Circuit breakers shall be trip free and capable of being closed and opened by manual operation. Their normal method of operation by other than manual means, such as electrical or pneumatic, shall be permitted if means for manual operation are also provided.

240.81 Indicating. Circuit breakers shall clearly indicate whether they are in the open “off” or closed “on” position.

Where circuit breaker handles are operated vertically rather than rotationally or horizontally, the “up” position of the handle shall be the “on” position.

240.82 Nontamperable. A circuit breaker shall be of such design that any alteration of its trip point (calibration) or the time required for its operation requires dismantling of the device or breaking of a seal for other than intended adjustments.

240.83 Marking.

(A) Durable and Visible. Circuit breakers shall be marked with their ampere rating in a manner that will be durable and visible after installation. Such marking shall be permitted to be made visible by removal of a trim or cover.

(B) Location. Circuit breakers rated at 100 amperes or less and 600 volts or less shall have the ampere rating molded, stamped, etched, or similarly marked into their handles or escutcheon areas.

(C) Interrupting Rating. Every circuit breaker having an interrupting rating other than 5000 amperes shall have its interrupting rating shown on the circuit breaker. The interrupting rating shall not be required to be marked on circuit breakers used for supplementary protection.

(D) Used as Switches. Circuit breakers used as switches in 120-volt and 277-volt fluorescent lighting circuits shall be listed and shall be marked SWD or HID. Circuit breakers used as switches in high-intensity discharge lighting circuits shall be listed and shall be marked as HID.

(E) Voltage Marking. Circuit breakers shall be marked with a voltage rating not less than the nominal system voltage that is indicative of their capability to interrupt fault currents between phases or phase to ground.

240.85 Applications. A circuit breaker with a straight voltage rating, such as 240V or 480V, shall be permitted to be applied in a circuit in which the nominal voltage between any two conductors does not exceed the circuit breaker’s voltage rating. A two-pole circuit breaker shall not be used for protecting a 3-phase, corner-grounded delta circuit unless the circuit breaker is marked l(φ)–3(φ) to indicate such suitability.

A circuit breaker with a slash rating, such as 120/240V or 480Y/277V, shall be permitted to be applied in a solidly grounded circuit where the nominal voltage of any conductor to ground does not exceed the lower of the two values of the circuit breaker’s voltage rating and the nominal voltage between any two conductors does not exceed the higher value of the circuit breaker’s voltage rating.

Informational Note: Proper application of molded case circuit breakers on 3-phase systems, other than solidly grounded wye, particularly on corner grounded delta systems, considers the circuit breakers’ individual pole-interrupting capability.

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240.86 Series Ratings. Where a circuit breaker is used on a circuit having an available fault current higher than the marked interrupting rating by being connected on the load side of an acceptable overcurrent protective device having a higher rating, the circuit breaker shall meet the requirements specified in (A) or (B), and (C).

(A) Selected Under Engineering Supervision in Existing Installations. The series rated combination devices shall be selected by a licensed professional engineer engaged primarily in the design or maintenance of electrical installations. The selection shall be documented and stamped by the professional engineer. This documentation shall be available to those authorized to design, install, inspect, maintain, and operate the system. This series combination rating, including identification of the upstream device, shall be field marked on the end use equipment.

For calculated applications, the engineer shall ensure that the downstream circuit breaker(s) that are part of the series combination remain passive during the interruption period of the line side fully rated, current-limiting device.

(B) Tested Combinations. The combination of line-side overcurrent device and load-side circuit breaker(s) is tested and marked on the end use equipment, such as switchboards and panelboards.

Informational Note to (A) and (B): See 110.22 for marking of series combination systems.

(C) Motor Contribution. Series ratings shall not be used where

  1. Motors are connected on the load side of the higher-rated overcurrent device and on the line side of the lower-rated overcurrent device, and
  2. The sum of the motor full-load currents exceeds 1 percent of the interrupting rating of the lower-rated circuit breaker.

240.87 Noninstantaneous Trip. Where a circuit breaker is used without an instantaneous trip, documentation shall be available to those authorized to design, install, operate, or inspect the installation as to the location of the circuit breaker(s).

Where a circuit breaker is utilized without an instantaneous trip, one of the following or approved equivalent means shall be provided:

  1. Zone-selective interlocking
  2. Differential relaying
  3. Energy-reducing maintenance switching with local status indicator

Informational Note: An energy-reducing maintenance switch allows a worker to set a circuit breaker trip unit to “no intentional delay” to reduce the clearing time while the worker is working within an arc-flash boundary as defined in NFPA 70E-2009, Standard for Electrical Safety in the Workplace, and then to set the trip unit back to a normal setting after the potentially hazardous work is complete.

VIII. Supervised Industrial Installations

240.90 General. Overcurrent protection in areas of supervised industrial installations shall comply with all of the other applicable provisions of this article, except as provided in Part VIII. The provisions of Part VIII shall be permitted only to apply to those portions of the electrical system in the supervised industrial installation used exclusively for manufacturing or process control activities.

240.91 Protection of Conductors. Conductors shall be protected in accordance with 240.91(A) or (B).

(A) General. Conductors shall be protected in accordance with 240.4.

(B) Devices Rated Over 800 Amperes. Where the over-current device is rated over 800 amperes, the ampacity of the conductors it protects shall be equal to or greater than 95 percent of the rating of the overcurrent device specified in 240.6 in accordance with (B)(1) and (2).

  1. The conductors are protected within recognized time vs. current limits for short-circuit currents
  2. All equipment in which the conductors terminate is listed and marked for the application

240.92 Location in Circuit. An overcurrent device shall be connected in each ungrounded circuit conductor as required in 240.92(A) through (E).

(A) Feeder and Branch-Circuit Conductors. Feeder and branch-circuit conductors shall be protected at the point the conductors receive their supply as permitted in 240.21 or as otherwise permitted in 240.92(B), (C), (D), or (E).

(B) Feeder Taps. For feeder taps specified in 240.21(B)(2), (B) (3), and (B)(4), the tap conductors shall be permitted to be sized in accordance with Table 240.92(B).

(C) Transformer Secondary Conductors of Separately Derived Systems. Conductors shall be permitted to be connected to a transformer secondary of a separately derived system, without overcurrent protection at the connection, where the conditions of 240.92(C)(1), (C)(2), and (C)(3) are met.

(1) Short-Circuit and Ground-Fault Protection. The conductors shall be protected from short-circuit and ground-fault conditions by complying with one of the following conditions:

  1. The length of the secondary conductors does not exceed 30 m (100 ft) and the transformer primary over-current device has a rating or setting that does not exceed 150 percent of the value determined by multiplying the secondary conductor ampacity by the secondary-to-primary transformer voltage ratio.
  2. The conductors are protected by a differential relay with a trip setting equal to or less than the conductor ampacity. 70-98
    Table 240.92(B) Tap Conductor Short-Circuit Current Ratings.
    Tap conductors are considered to be protected under short-circuit conditions when their short-circuit temperature limit is not exceeded. Conductor heating under short-circuit conditions is determined by (1) or (2):
    1. Short-Circuit Formula for Copper Conductors

           (I2/A2)t = 0.0297 log10 [(T2 + 234)/(T1 + 234)]
    2. Short-Circuit Formula for Aluminum Conductors

           (I2/A2)t = 0.0125 log10 [(T2 + 228)/(T1 + 228)]
    where:
    I = short-circuit current in amperes
    A = conductor area in circular mils
    t = time of short circuit in seconds (for times less than or equal to 10 seconds)
    T1 = initial conductor temperature in degrees Celsius.
    T2 = final conductor temperature in degrees Celsius.
    Copper conductor with paper, rubber, varnished cloth insulation, T2 = 200
    Copper conductor with thermoplastic insulation, T2 = 150
    Copper conductor with cross-linked polyethylene insulation, T2 = 250
    Copper conductor with ethylene propylene rubber insulation, T2 = 250
    Aluminum conductor with paper, rubber, varnished cloth insulation, T2 = 200
    Aluminum conductor with thermoplastic insulation, T2 = 150
    Aluminum conductor with cross-linked polyethylene insulation, T2 = 250
    Aluminum conductor with ethylene propylene rubber insulation, T2 = 250

    Informational Note: A differential relay is connected to be sensitive only to short-circuit or fault currents within the protected zone and is normally set much lower than the conductor ampacity. The differentia! relay is connected to trip protective devices that de-energize the protected conductors if a short-circuit condition occurs.

  3. The conductors shall be considered to be protected if calculations, made under engineering supervision, determine that the system overcurrent devices will protect the conductors within recognized time vs. current limits for all short-circuit and ground-fault conditions.

(2) Overload Protection. The conductors shall be protected against overload conditions by complying with one of the following:

  1. The conductors terminate in a single overcurrent device that will limit the load to the conductor ampacity.
  2. The sum of the overcurrent devices at the conductor termination limits the load to the conductor ampacity. The overcurrent devices shall consist of not more than six circuit breakers or sets of fuses, mounted in a single enclosure, in a group of separate enclosures, or in or on a switchboard. There shall be no more than six over-current devices grouped in any one location.
  3. Overcurrent relaying is connected [with a current transformers), if needed] to sense all of the secondary conductor current and limit the load to the conductor ampacity by opening upstream or downstream devices.
  4. Conductors shall be considered to be protected if calculations, made under engineering supervision, determine that the system overcurrent devices will protect the conductors from overload conditions.

(3) Physical Protection. The secondary conductors are protected from physical damage by being enclosed in an approved raceway or by other approved means.

(D) Outside Feeder Taps. Outside conductors shall be permitted to be tapped to a feeder or to be connected at a transformer secondary, without overcurrent protection at the tap or connection, where all the following conditions are met:

  1. The conductors are protected from physical damage in an approved manner.
  2. The sum of the overcurrent devices at the conductor termination limits the load to the conductor ampacity. The overcurrent devices shall consist of not more than six circuit breakers or sets of fuses mounted in a single enclosure, in a group of separate enclosures, or in or on a switchboard. There shall be no more than six over-current devices grouped in any one location.
  3. The tap conductors are installed outdoors of a building or structure except at the point of load termination.
  4. The overcurrent device for the conductors is an integral part of a disconnecting means or shall be located immediately adjacent thereto.
  5. The disconnecting means for the conductors are installed at a readily accessible location complying with one of the following:
    1. Outside of a building or structure
    2. Inside, nearest the point of entrance of the conductors
    3. Where installed in accordance with 230.6, nearest the point of entrance of the conductors 70-99

(E) Protection by Primary Overcurrent Device. Conductors supplied by the secondary side of a transformer shall be permitted to be protected by overcurrent protection provided on the primary (supply) side of the transformer, provided the primary device time-current protection characteristic, multiplied by the maximum effective primary-to-secondary transformer voltage ratio, effectively protects the secondary conductors.

IX. Overcurrent Protection Over 600 Volts, Nominal

240.100 Feeders and Branch Circuits.

(A) Location and Type of Protection. Feeder and branch-circuit conductors shall have overcurrent protection in each ungrounded conductor located at the point where the conductor receives its supply or at an alternative location in the circuit when designed under engineering supervision that includes but is not limited to considering the appropriate fault studies and time-current coordination analysis of the protective devices and the conductor damage curves. The overcurrent protection shall be permitted to be provided by either 240.100(A)(1) or (A)(2).

(1) Overcurrent Relays and Current Transformers. Circuit breakers used for overcurrent protection of 3-phase circuits shall have a minimum of three overcurrent relay elements operated from three current transformers. The separate overcurrent relay elements (or protective functions) shall be permitted to be part of a single electronic protective relay unit.

On 3-phase, 3-wire circuits, an overcurrent relay element in the residual circuit of the current transformers shall be permitted to replace one of the phase relay elements.

An overcurrent relay element, operated from a current transformer that links all phases of a 3-phase, 3-wire circuit, shall be permitted to replace the residual relay element and one of the phase-conductor current transformers. Where the neutral conductor is not regrounded on the load side of the circuit as permitted in 250.184(B), the current transformer shall be permitted to link all 3-phase conductors and the grounded circuit conductor (neutral).

(2) Fuses. A fuse shall be connected in series with each ungrounded conductor.

(B) Protective Devices. The protective device(s) shall be capable of detecting and interrupting all values of current that can occur at their location in excess of their trip-setting or melting point.

(C) Conductor Protection. The operating time of the protective device, the available short-circuit current, and the conductor used shall be coordinated to prevent damaging or dangerous temperatures in conductors or conductor insulation under short-circuit conditions.

240.101 Additional Requirements for Feeders.

(A) Rating or Setting of Overcurrent Protective Devices. The continuous ampere rating of a fuse shall not exceed three times the ampacity of the conductors. The long-time trip element setting of a breaker or the minimum trip setting of an electronically actuated fuse shall not exceed six times the ampacity of the conductor. For fire pumps, conductors shall be permitted to be protected for overcurrent in accordance with 695.4(B)(2).

(B) Feeder Taps. Conductors tapped to a feeder shall be permitted to be protected by the feeder overcurrent device where that overcurrent device also protects the tap conductor.

ARTICLE 250
Grounding and Bonding

I. General

250.1 Scope. This article covers general requirements for grounding and bonding of electrical installations, and the specific requirements in (1) through (6).

  1. Systems, circuits, and equipment required, permitted, or not permitted to be grounded
  2. Circuit conductor to be grounded on grounded systems
  3. Location of grounding connections
  4. Types and sizes of grounding and bonding conductors and electrodes
  5. Methods of grounding and bonding
  6. Conditions under which guards, isolation, or insulation may be substituted for grounding

Informational Note: See Figure 250.1 for information on the organization of Article 250 covering grounding and bonding requirements.

250.2 Definitions.

Bonding Jumper, Supply-Side. A conductor installed on the supply side of a service or within a service equipment enclosures), or for a separately derived system, that ensures the required electrical conductivity between metal parts required to be electrically connected.

Effective Ground-Fault Current Path. An intentionally constructed, low-impedance electrically conductive path designed and intended to cany current under ground-fault conditions from the point of a ground fault on a wiring system to the electrical supply source and that facilitates the operation of the overcurrent protective device or ground-fault detectors on high-impedance grounded systems.

70-100

Figure 250.1 Grounding and Bonding.

Figure 250.1 Grounding and Bonding.

Ground-Fault Current Path. An electrically conductive path from the point of a ground fault on a wiring system through normally non-current-carrying conductors, equipment, or the earth to the electrical supply source.

Informational Note: Examples of ground-fault current paths could consist of any combination of equipment grounding conductors, metallic raceways, metallic cable sheaths, electrical equipment, and any other electrically conductive material such as metal water and gas piping, steel framing members, stucco mesh, metal ducting, reinforcing steel, shields of communications cables, and the earth itself.

250.3 Application of Other Articles. For other articles applying to particular cases of installation of conductors and equipment, grounding and bonding requirements are identified in Table 250.3 that are in addition to, or modifications of, those of this article.

250.4 General Requirements for Grounding and Bonding. The following general requirements identify what grounding and bonding of electrical systems are required to accomplish. The prescriptive methods contained in Article 250 shall be followed to comply with the performance requirements of this section.

(A) Grounded Systems.

(1) Electrical System Grounding. Electrical systems that are grounded shall be connected to earth in a manner that will limit the voltage imposed by lightning, line surges, or unintentional contact with higher-voltage lines and that will stabilize the voltage to earth during normal operation.

Informational Note: An important consideration for limiting the imposed voltage is the routing of bonding and grounding electrode conductors so that they are not any longer than necessary to complete the connection without disturbing the permanent parts of the installation and so that unnecessary bends and loops are avoided.

(2) Grounding of Electrical Equipment. Normally non-current-carrying conductive materials enclosing electrical conductors or equipment, or forming part of such equipment, shall be connected to earth so as to limit the voltage to ground on these materials.

(3) Bonding of Electrical Equipment. Normally non-current-carrying conductive materials enclosing electrical conductors or equipment, or forming part of such equipment, shall be connected together and to the electrical supply source in a manner that establishes an effective ground-fault current path.

(4) Bonding of Electrically Conductive Materials and Other Equipment. Normally non-current-carrying electrically conductive materials that are likely to become energized shall be connected together and to the electrical supply source in a manner that establishes an effective ground-fault current path.

(5) Effective Ground-Fault Current Path. Electrical equipment and wiring and other electrically conductive material likely to become energized shall be installed in a manner that creates a low-impedance circuit facilitating the operation of the overcurrent device or ground detector for high-impedance grounded systems. It shall be capable of safely carrying the maximum ground-fault current likely to be imposed on it from any point on the wiring system where a ground fault may occur to the electrical supply source. The earth shall not be considered as an effective ground-fault current path.

(B) Ungrounded Systems.

(1) Grounding Electrical Equipment. Non-current-carrying conductive materials enclosing electrical conductors or equipment, or forming part of such equipment, shall be connected to earth in a manner that will limit the voltage imposed by lightning or unintentional contact with higher-voltage lines and limit the voltage to ground on these materials.

(2) Bonding of Electrical Equipment. Non-current-carrying conductive materials enclosing electrical conductors or equipment, or forming part of such equipment, shall be connected

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Table 250.3 Additional Grounding and Bonding Requirements
Conductor/Equipment Article Section
Agricultural buildings   547.9 and 547.10
Audio signal processing, amplification, and reproduction equipment   640.7
Branch circuits   210.5, 210.6, 406.3
Cablebus   370.9
Cable trays 392 392.60
Capacitors   460.10, 460.27
Circuits and equipment operating at less than 50 volts 720  
Communications circuits 800  
Community antenna television and radio distribution systems   820.93, 820.100, 820.103
Conductors for general wiring 310  
Cranes and hoists 610  
Electrically driven or controlled irrigation machines   675.11(C), 675.12, 675.13, 675.14, 675.15
Electric signs and outline lighting 600  
Electrolytic cells 668  
Elevators, dumbwaiters, escalators, moving walks, wheelchair lifts, and stairway chairlifts 620  
Fixed electric heating equipment for pipelines and vessels   427.29, 427.48
Fixed outdoor electric deicing and snow-melting equipment   426.27
Flexible cords and cables   400.22, 400.23
Floating buildings   553.8, 553.10. 553.11
Grounding-type receptacles, adapters, cord connectors, and attachment plugs   406.9
Hazardous (classified) locations 500–517  
Health care facilities 517  
Induction and dielectric heating equipment 665  
Industrial machinery 670  
Information technology equipment   645.15
Intrinsically safe systems   504.50
Luminaires and lighting equipment   410.40, 410.42, 410.46, 410.155(B)
Luminaires, lampholders, and lamps 410  
Marinas and boatyards   555.15
Mobile homes and mobile home park 550  
Motion picture and television studios and similar locations   530.20, 530.64(B)
Motors, motor circuits, and controllers 430  
Natural and artificially made bodies of water 682 682.30, 682.31, 682.32, 682.33
Outlet, device, pull, and junction boxes; conduit bodies; and fittings   314.4, 314.25
Over 600 volts, nominal, underground wiring methods   300.50(B)
Panelboards   408.40
Pipe organs 650  
Radio and television equipment 810  
Receptacles and cord connectors   406.3
Recreational vehicles and recreational vehicle parks 551  
Services 230  
Solar photovoltaic systems   690.41, 690.42, 690.43, 690.45, 690.47
Swimming pools, fountains, and similar installations 680  
Switchboards and panelboards   408.3(D)
Switches   404.12
Theaters, audience areas of motion picture and television studios, and similar locations   520.81
Transformers and transformer vaults   450.10
Use and identification of grounded conductors 200  
X-ray equipment 660 517.78
70-102

together and to the supply system grounded equipment in a manner that creates a low-impedance path for ground-fault current that is capable of carrying the maximum fault current likely to be imposed on it.

(3) Bonding of Electrically Conductive Materials and Other Equipment. Electrically conductive materials that are likely to become energized shall be connected together and to the supply system grounded equipment in a manner that creates a low-impedance path for ground-fault current that is capable of carrying the maximum fault current likely to be imposed on it.

(4) Path for Fault Current. Electrical equipment, wiring, and other electrically conductive material likely to become energized shall be installed in a manner that creates a low-impedance circuit from any point on the wiring system to the electrical supply source to facilitate the operation of overcurrent devices should a second ground fault from a different phase occur on the wiring system. The earth shall not be considered as an effective fault-current path.

250.6 Objectionable Current.

(A) Arrangement to Prevent Objectionable Current. The grounding of electrical systems, circuit conductors, surge arresters, surge-protective devices, and conductive normally non-current-carrying metal parts of equipment shall be installed and arranged in a manner that will prevent objectionable current.

(B) Alterations to Stop Objectionable Current. If the use of multiple grounding connections results in objectionable current, one or more of the following alterations shall be permitted to be made, provided that the requirements of 250.4(A)(5) or (B)(4) are met:

  1. Discontinue one or more but not all of such grounding connections.
  2. Change the locations of the grounding connections.
  3. Interrupt the continuity of the conductor or conductive path causing the objectionable current.
  4. Take other suitable remedial and approved action.

(C) Temporary Currents Not Classified as Objectionable Currents. Temporary currents resulting from abnormal conditions, such as ground faults, shall not be classified as objectionable current for the purposes specified in 250.6(A) and (B).

(D) Limitations to Permissible Alterations. The provisions of this section shall not be considered as permitting electronic equipment from being operated on ac systems or branch circuits that are not connected to an equipment grounding conductor as required by this article. Currents that introduce noise or data errors in electronic equipment shall not be considered the objectionable currents addressed in this section.

(E) Isolation of Objectionable Direct-Current Ground Currents. Where isolation of objectionable dc ground currents from cathodic protection systems is required, a listed ac coupling/dc isolating device shall be permitted in the equipment grounding conductor path to provide an effective return path for ac ground-fault current while blocking dc current.

250.8 Connection of Grounding and Bonding Equipment.

(A) Permitted Methods. Equipment grounding conductors, grounding electrode conductors, and bonding jumpers shall be connected by one of the following means:

  1. Listed pressure connectors
  2. Terminal bars
  3. Pressure connectors listed as grounding and bonding equipment
  4. Exothermic welding process
  5. Machine screw-type fasteners that engage not less than two threads or are secured with a nut
  6. Thread-forming machine screws that engage not less than two threads in the enclosure
  7. Connections that are part of a listed assembly
  8. Other listed means

(B) Methods Not Permitted. Connection devices or fittings that depend solely on solder shall not be used.

250.10 Protection of Ground Clamps and Fittings. Ground clamps or other fittings shall be approved for general use without protection or shall be protected from physical damage as indicated in (1) or (2) as follows:

  1. In installations where they are not likely to be damaged
  2. Where enclosed in metal, wood, or equivalent protective covering

250.12 Clean Surfaces. Nonconductive coatings (such as paint, lacquer, and enamel) on equipment to be grounded shall be removed from threads and other contact surfaces to ensure good electrical continuity or be connected by means of fittings designed so as to make such removal unnecessary.

II. System Grounding

250.20 Alternating-Current Systems to Be Grounded. Alternating-current systems shall be grounded as provided for in 250.20(A), (B), (C), or (D). Other systems shall be permitted to be grounded. If such systems are grounded, they shall comply with the applicable provisions of this article.

70-103

Informational Note: An example of a system permitted to be grounded is a corner-grounded delta transformer connection. See 250.26(4) for conductor to be grounded.

(A) Alternating-Current Systems of Less Than 50 Volts. Alternating-current systems of less than 50 volts shall be grounded under any of the following conditions:

  1. Where supplied by transformers, if the transformer supply system exceeds 150 volts to ground
  2. Where supplied by transformers, if the transformer supply system is ungrounded
  3. Where installed outside as overhead conductors

(B) Alternating-Current Systems of 50 Volts to 1000 Volts. Alternating-current systems of 50 volts to less than 1000 volts that supply premises wiring and premises wiring systems shall be grounded under any of the following conditions:

  1. Where the system can be grounded so that the maximum voltage to ground on the ungrounded conductors does not exceed 150 volts
  2. Where the system is 3-phase, 4-wire, wye connected in which the neutral conductor is used as a circuit conductor
  3. Where the system is 3-phase, 4-wire, delta connected in which the midpoint of one phase winding is used as a circuit conductor

(C) Alternating-Current Systems of 1 kV and Over. Alternating-current systems supplying mobile or portable equipment shall be grounded as specified in 250.188. Where supplying other than mobile or portable equipment, such systems shall be permitted to be grounded.

(D) Impedance Grounded Neutral Systems. Impedance grounded neutral systems shall be grounded in accordance with 250.36 or 250.186.

250.21 Alternating-Current Systems of 50 Volts to Less Than 1000 Volts Not Required to Be Grounded.

(A) General. The following ac systems of 50 volts to less than 1000 volts shall be permitted to be grounded but shall not be required to be grounded:

  1. Electrical systems used exclusively to supply industrial electric furnaces for melting, refining, tempering, and the like
  2. Separately derived systems used exclusively for rectifiers that supply only adjustable-speed industrial drives
  3. Separately derived systems supplied by transformers that have a primary voltage rating less than 1000 volts, provided that all the following conditions are met:
    1. The system is used exclusively for control circuits.
    2. The conditions of maintenance and supervision ensure that only qualified persons service the installation.
    3. Continuity of control power is required.
  4. Other systems that are not required to be grounded in accordance with the requirements of 250.20(B)

(B) Ground Detectors. Ground detectors shall be installed in accordance with 250.21(B)(1) and (B)(2).

  1. Ungrounded alternating current systems as permitted in 250.21(A)(1) through (A)(4) operating at not less than 120 volts and not exceeding 1000 volts shall have ground detectors installed on the system.
  2. The ground detection sensing equipment shall be connected as close as practicable to where the system receives its supply.

(C) Marking. Ungrounded systems shall be legibly marked “Ungrounded System” at the source or first disconnecting means of the system. The marking shall be of sufficient durability to withstand the environment involved.

250.22 Circuits Not to Be Grounded. The following circuits shall not be grounded:

  1. Circuits for electric cranes operating over combustible fibers in Class III locations, as provided in 503.155
  2. Circuits in health care facilities as provided in 517.61 and 517.160
  3. Circuits for equipment within electrolytic cell working zone as provided in Article 668
  4. Secondary circuits of lighting systems as provided in 411.5(A)
  5. Secondary circuits of lighting systems as provided in 680.23(A)(2).

250.24 Grounding Service-Supplied Alternating-Current Systems.

(A) System Grounding Connections. A premises wiring system supplied by a grounded ac service shall have a grounding electrode conductor connected to the grounded service conductor, at each service, in accordance with 250.24(A)(1) through (A)(5).

(1) General. The grounding electrode conductor connection shall be made at any accessible point from the load end of the service drop or service lateral to and including the terminal or bus to which the grounded service conductor is connected at the service disconnecting means.

Informational Note: See definitions of Service Drop and Service Lateral in Article 100.

(2) Outdoor Transformer. Where the transformer supplying the service is located outside the building, at least one additional grounding connection shall be made from the grounded service conductor to a grounding electrode, either at the transformer or elsewhere outside the building.

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Exception: The additional grounding electrode conductor connection shall not be made on high-impedance grounded neutral systems. The system shall meet the requirements of 250.36.

(3) Dual-Fed Services. For services that are dual fed (double ended) in a common enclosure or grouped together in separate enclosures and employing a secondary tie, a single grounding electrode conductor connection to the tie point of the grounded conductor(s) from each power source shall be permitted.

(4) Main Bonding Juniper as Wire or Busbar. Where the main bonding jumper specified in 250.28 is a wire or busbar and is installed from the grounded conductor terminal bar or bus to the equipment grounding terminal bar or bus in the service equipment, the grounding electrode conductor shall be permitted to be connected to the equipment grounding terminal, bar, or bus to which the main bonding jumper is connected.

(5) Load-Side Grounding Connections. A grounded conductor shall not be connected to normally non-current-carrying metal parts of equipment, to equipment grounding conductor(s), or be reconnected to ground on the load side of the service disconnecting means except as otherwise permitted in this article.

Informational Note: See 250.30 for separately derived systems, 250.32 for connections at separate buildings or structures, and 250.142 for use of the grounded circuit conductor for grounding equipment.

(B) Main Bonding Jumper. For a grounded system, an un-spliced main bonding jumper shall be used to connect the equipment grounding conductor(s) and the service-disconnect enclosure to the grounded conductor within the enclosure for each service disconnect in accordance with 250.28.

Exception No. 1: Where more than one service disconnecting means is located in an assembly listed for use as service equipment, an unspliced main bonding jumper shall bond the grounded conductor(s) to the assembly enclosure.

Exception No. 2: Impedance grounded neutral systems shall be permitted to be connected as provided in 250.36 and 250.186.

(C) Grounded Conductor Brought to Service Equipment. Where an ac system operating at less than 1000 volts is grounded at any point, the grounded conductor(s) shall be routed with the ungrounded conductors to each service disconnecting means and shall be connected to each disconnecting means grounded conductor(s) terminal or bus. A main bonding jumper shall connect the grounded conductor(s) to each service disconnecting means enclosure. The grounded conductor(s) shall be installed in accordance with 250.24(C)(1) through (C)(4).

Exception: Where two or more service disconnecting means are located in a single assembly listed for use as service equipment, it shall be permitted to connect the grounded conductor(s) to the assembly common grounded conductor(s) terminal or bus. The assembly shall include a main bonding jumper for connecting the grounded conductor(s) to the assembly enclosure.

(1) Sizing for a Single Raceway. The grounded conductor shall not be smaller than the required grounding electrode conductor specified in Table 250.66 but shall not be required to be larger than the largest ungrounded service-entrance conductor(s). In addition, for sets of ungrounded service-entrance conductors larger than 1100 kcmil copper or 1750 kcmil aluminum, the grounded conductor shall not be smaller than 12½ percent of the circular mil area of the largest set of service-entrance ungrounded conductor(s).

(2) Parallel Conductors in Two or More Raceways. If the ungrounded service-entrance conductors are installed in parallel in two or more raceways, the grounded conductor shall also be installed in parallel. The size of the grounded conductor in each raceway shall be based on the total circular mil area of the parallel ungrounded conductors in the raceway, as indicated in 250.24(C)(1), but not smaller than 1/0 AWG.

Informational Note: See 310.10(H) for grounded conductors connected in parallel.

(3) Delta-Connected Service. The grounded conductor of a 3-phase, 3-wire delta service shall have an ampacity not less than that of the ungrounded conductors.

(4) High Impedance. The grounded conductor on a high-impedance grounded neutral system shall be grounded in accordance with 250.36.

(D) Grounding Electrode Conductor. A grounding electrode conductor shall be used to connect the equipment grounding conductors, the service-equipment enclosures, and, where the system is grounded, the grounded service conductor to the grounding electrode(s) required by Part III of this article. This conductor shall be sized in accordance with 250.66.

High-impedance grounded neutral system connections shall be made as covered in 250.36.

Informational Note: See 250.24(A) for ac system grounding connections.

(E) Ungrounded System Grounding Connections. A premises wiring system that is supplied by an ac service that is ungrounded shall have, at each service, a grounding electrode conductor connected to the grounding electrode(s) required by Part III of this article. The grounding electrode conductor shall be connected to a metal enclosure of the service conductors at

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any accessible point from the load end of the sendee drop or service lateral to the service disconnecting means.

250.26 Conductor to Be Grounded — Alternating-Current Systems. For ac premises wiring systems, the conductor to be grounded shall be as specified in the following:

  1. Single-phase, 2-wire — one conductor
  2. Single-phase, 3-wire — the neutral conductor
  3. Multiphase systems having one wire common to all phases — the common conductor
  4. Multiphase systems where one phase is grounded — one phase conductor
  5. Multiphase systems in which one phase is used as in (2) — the neutral conductor

250.28 Main Bonding Jumper and System Bonding Jumper. For a grounded system, main bonding jumpers and system bonding jumpers shall be installed as follows:

(A) Material. Main bonding jumpers and system bonding jumpers shall be of copper or other corrosion-resistant material. A main bonding jumper and a system bonding jumper shall be a wire, bus, screw, or similar suitable conductor.

(B) Construction. Where a main bonding jumper or a system bonding jumper is a screw only, the screw shall be identified with a green finish that shall be visible with the screw installed.

(C) Attachment. Main bonding jumpers and system bonding jumpers shall be connected in the manner specified by the applicable provisions of 250.8.

(D) Size. Main bonding jumpers and system bonding jumpers shall be sized in accordance with 250.28(D)(1) through (D)(3).

(1) General. Main bonding jumpers and system bonding jumpers shall not be smaller than the sizes shown in Table 250.66. Where the supply conductors are larger than 1100 kcmil copper or 1750 kcmil aluminum, the bonding jumper shall have an area that is not less than 12½ percent of the area of the largest phase conductor except that, where the phase conductors and the bonding jumper are of different materials (copper or aluminum), the minimum size of the bonding jumper shall be based on the assumed use of phase conductors of the same material as the bonding jumper and with an ampacity equivalent to that of the installed phase conductors.

(2) Main Bonding Jumper for Service with More Than One Enclosure. Where a service consists of more than a single enclosure as permitted in 230.71(A), the main bonding jumper for each enclosure shall be sized in accordance with 250.28(D)(1) based on the largest ungrounded service conductor serving that enclosure.

(3) Separately Derived System with More Than One Enclosure. Where a separately derived system supplies more than a single enclosure, the system bonding jumper for each enclosure shall be sized in accordance with 250.28(D)(1) based on the largest ungrounded feeder conductor serving that enclosure, or a single system bonding jumper shall be installed at the source and sized in accordance with 250.28(D)(1) based on the equivalent size of the largest supply conductor determined by the largest sum of the areas of the corresponding conductors of each set.

250.30 Grounding Separately Derived Alternating-Current Systems. In addition to complying with 250.30(A) for grounded systems, or as provided in 250.30(B) for ungrounded systems, separately derived systems shall comply with 250.20, 250.21, 250.22, and 250.26.

Informational Note No. 1: An alternate ac power source, such as an on-site generator, is not a separately derived system if the grounded conductor is solidly interconnected to a service-supplied system grounded conductor. An example of such a situation is where alternate source transfer equipment does not include a switching action in the grounded conductor and allows it to remain solidly connected to the service-supplied grounded conductor when the alternate source is operational and supplying the load served.

Informational Note No. 2: See 445.13 for the minimum size of conductors that carry fault current.

(A) Grounded Systems. A separately derived ac system that is grounded shall comply with 250.30(A)(1) through (A)(8). Except as otherwise permitted in this article, a grounded conductor shall not be connected to normally non-current-carrying metal parts of equipment, be connected to equipment grounding conductors, or be reconnected to ground on the load side of the system bonding jumper.

Informational Note: See 250.32 for connections at separate buildings or structures, and 250.142 for use of the grounded circuit conductor for grounding equipment.

Exception: Impedance grounded neutral system grounding connections shall be made as specified in 250.36 or 250.186, as applicable.

(1) System Bonding Jumper. An unspliced system bonding jumper shall comply with 250.28(A) through (D). This connection shall be made at any single point on the separately derived system from the source to the first system disconnecting means or overcurrent device, or it shall be made at the source of a separately derived system that has no disconnecting means or overcurrent devices, in accordance with 250.30(A)(1)(a) or (b). The system bonding jumper shall remain within the enclosure where it originates.

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If the source is located outside the building or structure supplied, a system bonding jumper shall be installed at the grounding electrode connection in compliance with 250.30(C).

Exception No. 1: For systems installed in accordance with 450.6, a single system bonding jumper connection to the tie point of the grounded circuit conductors from each power source shall be permitted.

Exception No. 2: A system bonding jumper at both the source and the first disconnecting means shall be permitted if doing so does not establish a parallel path for the grounded conductor. If a grounded conductor is used in this manner, it shall not be smaller than the size specified for the system bonding jumper but shall not he required to be larger than the ungrounded conductor(s). For the purposes of this exception, connection through the earth shall not be considered as providing a parallel path.

Exception No. 3: The size of the system bonding jumper for a system that supplies a Class I, Class 2, or Class 3 circuit, and is derived from a transformer rated not more than 1000 volt-amperes, shall not be smaller than the derived ungrounded conductors and shall not be smaller than 14 AWG copper or 12 AWG aluminum.

(a) Installed at the Source. The system bonding jumper shall connect the grounded conductor to the supply-side bonding jumper and the normally non-current-carrying metal enclosure.

(b) Installed at the First Disconnecting Means. The system bonding jumper shall connect the grounded conductor to the supply-side bonding jumper, the disconnecting means enclosure, and the equipment grounding conductor(s).

(2) Supply-Side Bonding Jumper. If the source of a separately derived system and the first disconnecting means are located in separate enclosures, a supply-side bonding jumper shall be installed with the circuit conductors from the source enclosure to the first disconnecting means. A supply-side bonding jumper shall not be required to be larger than the derived ungrounded conductors. The supply-side bonding jumper shall be permitted to be of nonflexible metal raceway type or of the wire or bus type as follows:

(a) A supply-side bonding jumper of the wire type shall comply with 250.102(C). based on the size of the derived ungrounded conductors.

(b) A supply-side bonding jumper of the bus type shall have a cross-sectional area not smaller than a supply-side bonding jumper of the wire type as determined in 250.102(C).

(3) Grounded Conductor. If a grounded conductor is installed and the system bonding jumper connection is not located at the source, 250.30(A)(3)(a) through (A)(3)(d) shall apply.

(a) Sizing for a Single Raceway. The grounded conductor shall not be smaller than the required grounding electrode conductor specified in Table 250.66 but shall not be required to be larger than the largest derived ungrounded conductor(s). In addition, for sets of derived ungrounded conductors larger than 1100 kcmil copper or 1750 kcmil aluminum, the grounded conductor shall not be smaller than 12½ percent of the circular mil area of the largest set of derived ungrounded conductors.

(b) Parallel Conductors in Two or More Raceways. If the ungrounded conductors are installed in parallel in two or more raceways, the grounded conductor shall also be installed in parallel. The size of the grounded conductor in each raceway shall be based on the total circular mil area of the parallel derived ungrounded conductors in the raceway as indicated in 250.30(A)(3)(a), but not smaller than 1/0 AWG.

Informational Note: See 310.10(H) for grounded conductors connected in parallel.

(c) Delta-Connected System. The grounded conductor of a 3-phase, 3-wire delta system shall have an ampacity not less than that of the ungrounded conductors.

(d) Impedance Grounded System. The grounded conductor of an impedance grounded neutral system shall be installed in accordance with 250.36 or 250.186, as applicable.

(4) Grounding Electrode. The grounding electrode shall be as near as practicable to, and preferably in the same area as, the grounding electrode conductor connection to the system. The grounding electrode shall be the nearest of one of the following:

  1. Metal water pipe grounding electrode as specified in 250.52(A)(1)
  2. Structural metal grounding electrode as specified in 250.52(A)(2)

Exception No. 1: Any of the other electrodes identified in 250.52(A) shall be used if the electrodes specified by 250.30(A)(4) are not available.

Exception No. 2 to (1) and (2): If a separately derived system originates in listed equipment suitable for use as service equipment, the grounding electrode used for the service or feeder equipment shall be permitted as the grounding electrode for the separately derived system.

Informational Note No. 1: See 250.104(D) for bonding requirements for interior metal water piping in the area served by separately derived systems.

Informational Note No. 2: See 250.50 and 250.58 for requirements for bonding till electrodes together if located at the same building or structure.

(5) Grounding Electrode Conductor, Single Separately Derived System. A grounding electrode conductor for a single separately derived system shall be sized in accordance with 250.66 for the derived ungrounded conductors,

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It shall be used to connect the grounded conductor of the derived system to the grounding electrode as specified in 250.30(A)(4). This connection shall be made at the same point on the separately derived system where the system bonding jumper is connected.

Exception No. 1: If the system bonding jumper specified in 250.30(A)(1) is a wire or busbar; it shall be permitted to connect the grounding electrode conductor to the equipment grounding terminal, bar, or bus, provided the equipment grounding terminal, bar, or bus is of sufficient size for the separately derived system.

Exception No. 2: If a separately derived system originates in listed equipment suitable as service equipment, the grounding electrode conductor from the service or feeder equipment to the grounding electrode shall be permitted as the grounding electrode conductor for the separately derived system, provided the grounding electrode conductor is of sufficient size for the separately derived system. If the equipment grounding bus internal to the equipment is not smaller than the required grounding electrode conductor for the separately derived system, the grounding electrode connection for the separately derived system shall be permitted to be made to the bus.

Exception No. 3: A grounding electrode conductor shall not be required for a system that supplies a Class I, Class 2, or Class 3 circuit and is derived from a transformer rated not more than 1000 volt-amperes, provided the grounded conductor is bonded to the transformer frame or enclosure by a jumper sized in accordance with 250.30(A)(1), Exception No. 3, and the transformer frame or enclosure is grounded by one of the means specified in 250.134.

(6) Grounding Electrode Conductor, Multiple Separately Derived Systems. A common grounding electrode conductor for multiple separately derived systems shall be permitted. If installed, the common grounding electrode conductor shall be used to connect the grounded conductor of the separately derived systems to the grounding electrode as specified in 250.30(A)(4). A grounding electrode conductor tap shall then be installed from each separately derived system to the common grounding electrode conductor. Each tap conductor shall connect the grounded conductor of the separately derived system to the common grounding electrode conductor. This connection shall be made at the same point on the separately derived system where the system bonding jumper is connected.

Exception No. 1: If the system bonding jumper specified in 250.30(A)(1) is a wire or busbar, it shall be permitted to connect the grounding electrode conductor tap to the equipment grounding terminal, bar, or bus, provided the equipment grounding terminal, bar, or bus is of sufficient size for the separately derived system.

Exception No. 2: A grounding electrode conductor shall not be required for a system that supplies a Class 1, Class 2, or Class 3 circuit and is derived from a transformer rated not more than 1000 volt-amperes, provided the system grounded conductor is bonded to the transformer frame or enclosure by a jumper sized in accordance with 250.30(A)(1), Exception No. 3, and the transformer frame or enclosure is grounded by one of the means specified in 250.134.

(a) Common Grounding Electrode Conductor. The common grounding electrode conductor shall be permitted to be one of the following:

  1. A conductor of the wire type not smaller than 3/0 AWG copper or 250 kcmil aluminum
  2. The metal frame of the building or structure that complies with 250.52(A)(2) or is connected to the grounding electrode system by a conductor that shall not be smaller than 3/0 AWG copper or 250 kcmil aluminum

(b) Tap Conductor Size. Each tap conductor shall be sized in accordance with 250.66 based on the derived ungrounded conductors of the separately derived system it serves.

Exception: If a separately derived system originates in listed equipment suitable as service equipment, the grounding electrode conductor from the sendee or feeder equipment to the grounding electrode shall be permitted as the grounding electrode conductor for the separately derived system, provided the grounding electrode conductor is of sufficient size for the separately derived system. If the equipment ground bus internal to the equipment is not smaller than the required grounding electrode conductor for the separately derived system, the grounding electrode connection for the separately derived system shall be permitted to be made to the bus.

(c) Connections. All tap connections to the common grounding electrode conductor shall be made at an accessible location by one of the following methods:

  1. A connector listed as grounding and bonding equipment.
  2. Listed connections to aluminum or copper busbars not smaller than 6 mm × 50 mm (¼ in. × 2 in.). If aluminum busbars are used, the installation shall comply with 250.64(A).
  3. The exothermic welding process.

Tap conductors shall be connected to the common grounding electrode conductor in such a manner that the common grounding electrode conductor remains without a splice or joint.

(7) Installation. The installation of all grounding electrode conductors shall comply with 250.64(A), (B), (C), and (E).

(8) Bonding. Structural steel and metal piping shall be connected to the grounded conductor of a separately derived system in accordance with 250.104(D).

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(B) Ungrounded Systems. The equipment of an ungrounded separately derived system shall be grounded and bonded as specified in 250.30(B)(1) through (B)(3).

(1) Grounding Electrode Conductor. A grounding electrode conductor, sized in accordance with 250.66 for the largest derived ungrounded conductor (s) or set of derived ungrounded conductors, shall be used to connect the metal enclosures of the derived system to the grounding electrode as specified in 250.30(A)(5) or (6), as applicable. This connection shall be made at any point on the separately derived system from the source to the first system disconnecting means. If the source is located outside the building or structure supplied, a grounding electrode connection shall be made in compliance with 250.30(C).

(2) Grounding Electrode. Except as permitted by 250.34 for portable and vehicle-mounted generators, the grounding electrode shall comply with 250.30(A)(4).

(3) Bonding Path and Conductor. A supply side bonding jumper shall be installed from the source of a separately derived system to the first disconnecting means in compliance with 250.30(A)(2).

(C) Outdoor Source. If the source of the separately derived system is located outside the building or structure supplied, a grounding electrode connection shall be made at the source location to one or more grounding electrodes in compliance with 250.50. In addition, the installation shall comply with 250.30(A) for grounded systems or with 250.30(B) for ungrounded systems.

Exception: The grounding electrode conductor connection for impedance grounded neutral systems shall comply with 250.36 or 250.186. as applicable.

250.32 Buildings or Structures Supplied by a Feeder(s) or Branch Circuit(s).

(A) Grounding Electrode. Building(s) or structure(s) supplied by feeder(s) or branch circuit(s) shall have a grounding electrode or grounding electrode system installed in accordance with Part III of Article 250. The grounding electrode conductor(s) shall be connected in accordance with 250.32(B) or (C). Where there is no existing grounding electrode, the grounding electrode(s) required in 250.50 shall be installed.

Exception: A grounding electrode shall not be required where only a single branch circuit, including a multiwire branch circuit, supplies the building or structure and the branch circuit includes an equipment grounding conductor for grounding the normally non-current-carrying metal parts of equipment.

(B) Grounded Systems.

(1) Supplied by a Feeder or Branch Circuit. An equipment grounding conductor, as described in 250.118, shall be run with the supply conductors and be connected to the building or structure disconnecting means and to the grounding electrode(s). The equipment grounding conductor shall be used for grounding or bonding of equipment, structures, or frames required to be grounded or bonded. The equipment grounding conductor shall be sized in accordance with 250.122. Any installed grounded conductor shall not be connected to the equipment grounding conductor or to the grounding electrode(s).

Exception: For installations made in compliance with previous editions of this Code that permitted such connection, the grounded conductor run with the supply to the building or structure shall be permitted to serve as the ground-fault return path if all of the following requirements continue to be met:

  1. An equipment grounding conductor is not run with the supply to the building or structure.
  2. There are no continuous metallic paths bonded to the grounding system in each building or structure involved.
  3. Ground-fault protection of equipment has not been installed on the supply side of the feeder{s).

If the grounded conductor is used for grounding in accordance with the provision of this exception, the size of the grounded conductor shall not be smaller than the larger of either of the following:

  1. That required by 220.61
  2. That required by 250.122

(2) Supplied by Separately Derived System.

(a) With Overcurrent Protection. If overcurrent protection is provided where the conductors originate, the installation shall comply with 250.32(B)(1).

(b) Without Overcurrent Protection. If overcurrent protection is not provided where the conductors originate, the installation shall comply with 250.30(A). If installed, the supply-side bonding jumper shall be connected to the building or structure disconnecting means and to the grounding electrode(s).

(C) Ungrounded Systems.

(1) Supplied by a Feeder or Branch Circuit. An equipment grounding conductor, as described in 250.118, shall be installed with the supply conductors and be connected to the building or structure disconnecting means and to the grounding electrode(s). The grounding electrocle(s) shall also be connected to the building or structure disconnecting means.

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(2) Supplied by a Separately Derived System.

(a) With Overcurrent Protection. If overcurrent protection is provided where the conductors originate, the installation shall comply with (C)(1).

(b) Without Overcurrent Protection. If overcurrent protection is not provided where the conductors originate, the installation shall comply with 250.30(B). If installed, the supply-side bonding jumper shall be connected to the building or structure disconnecting means and to the grounding electrode(s).

(D) Disconnecting Means Located in Separate Building or Structure on the Same Premises. Where one or more disconnecting means supply one or more additional buildings or structures under single management, and where these disconnecting means are located remote from those buildings or structures in accordance with the provisions of 225.32, Exception No. 1 and No. 2, 700.12(B)(6), 701.12(B)(5), or 702.12, all of the following conditions shall be met:

  1. The connection of the grounded conductor to the grounding electrode, to normally non-current-carrying metal parts of equipment, or to the equipment grounding conductor at a separate building or structure shall not be made.
  2. An equipment grounding conductor for grounding and bonding any normally non-current-carrying metal parts of equipment, interior metal piping systems, and building or structural metal frames is run with the circuit conductors to a separate building or structure and connected to existing grounding electrode(s) required in Part III of this article, or, where there are no existing electrodes, the grounding electrode(s) required in Part III of this article shall be installed where a separate building or structure is supplied by more than one branch circuit.
  3. The connection between the equipment grounding conductor and the grounding electrode at a separate building or structure shall be made in a junction box, panel-board, or similar enclosure located immediately inside or outside the separate building or structure.

(E) Grounding Electrode Conductor. The size of the grounding electrode conductor to the grounding electrode(s) shall not be smaller than given in 250.66, based on the largest ungrounded supply conductor. The installation shall comply with Part III of this article.

250.34 Portable and Vehicle-Mounted Generators.

(A) Portable Generators. The frame of a portable generator shall not be required to be connected to a grounding electrode as defined in 250.52 for a system supplied by the generator under the following conditions:

  1. The generator supplies only equipment mounted on the generator, cord-and-plug-connected equipment through receptacles mounted on the generator, or both, and
  2. The normally non-current-carrying metal parts of equipment and the equipment grounding conductor terminals of the receptacles are connected to the generator frame.

(B) Vehicle-Mounted Generators. The frame of a vehicle shall not be required to be connected to a grounding electrode as defined in 250.52 for a system supplied by a generator located on this vehicle under the following conditions:

  1. The frame of the generator is bonded to the vehicle frame, and
  2. The generator supplies only equipment located on the vehicle or cord-and-plug-connected equipment through receptacles mounted on the vehicle, or both equipment located on the vehicle and cord-and-plug-connected equipment through receptacles mounted on the vehicle or on the generator, and
  3. The normally non-current-carrying metal parts of equipment and the equipment grounding conductor terminals of the receptacles are connected to the generator frame.

(C) Grounded Conductor Bonding. A system conductor that is required to be grounded by 250.26 shall be connected to the generator frame where the generator is a component of a separately derived system.

Informational Note: For grounding portable generators supplying fixed wiring systems, see 250.30.

250.35 Permanently Installed Generators. A conductor that provides an effective ground-fault current path shall be installed with the supply conductors from a permanently installed generator(s) to the first disconnecting mean(s) in accordance with (A) or (B).

(A) Separately Derived System. If the generator is installed as a separately derived system, the requirements in 250.30 shall apply.

(B) Nonseparately Derived System. If the generator is installed as a nonseparately derived system, and overcurrent protection is not integral with the generator assembly, a supply-side bonding jumper shall be installed between the generator equipment grounding terminal and the equipment grounding terminal, bar, or bus of the disconnecting mean(s). It shall be sized in accordance with 250.102(C) based on the size of the conductors supplied by the generator.

250.36 High-Impedance Grounded Neutral Systems. High-impedance grounded neutral systems in which a grounding impedance, usually a resistor, limits the ground-fault current to a low value shall be permitted for 3-phase ac systems of 480 volts to 1000 volts if all the following conditions are met:

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  1. The conditions of maintenance and supervision ensure that only qualified persons service the installation.
  2. Ground detectors are installed on the system.
  3. Line-to-neutral loads are not served.

High-impedance grounded neutral systems shall comply with the provisions of 250.36(A) through (G).

(A) Grounding Impedance Location. The grounding impedance shall be installed between the grounding electrode conductor and the system neutral point. If a neutral point is not available, the grounding impedance shall be installed between the grounding electrode conductor and the neutral point derived from a grounding transformer.

(B) Grounded System Conductor. The grounded system conductor from the neutral point of the transformer or generator to its connection point to the grounding impedance shall be fully insulated.

The grounded system conductor shall have an ampacity of not less than the maximum current rating of the grounding impedance but in no case shall the grounded system conductor be smaller than 8 AWG copper or 6 AWG aluminum or copper-clad aluminum.

(C) System Grounding Connection. The system shall not be connected to ground except through the grounding impedance.

Informational Note: The impedance is normally selected to limit the ground-fault current to a value slightly greater than or equal to the capacitive charging current of the system. This value of impedance will also limit transient overvoltages to safe values. For guidance, refer to criteria for limiting transient overvoltages in ANSI/IEEE 142-1991, Recommended Practice for Grounding of Industrial and Commercial Power Systems.

(D) Neutral Point to Grounding Impedance Conductor Routing. The conductor connecting the neutral point of the transformer or generator to the grounding impedance shall be permitted to be installed in a separate raceway from the ungrounded conductors. It shall not be required to run this conductor with the phase conductors to the first system disconnecting means or overcurrent device.

(E) Equipment Bonding Jumper. The equipment bonding jumper (the connection between the equipment grounding conductors and the grounding impedance) shall be an unspliced conductor run from the first system disconnecting means or overcurrent device to the grounded side of the grounding impedance.

(F) Grounding Electrode Conductor Location. The grounding electrode conductor shall be connected at any point from the grounded side of the grounding impedance to the equipment grounding connection at the service equipment or first system disconnecting means.

(G) Equipment Bonding Jumper Size. The equipment bonding jumper shall be sized in accordance with (1) or (2) as follows:

  1. If the grounding electrode conductor connection is made at the grounding impedance, the equipment bonding jumper shall be sized in accordance with 250.66, based on the size of the service entrance conductors for a service or the derived phase conductors for a separately derived system.
  2. If the grounding electrode conductor is connected at the first system disconnecting means or overcurrent device, the equipment bonding jumper shall be sized the same as the neutral conductor in 250.36(B).

III. Grounding Electrode System and Grounding Electrode Conductor

250.50 Grounding Electrode System. All grounding electrodes as described in 250.52(A)(1) through (A)(7) that are present at each building or structure served shall be bonded together to form the grounding electrode system. Where none of these grounding electrodes exist, one or more of the grounding electrodes specified in 250.52(A)(4) through (A)(8) shall be installed and used.

Exception: Concrete-encased electrodes of existing buildings or structures shall not be required to be part of the grounding electrode system where the steel reinforcing bars or rods are not accessible for use without disturbing the concrete.

250.52 Grounding Electrodes.

(A) Electrodes Permitted for Grounding.

(1) Metal Underground Water Pipe. A metal underground water pipe in direct contact with the earth for 3.0 m (10 ft) or more (including any metal well casing bonded to the pipe) and electrically continuous (or made electrically continuous by bonding around insulating joints or insulating pipe) to the points of connection of the grounding electrode conductor and the bonding conductor(s) or jumper(s). if installed.

(2) Metal Frame of the Building or Structure. The metal frame of the building or structure that is connected to the earth by one or more of the following methods:

  1. At least one structural metal member that is in direct contact with the earth for 3.0 m (10 ft) or more, with or without concrete encasement.
  2. Hold-down bolts securing the structural steel column that are connected to a concrete-encased electrode that complies with 250.52(A)(3) and is located in the support footing or foundation. The hold-down bolts shall be connected to the concrete-encased electrode by welding, exothermic welding, the usual steel tie wires, or other approved means.
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(3) Concrete-Encased Electrode. A concrete-encased electrode shall consist of at least 6.0 m (20 ft) of either (1) or (2):

  1. One or more bare or zinc galvanized or other electrically conductive coated steel reinforcing bars or rods of not less than 13 mm (½ in.) in diameter, installed in one continuous 6.0 m (20 ft) length, or if in multiple pieces connected together by the usual steel tie wires, exothermic welding, welding, or other effective means to create a 6.0 m (20 ft) or greater, length; or
  2. Bare copper conductor not smaller than 4 AWG

    Metallic components shall be encased by at least 50 mm (2 in.) of concrete and shall be located horizontally within that portion of a concrete foundation or footing that is in direct contact with the earth or within vertical foundations or structural components or members that are in direct contact with the earth. If multiple concrete-encased electrodes are present at a building or structure, it shall be permissible to bond only one into the grounding electrode system.

    Informational Note: Concrete installed with insulation, vapor barriers, films or similar items separating the concrete from the earth is not considered to be in “direct contact” with the earth.

(4) Ground Ring. A ground ring encircling the building or structure, in direct contact with the earth, consisting of at least 6.0 m (20 ft) of bare copper conductor not smaller than 2 AWG.

(5) Rod and Pipe Electrodes. Rod and pipe electrodes shall not be less than 2.44 m (8 ft) in length and shall consist of the following materials.

(a) Grounding electrodes of pipe or conduit shall not be smaller than metric designator 21 (trade size ¾) and, where of steel, shall have the outer surface galvanized or otherwise metal-coated for corrosion protection.

(b) Rod-type grounding electrodes of stainless steel and copper or zinc coated steel shall be at least 15.87 mm (⅝ in.) in diameter, unless listed.

(6) Other Listed Electrodes. Other listed grounding electrodes shall be permitted.

(7) Plate Electrodes. Each plate electrode shall expose not less than 0.186 m2 (2 ft2) of surface to exterior soil. Electrodes of bare or conductively coated iron or steel plates shall be at least 6.4 mm (¼ in.) in thickness. Solid, uncoated electrodes of nonferrous metal shall be at least 1.5 mm (0.06 in.) in thickness.

(8) Other Local Metal Underground Systems or Structures. Other local metal underground systems or structures such as piping systems, underground tanks, and underground metal well casings that are not bonded to a metal water pipe.

(B) Not Permitted for Use as Grounding Electrodes. The following systems and materials shall not be used as grounding electrodes:

  1. Metal underground gas piping systems
  2. Aluminum

Informational Note: See 250.104(B) for bonding requirements of gas piping.

250.53 Grounding Electrode System Installation.

Informational Note: See 547.9 and 547.10 for special grounding and bonding requirements for agricultural buildings.

(A) Rod, Pipe, and Plate Electrodes. Rod, pipe, and plate electrodes shall meet the requirements of 250.53(A)(1) through (A)(3).

(1) Below Permanent Moisture Level. If practicable, rod, pipe, and plate electrodes shall be embedded below permanent moisture level. Rod, pipe, and plate electrodes shall be free from nonconductive coatings such as paint or enamel.

(2) Supplemental Electrode Required. A single rod, pipe, or plate electrode shall be supplemented by an additional electrode of a type specified in 250.52(A)(2) through (A)(8). The supplemental electrode shall be permitted to be bonded to one of the following:

  1. Rod, pipe, or plate electrode
  2. Grounding electrode conductor
  3. Grounded service-entrance conductor
  4. Nonflexible grounded service raceway
  5. Any grounded service enclosure

Exception: If a single rod, pipe, or plate grounding electrode has a resistance to earth of 25 ohms or less, the supplemental electrode shall not be required.

(3) Supplemental Electrode. If multiple rod, pipe, or plate electrodes are installed to meet the requirements of this section, they shall not be less than 1.8 m (6 ft) apart.

Informational Note: The paralleling efficiency of rods is increased by spacing them twice the length of the longest rod.

(B) Electrode Spacing. Where more than one of the electrodes of the type specified in 250.52(A)(5) or (A)(7) are used, each electrode of one grounding system (including that used for strike termination devices) shall not be less than 1.83 m (6 ft) from any other electrode of another grounding system. Two or more grounding electrodes that are bonded together shall be considered a single grounding electrode system.

(C) Bonding Jumper. The bonding jumper(s) used to connect the grounding electrodes together to form the grounding electrode system shall be installed in accordance with

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250.64(A), (B), and (E), shall be sized in accordance with 250.66, and shall be connected in the manner specified in 250.70.

(D) Metal Underground Water Pipe. If used as a grounding electrode, metal underground water pipe shall meet the requirements of 250.53(D)(1) and (D)(2).

(1) Continuity. Continuity of the grounding path or the bonding connection to interior piping shall not rely on water meters or filtering devices and similar equipment.

(2) Supplemental Electrode Required. A metal underground water pipe shall be supplemented by an additional electrode of a type specified in 250.52(A)(2) through (A)(8). If the supplemental electrode is of the rod, pipe, or plate type, it shall comply with 250.53(A). The supplemental electrode shall be bonded to one of the following:

  1. Grounding electrode conductor
  2. Grounded service-entrance conductor
  3. Nonflexible grounded service raceway
  4. Any grounded service enclosure
  5. As provided by 250.32(B)

Exception: The supplemental electrode shall be permitted to be bonded to the interior metal water piping at any convenient point as specified in 250.68(C)(1), Exception.

(E) Supplemental Electrode Bonding Connection Size. Where the supplemental electrode is a rod, pipe, or plate electrode, that portion of the bonding jumper that is the sole connection to the supplemental grounding electrode shall not be required to be larger than 6 AWG copper wire or 4 AWG aluminum wire.

(F) Ground Ring. The ground ring shall be buried at a depth below the earth’s surface of not less than 750 mm (30 in.).

(G) Rod and Pipe Electrodes. The electrode shall be installed such that at least 2.44 m (8 ft) of length is in contact with the soil. It shall be driven to a depth of not less than 2.44 m (8 ft) except that, where rock bottom is encountered, the electrode shall be driven at an oblique angle not to exceed 45 degrees from the vertical or, where rock bottom is encountered at an angle up to 45 degrees, the electrode shall be permitted to be buried in a trench that is at least 750 mm (30 in.) deep. The upper end of the electrode shall be flush with or below ground level unless the aboveground end and the grounding electrode conductor attachment are protected against physical damage as specified in 250.10.

(H) Plate Electrode. Plate electrodes shall be installed not less than 750 mm (30 in.) below the surface of the earth.

250.54 Auxiliary Grounding Electrodes. One or more grounding electrodes shall be permitted to be connected to the equipment grounding conductors specified in 250.118 and shall not be required to comply with the electrode bonding requirements of 250.50 or 250.53(C) or the resistance requirements of 250.53(A)(2) Exception, but the earth shall not be used as an effective ground-fault current path as specified in 250.4(A)(5) and 250.4(B)(4).

250.58 Common Grounding Electrode. Where an ac system is connected to a grounding electrode in or at a building or structure, the same electrode shall be used to ground conductor enclosures and equipment in or on that building or structure. Where separate services, feeders, or branch circuits supply a building and are required to be connected to a grounding electrode(s), the same grounding electrode(s) shall be used.

Two or more grounding electrodes that are bonded together shall be considered as a single grounding electrode system in this sense.

250.60 Use of Strike Termination Devices. Conductors and driven pipes, rods, or plate electrodes used for grounding strike termination devices shall not be used in lieu of the grounding electrodes required by 250.50 for grounding wiring systems and equipment. This provision shall not prohibit the required bonding together of grounding electrodes of different systems.

Informational Note No. 1: See 250.106 for spacing from strike termination devices. See 800.100(D), 810.21 (J), and 820.100(D) for bonding of electrodes.

Informational Note No. 2: Bonding together of all separate grounding electrodes will limit potential differences between them and between their associated wiring systems.

250.62 Grounding Electrode Conductor Material. The grounding electrode conductor shall be of copper, aluminum, or copper-clad aluminum. The material selected shall be resistant to any corrosive condition existing at the installation or shall be protected against corrosion. The conductor shall be solid or stranded, insulated, covered, or bare.

250.64 Grounding Electrode Conductor Installation. Grounding electrode conductors at the service, at each building or structure where supplied by a feeder(s) or branch circuit(s), or at a separately derived system shall be installed as specified in 250.64(A) through (F).

(A) Aluminum or Copper-Clad Aluminum Conductors. Bare aluminum or copper-clad aluminum grounding electrode conductors shall not be used where in direct contact with masonry or the earth or where subject to corrosive conditions. Where used outside, aluminum or copper-clad aluminum grounding electrode conductors shall not be terminated within 450 mm (18 in.) of the earth.

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(B) Securing and Protection Against Physical Damage. Where exposed, a grounding electrode conductor or its enclosure shall be securely fastened to the surface on which it is carried. Grounding electrode conductors shall be permitted to be installed on or through framing members. A 4 AWG or larger copper or aluminum grounding electrode conductor shall be protected if exposed to physical damage. A 6 AWG grounding electrode conductor that is free from exposure to physical damage shall be permitted to be run along the surface of the building construction without metal covering or protection if it is securely fastened to the construction: otherwise, it shall be protected in rigid metal conduit (RMC), intermediate metal conduit (IMC), rigid polyvinyl chloride conduit (PVC), reinforced thermosetting resin conduit (RTRC), electrical metallic tubing (EMT), or cable armor. Grounding electrode conductors smaller than 6 AWG shall be protected in RMC, IMC, PVC, RTRC, EMT, or cable armor.

(C) Continuous. Except as provided in 250.30(A)(5) and (A)(6). 250.30(B)(1), and 250.68(C), grounding electrode conductor(s) shall be installed in one continuous length without a splice or joint. If necessary, splices or connections shall be made as permitted in (1) through (4):

  1. Splicing of the wire-type grounding electrode conductor shall be permitted only by irreversible compression-type connectors listed as grounding and bonding equipment or by the exothermic welding process.
  2. Sections of busbars shall be permitted to be connected together to form a grounding electrode conductor.
  3. Bolted, riveted, or welded connections of structural metal frames of buildings or structures.
  4. Threaded, welded, brazed, soldered or bolted-flange connections of metal water piping.

(D) Service with Multiple Disconnecting Means Enclosures. If a service consists of more than a single enclosure as permitted in 230.71(A), grounding electrode connections shall be made in accordance with 250.64(D)(1), (D)(2), or (D)(3).

(1) Common Grounding Electrode Conductor and Taps. A common grounding electrode conductor and grounding electrode conductor taps shall be installed. The common grounding electrode conductor shall be sized in accordance with 250.66, based on the sum of the circular mil area of the largest ungrounded service-entrance conductor(s). If the service-entrance conductors connect directly to a service drop or service lateral, the common grounding electrode conductor shall be sized in accordance with Table 250.66, Note 1.

A grounding electrode conductor tap shall extend to the inside of each service disconnecting means enclosure. The grounding electrode conductor taps shall be sized in accordance with 250.66 for the largest service-entrance conductor serving the individual enclosure. The tap conductors shall be connected to the common grounding electrode conductor by one of the following methods in such a manner that the common grounding electrode conductor remains without a splice or joint:

  1. Exothermic welding.
  2. Connectors listed as grounding and bonding equipment.
  3. Connections to an aluminum or copper busbar not less than 6 mm × 50 mm (¼ in. × 2 in.). The busbar shall be securely fastened and shall be installed in an accessible location. Connections shall be made by a listed connector or by the exothermic Welding process. If aluminum busbars are used, the installation shall comply with 250.64(A).

(2) Individual Grounding Electrode Conductors. A grounding electrode conductor shall be connected between the grounded conductor in each service equipment disconnecting means enclosure and the grounding electrode system. Each grounding electrode conductor shall be sized in accordance with 250.66 based on the service-entrance conductor(s) supplying the individual service disconnecting means.

(3) Common Location. A grounding electrode conductor shall be connected to the grounded service conductor(s) in a wireway or other accessible enclosure on the supply side of the service disconnecting means. The connection shall be made with exothermic welding or a connector listed as grounding and bonding equipment. The grounding electrode conductor shall be sized in accordance with 250.66 based on the service-entrance conductor(s) at the common location where the connection is made.

(E) Enclosures for Grounding Electrode Conductors. Ferrous metal enclosures for grounding electrode conductors shall be electrically continuous from the point of attachment to cabinets or equipment to the grounding electrode and shall be securely fastened to the ground clamp or fitting. Nonferrous metal enclosures shall not be required to be electrically continuous. Ferrous metal enclosures that are not physically continuous from cabinets or equipment to the grounding electrode shall be made electrically continuous by bonding each end of the raceway or enclosure to the grounding electrode conductor. Bonding methods in compliance with 250.92(B) for installations at service equipment locations and with 250.92(B)(2) through (B)(4) for other than service equipment locations shall apply at each end and to all intervening ferrous raceways, boxes, and enclosures between the cabinets or equipment and the grounding electrode. The bonding jumper for a grounding electrode conductor raceway or cable armor shall be the same size as, or larger than, the enclosed grounding electrode conductor. If a raceway is used as protection for a grounding electrode conductor, the installation

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shall comply with the requirements of the appropriate raceway article.

(F) Installation to Electrode(s). Grounding electrode conductor(s) and bonding jumpers interconnecting grounding electrodes shall be installed in accordance with (1), (2), or (3). The grounding electrode conductor shall be sized for the largest grounding electrode conductor required among all the electrodes connected to it.

  1. The grounding electrode conductor shall be permitted to be run to any convenient grounding electrode available in the grounding electrode system where the other electrode(s), if any, is connected by bonding jumpers that are installed in accordance with 250.53(C).
  2. Grounding electrode conductor(s) shall be permitted to be ran to one or more grounding electrode(s) individually.
  3. Bonding jumper(s) from grounding electrode(s) shall be permitted to be connected to an aluminum or copper busbar not less than 6 mm × 50 mm (¼ in. × 2 in.). The busbar shall be securely fastened and shall be installed in an accessible location. Connections shall be made by a listed connector or by the exothermic welding process. The grounding electrode conductor shall be permitted to be run to the busbar. Where aluminum busbars are used, the installation shall comply with 250.64(A).

250.66 Size of Alternating-Current Grounding Electrode Conductor. The size of the grounding electrode conductor at the service, at each building or structure where supplied by a feeder(s) or branch circuit(s), or at a separately derived system of a grounded or ungrounded ac system shall not be less than given in Table 250.66, except as permitted in 250.66(A) through (C).

Informational Note: See 250.24(C) for size of ac system conductor brought to service equipment.

(A) Connections to Rod, Pipe, or Plate Electrodes. Where the grounding electrode conductor is connected to rod, pipe, or plate electrodes as permitted in 250.52(A)(5) or (A)(7), that portion of the conductor that is the sole connection to the grounding electrode shall not be required to be larger than 6 AWG copper wire or 4 AWG aluminum wire.

(B) Connections to Concrete-Encased Electrodes. Where the grounding electrode conductor is connected to a concrete-encased electrode as permitted in 250.52(A)(3), that portion of the conductor that is the sole connection to the grounding electrode shall not be required to be larger than 4 AWG copper wire.

(C) Connections to Ground Rings. Where the grounding electrode conductor is connected to a ground ring as permitted in 250.52(A)(4), that portion of the conductor that is the sole connection to the grounding electrode shall not be required to be larger than the conductor used for the ground ring.

Table 250.66 Grounding Electrode Conductor for Alternating-Current Systems
Size of Largest Ungrounded Service-Entrance Conductor or Equivalent Area for Parallel Conductorsa (AWG/kcmil) Size of Grounding Electrode Conductor (AWG/kcmil)
Copper Aluminum or Copper-Clad Aluminum Copper Aluminum or Copper-Clad Aluminumb
2 or smaller 1/0 or smaller    8    6
1 or 1/0 2/0 or 3/0    6    4
2/0 or 3/0 4/0 or 250    4    2
Over 3/0 through 350 Over 250 through 500    2 1/0
Over 350 through 600 Over 500 through 900 1/0 3/0
Over 600 through 1100 Over 900 through 1750 2/0 4/0
Over 1100 Over 1750 3/0 250
Notes:
1. Where multiple sets of service-entrance conductors are used as permitted in 230.40, Exception No. 2, the equivalent size of the largest service-entrance conductor shall be determined by the largest sum of the areas of the corresponding conductors of each set.
2. Where there are no service-entrance conductors, the grounding electrode conductor size shall be determined by the equivalent size of the largest service-entrance conductor required for the load to be served.
aThis table also applies to the derived conductors of separately derived ac systems.
bSee installation restrictions in 250.64(A).

250.68 Grounding Electrode Conductor and Bonding Jumper Connection to Grounding Electrodes. The connection of a grounding electrode conductor at the service, at each building or structure where supplied by a feeder(s) or branch circuit(s), or at a separately derived system and associated bonding jumper(s) shall be made as specified 250.68(A) through (C).

(A) Accessibility. All mechanical elements used to terminate a grounding electrode conductor or bonding jumper to a grounding electrode shall be accessible.

Exception No. 1: An encased or buried connection to a concrete-encased, driven, or buried grounding electrode shall not be required to be accessible.

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Exception No. 2: Exothermic or irreversible compression connections used at terminations, together with the mechanical means used to attach such terminations to fire-proofed structural metal whether or not the mechanical means is reversible, shall not be required to be accessible.

(B) Effective Grounding Path. The connection of a grounding electrode conductor or bonding jumper to a grounding electrode shall be made in a manner that will ensure an effective grounding path. Where necessary to ensure the grounding path for a metal piping system used as a grounding electrode, bonding shall be provided around insulated joints and around any equipment likely to be disconnected for repairs or replacement. Bonding jumpers shall be of sufficient length to permit removal of such equipment while retaining the integrity of the grounding path.

(C) Metallic Water Pipe and Structural Metal. Grounding electrode conductors and bonding jumpers shall be permitted to be connected at the following locations and used to extend the connection to an electrode(s):

  1. Interior metal water piping located not more than 1.52 m (5 ft) from the point of entrance to the building shall be permitted to be used as a conductor to interconnect electrodes that are part of the grounding electrode system.

    Exception: In industrial, commercial, and institutional buildings or structures, if conditions of maintenance and supervision ensure that only qualified persons service the installation, interior metal water piping located more than 1.52 m (5 ft) from the point of entrance to the building shall be permitted as a bonding conductor to interconnect electrodes that are part of the grounding electrode system, or as a grounding electrode conductor, if the entire length, other than short sections passing perpendicularly through walls, floors, or ceilings, of the interior metal water pipe that is being used for the conductor is exposed.

  2. The structural frame of a building that is directly connected to a grounding electrode as specified in 250.52(A)(2) or 250.68(C)(2)(a), (b), or (c) shall be permitted as a bonding conductor to interconnect electrodes that are part of the grounding electrode system, or as a grounding electrode conductor.
    1. By connecting the structural metal frame to the reinforcing bars of a concrete-encased electrode, as provided in 250.52(A)(3), or ground ring as pro vided in 250.52(A)(4)
    2. By bonding the structural metal frame to one or more of the grounding electrodes, as specified in 250.52(A)(5) or (A)(7), that comply with (2)
    3. By other approved means of establishing a connection to earth

250.70 Methods of Grounding and Bonding Conductor Connection to Electrodes. The grounding or bonding conductor shall be connected to the grounding electrode by exothermic welding, listed lugs, listed pressure connectors, listed clamps, or other listed means. Connections depending on solder shall not be used. Ground clamps shall be listed for the materials of the grounding electrode and the grounding electrode conductor and, where used on pipe, rod, or other buried electrodes, shall also be listed for direct soil burial or concrete encasement. Not more than one conductor shall be connected to the grounding electrode by a single clamp or fitting unless the clamp or fitting is listed for multiple conductors. One of the following methods shall be used:

  1. A pipe fitting, pipe plug, or other approved device screwed into a pipe or pipe fitting
  2. A listed bolted clamp of cast bronze or brass, or plain or malleable iron
  3. For indoor communications purposes only, a listed sheet metal strap-type ground clamp having a rigid metal base that seats on the electrode and having a strap of such material and dimensions that it is not likely to stretch during or after installation
  4. An equally substantial approved means

IV. Enclosure, Raceway, and Service Cable Connections

250.80 Service Raceways and Enclosures. Metal enclosures and raceways for service conductors and equipment shall be connected to the grounded system conductor if the electrical system is grounded or to the grounding electrode conductor for electrical systems that are not grounded.

Exception: A metal elbow that is installed in an underground nonmetallic raceway and is isolated from possible contact by a minimum cover of 450 mm (18 in.) to any part of the elbow shall not be required to be connected to the grounded system conductor or grounding electrode conductor.

250.84 Underground Service Cable or Raceway.

(A) Underground Service Cable. The sheath or armor of a continuous underground metal-sheathed or armored service cable system that is connected to the grounded system conductor on the supply side shall not be required to be connected to the grounded system conductor at the building or structure. The sheath or armor shall be permitted to be insulated from the interior metal raceway or piping.

(B) Underground Service Raceway Containing Cable. An underground metal service raceway that contains a metal-sheathed or armored cable connected to the grounded system conductor shall not be required to be connected to the grounded system conductor at the building or structure. The sheath or armor shall be permitted to be insulated from the interior metal raceway or piping.

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250.86 Other Conductor Enclosures and Raceways. Except as permitted by 250.112(1), metal enclosures and raceways for other than service conductors shall be connected to the equipment grounding conductor.

Exception No. 1: Metal enclosures and raceways for conductors added to existing installations of open wire, knob-and-tube wiring, and nonmetallic-sheathed cable shall not be required to be connected to the equipment grounding conductor where these enclosures or wiring methods comply with (I) through (4) as follows:

  1. Do not provide an equipment ground
  2. Are in runs of less than 7.5 m (25 ft)
  3. Are free from probable contact with ground, grounded metal, metal lath, or other conductive material
  4. Are guarded against contact by persons

Exception No. 2: Short sections of metal enclosures or raceways used to provide support or protection of cable assemblies from physical damage shall not be required to be connected to the equipment grounding conductor.

Exception No. 3: A metal elbow shall not be required to be connected to the equipment grounding conductor where it is installed in a run of nonmetallic raceway and is isolated from possible contact by a minimum cover of 450 mm (18 in.) to any part of the elbow or is encased in not less than 50 mm (2 in.) of concrete.

V. Bonding

250.90 General. Bonding shall be provided where necessary to ensure electrical continuity and the capacity to conduct safely any fault current likely to be imposed.

250.92 Services.

(A) Bonding of Equipment for Services. The normally non-current-carrying metal parts of equipment indicated in 250.92(A)(1) and (A)(2) shall be bonded together.

  1. All raceways, cable trays, cablebus framework, auxiliary gutters, or service cable armor or sheath that enclose, contain, or support service conductors, except as permitted in 250.80
  2. All enclosures containing service conductors, including meter fittings, boxes, or the like, interposed in the service raceway or armor

(B) Method of Bonding at the Service. Bonding jumpers meeting the requirements of this article shall be used around impaired connections, such as reducing washers or oversized, concentric, or eccentric knockouts. Standard locknuts or bushings shall not be the only means for the bonding required by this section but shall be permitted to be installed to make a mechanical connection of the raceway(s).

Electrical continuity at service equipment, service raceways, and service conductor enclosures shall be ensured by one of the following methods:

  1. Bonding equipment to the grounded service conductor in a manner provided in 250.8
  2. Connections utilizing threaded couplings or threaded hubs on enclosures if made up wrenchtight
  3. Threadless couplings and connectors if made up tight for metal raceways and metal-clad cables
  4. Other listed devices, such as bonding-type locknuts, bushings, or bushings with bonding jumpers

250.94 Bonding for Other Systems. An intersystem bonding termination for connecting intersystem bonding conductors required for other systems shall be provided external to enclosures at the service equipment or metering equipment enclosure and at the disconnecting means for any additional buildings or structures. The intersystem bonding termination shall comply with the following:

  1. Be accessible for connection and inspection.
  2. Consist of a set of terminals with the capacity for connection of not less than three intersystem bonding conductors.
  3. Not interfere with opening the enclosure for a service, building or structure disconnecting means, or metering equipment.
  4. At the service equipment, be securely mounted and electrically connected to an enclosure for the service equipment, to the meter enclosure, or to an exposed nonflexible metallic service raceway, or be mounted at one of these enclosures and be connected to the enclosure or to the grounding electrode conductor with a minimum 6 AWG copper conductor
  5. At the disconnecting means for a building or structure, be securely mounted and electrically connected to the metallic enclosure for the building or structure disconnecting means, or be mounted at the disconnecting means and be connected to the metallic enclosure or to the grounding electrode conductor with a minimum 6 AWG copper conductor.
  6. The terminals shall be listed as grounding and bonding equipment.

Exception: In existing buildings or structures where any of the intersystem bonding and grounding electrode conductors required by 770.100(B)(2), 800.100(B)(2), 810.21(F)(2), 820.100(B)(2), and 830.100(B)(2) exist, installation of the intersystem bonding termination is not required. An accessible means external to enclosures for connecting intersystem bonding and grounding electrode conductors shall be permitted at the service equipment and at the disconnecting means for any additional buildings or structures by at least one of the following means:

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  1. Exposed nonjiexible metallic raceways
  2. An exposed grounding electrode conductor
  3. Approved means for the external connection of a copper or other corrosion-resistant bonding or grounding electrode conductor to the grounded raceway or equipment

Informational Note No. 1: A 6 AWG copper conductor with one end bonded to the grounded nonflexible metallic raceway or equipment and with 150 mm (6 in.) or more of the other end made accessible on the outside wall is an example of the approved means covered in 250.94, Exception item (3).

Informational Note No. 2: See 770.100, 800.100, 810.21, 820.100, and 830.100 for intersystem bonding and grounding requirements for conductive optical fiber cables, communications circuits, radio and television equipment, CATV circuits and network-powered broadband communications systems, respectively.

250.96 Bonding Other Enclosures.

(A) General. Metal raceways, cable trays, cable armor, cable sheath, enclosures, frames, fittings, and other metal non-current-carrying parts that are to serve as equipment grounding conductors, with or without the use of supplementary equipment grounding conductors, shall be bonded where necessary to ensure electrical continuity and the capacity to conduct safely any fault current likely to be imposed on them. Any nonconductive paint, enamel, or similar coating shall be removed at threads, contact points, and contact surfaces or be connected by means of fittings designed so as to make such removal unnecessary.

(B) Isolated Grounding Circuits. Where installed for the reduction of electrical noise (electromagnetic interference) on the grounding circuit, an equipment enclosure supplied by a branch circuit shall be permitted to be isolated from a raceway containing circuits supplying only that equipment by one or more listed nonmetallic raceway fittings located at the point of attachment of the raceway to the equipment enclosure. The metal raceway shall comply with provisions of this article and shall be supplemented by an internal insulated equipment grounding conductor installed in accordance with 250.146(D) to ground the equipment enclosure.

Informational Note: Use of an isolated equipment grounding conductor does not relieve the requirement for grounding the raceway system.

250.97 Bonding for Over 250 Volts. For circuits of over 250 volts to ground, the electrical continuity of metal raceways and cables with metal sheaths that contain any conductor other than service conductors shall be ensured by one or more of the methods specified for services in 250.92(B), except for (B)(1).

Exception: Where oversized, concentric, or eccentric knockouts are not encountered, or where a box or enclosure with concentric or eccentric knockouts is listed to provide a reliable bonding connection, the following methods shall be permitted:

  1. Threadless couplings and connectors for cables with metal sheaths
  2. Two locknuts, on rigid metal conduit or intermediate metal conduit, one inside and one outside of boxes and cabinets
  3. Fittings with shoulders that seat firmly against the box or cabinet, such as electrical metallic tubing connectors, flexible metal conduit connectors, and cable connectors, with one locknut on the inside of boxes and cabinets
  4. Listed fittings

250.98 Bonding Loosely Jointed Metal Raceways. Expansion fittings and telescoping sections of metal raceways shall be made electrically continuous by equipment bonding jumpers or other means.

250.100 Bonding in Hazardous (Classified) Locations. Regardless of the voltage of the electrical system, the electrical continuity of non-current-carrying metal parts of equipment, raceways, and other enclosures in any hazardous (classified) location as defined in 500.5 shall be ensured by any of the bonding methods specified in 250.92(B)(2) through (B)(4). One or more of these bonding methods shall be used whether or not equipment grounding conductors of the wire type are installed.

250.102 Bonding Conductors and Jumpers.

(A) Material. Bonding jumpers shall be of copper or other corrosion-resistant material. A bonding juniper shall be a wire, bus, screw, or similar suitable conductor.

(B) Attachment. Bonding jumpers shall be attached in the manner specified by the applicable provisions of 250.8 for circuits and equipment and by 250.70 for grounding electrodes.

(C) Size — Supply-Side Bonding Jumper.

(1) Size for Supply Conductors in a Single Raceway or Cable. The supply-side bonding jumper shall not be smaller than the sizes shown in Table 250.66 for grounding electrode conductors. Where the ungrounded supply conductors are larger than 1100 kcmil copper or 1750 kcmil aluminum, the supply-side bonding jumper shall have an area not less than 12½ percent of the area of the largest set of ungrounded supply conductors.

(2) Size for Parallel Conductor Installations. Where the ungrounded supply conductors are paralleled in two or more raceways or cables, and an individual supply-side

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bonding jumper is used for bonding these raceways or cables, the size of the supply-side bonding jumper for each raceway or cable shall be selected from Table 250.66 based on the size of the ungrounded supply conductors in each raceway or cable. A single supply-side bonding jumper installed for bonding two or more raceways or cables shall be sized in accordance with 250.102(C)(1).

(3) Different Materials. Where the ungrounded supply conductors and the supply-side bonding jumper are of different materials (copper or aluminum), the minimum size of the supply-side bonding jumper shall be based on the assumed use of ungrounded conductors of the same material as the supply-side bonding jumper and with an ampacity equivalent to that of the installed ungrounded supply conductors.

(D) Size — Equipment Bonding Jumper on Load Side of an Overcurrent Device. The equipment bonding jumper on the load side of an overcurrent device(s) shall be sized in accordance with 250.122.

A single common continuous equipment bonding jumper shall be permitted to connect two or more raceways or cables if the bonding jumper is sized in accordance with 250.122 for the largest overcurrent device supplying circuits therein.

(E) Installation. Bonding jumpers or conductors and equipment bonding jumpers shall be permitted to be installed inside or outside of a raceway or an enclosure.

(1) Inside a Raceway or an Enclosure. If installed inside a raceway, equipment bonding jumpers and bonding jumpers or conductors shall comply with the requirements of 250.119 and 250.148.

(2) Outside a Raceway or an Enclosure. If installed on the outside, the length of the bonding jumper or conductor or equipment bonding jumper shall not exceed 1.8 m (6 ft) and shall be routed with the raceway or enclosure.

Exception: An equipment bonding jumper or supply-side bonding jumper longer than 1.8 m (6 ft) shall be permitted at outside pole locations for the purpose of bonding or grounding isolated sections of metal raceways or elbows installed in exposed risers of metal conduit or other metal raceway, and for bonding grounding electrodes, and shall not be required to be routed with a raceway or enclosure.

(3) Protection. Bonding jumpers or conductors and equipment bonding jumpers shall be installed in accordance with 250.64(A) and (B).

250.104 Bonding of Piping Systems and Exposed Structural Steel.

(A) Metal Water Piping. The metal water piping system shall be bonded as required in (A)(1), (A)(2), or (A)(3) of this section. The bonding jumper(s) shall be installed in accordance with 250.64(A), (B), and (E). The points of attachment of the bonding jumper(s) shall be accessible.

(1) General. Metal water piping system(s) installed in or attached to a building or structure shall be bonded to the service equipment enclosure, the grounded conductor at the service, the grounding electrode conductor where of sufficient size, or to the one or more grounding electrodes used. The bonding jumper(s) shall be sized in accordance with Table 250.66 except as permitted in 250.104(A)(2) and (A)(3).

(2) Buildings of Multiple Occupancy. In buildings of multiple occupancy where the metal water piping system(s) installed in or attached to a building or structure for the individual occupancies is metallically isolated from all other occupancies by use of nonmetallic water piping, the metal water piping system(s) for each occupancy shall be permitted to be bonded to the equipment grounding terminal of the panelboard or switchboard enclosure (other than service equipment) supplying that occupancy. The bonding jumper shall be sized in accordance with Table 250.122, based on the rating of the overcurrent protective device for the circuit supplying the occupancy.

(3) Multiple Buildings or Structures Supplied by a Feeder(s) or Branch Circuit(s). The metal water piping system(s) installed in or attached to a building or structure shall be bonded to the building or structure disconnecting means enclosure where located at the building or structure, to the equipment grounding conductor run with the supply conductors, or to the one or more grounding electrodes used. The bonding jumper(s) shall be sized in accordance with 250.66, based on the size of the feeder or branch circuit conductors that supply the building. The bonding jumper shall not be required to be larger than the largest ungrounded feeder or branch circuit conductor supplying the building.

(B) Other Metal Piping. If installed in, or attached to, a building or structure, a metal piping system(s), including gas piping, that is likely to become energized shall be bonded to the service equipment enclosure; the grounded conductor at the service; the grounding electrode conductor, if of sufficient size; or to one or more grounding electrodes used. The bonding conductor(s) or jumper(s) shall be sized in accordance with 250.122, using the rating of the circuit that is likely to energize the piping system(s). The equipment grounding conductor for the circuit that is likely to energize the piping shall be permitted to serve as the bonding means. The points of attachment of the bonding jumper(s) shall be accessible.

Informational Note No. 1: Bonding all piping and metal air ducts within the premises will provide additional safety.

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Informational Note No. 2: Additional information for gas piping systems can be found in Section 7.13 of NFPA 54-2009, National Fuel Gas Code.

(C) Structural Metal. Exposed structural metal that is interconnected to form a metal building frame and is not intentionally grounded or bonded and is likely to become energized shall be bonded to the service equipment enclosure; the grounded conductor at the service; the disconnecting means for buildings or structures supplied by a feeder or branch circuit; the grounding electrode conductor, if of sufficient size; or to one or more grounding electrodes used. The bonding jumper(s) shall be sized in accordance with Table 250.66 and installed in accordance with 250.64(A), (B), and (E). The points of attachment of the bonding jumper(s) shall be accessible unless installed in compliance with 250.68(A), Exception No. 2.

(D) Separately Derived Systems. Metal water piping systems and structural metal that is interconnected to form a building frame shall be bonded to separately derived systems in accordance with (D)(1) through (D)(3).

(1) Metal Water Piping System(s). The grounded conductor of each separately derived system shall be bonded to the nearest available point of the metal water piping system(s) in the area served by each separately derived system. This connection shall be made at the same point on the separately derived system where the grounding electrode conductor is connected. Each bonding jumper shall be sized in accordance with Table 250.66 based on the largest ungrounded conductor of the separately derived system.

Exception No. 1: A separate bonding jumper to the metal water piping system shall not be required where the metal water piping system is used as the grounding electrode for the separately derived system and the water piping system is in the area served.

Exception No. 2: A separate water piping bonding jumper shall not be required where the metal frame of a building or structure is used as the grounding electrode for a separately derived system and is bonded to the metal water piping in the area served by the separately derived system.

(2) Structural Metal. Where exposed structural metal that is interconnected to form the building frame exists in the area served by the separately derived system, it shall be bonded to the grounded conductor of each separately derived system. This connection shall be made at the same point on the separately derived system where the grounding electrode conductor is connected. Each bonding jumper shall be sized in accordance with Table 250.66 based on the largest ungrounded conductor of the separately derived system.

Exception No. 1: A separate bonding jumper to the building structural metal shall not be required where the metal frame of a building or structure is used as the grounding electrode for the separately derived system.

Exception No. 2: A separate bonding jumper to the building structural metal shall not be required where the water piping of a building or structure is used as the grounding electrode for a separately derived system and is bonded to the building structural metal in the area served by the separately derived system.

(3) Common Grounding Electrode Conductor. Where a common grounding electrode conductor is installed for multiple separately derived systems as permitted by 250.30(A)(6), and exposed structural metal that is interconnected to form the building frame or interior metal piping exists in the area served by the separately derived system, the metal piping and the structural metal member shall be bonded to the common grounding electrode conductor in the area served by the separately derived system.

Exception: A separate bonding jumper from each derived system to metal water piping and to structural metal members shall not be required where the metal water piping and the structural metal members in the area served by the separately derived system are bonded to the common grounding electrode conductor.

250.106 Lightning Protection Systems. The lightning protection system ground terminals shall be bonded to the building or structure grounding electrode system.

Informational Note No. 1: See 250.60 for use of strike termination devices. For further information, see NFPA 780-2011, Standard for the Installation of Lightning Protection Systems, which contains detailed information on grounding, bonding, and sideflash distance from lightning protection systems.

Informational Note No. 2: Metal raceways, enclosures, frames, and other non-current-carrying metal parts of electrical equipment installed on a building equipped with a lightning protection system may require bonding or spacing from the lightning protection conductors in accordance with NFPA 780-2011, Standard for the Installation of Lightning Protection Systems.

VI. Equipment Grounding and Equipment Grounding Conductors

250.110 Equipment Fastened in Place (Fixed) or Connected by Permanent Wiring Methods. Exposed, normally non-current-carrying metal parts of fixed equipment supplied by or enclosing conductors or components that are likely to become energized shall be connected to an equipment grounding conductor under any of the following conditions:

  1. Where within 2.5 m (8 ft) vertically or 1.5 m (5 ft) horizontally of ground or grounded metal objects and subject to contact by persons 70-120
  2. Where located in a wet or damp location and not isolated
  3. Where in electrical contact with metal
  4. Where in a hazardous (classified) location as covered by Articles 500 through 517
  5. Where supplied by a wiring method that provides an equipment grounding conductor, except as permitted by 250.86 Exception No. 2 for short sections of metal enclosures
  6. Where equipment operates with any terminal at over 150 volts to ground

Exception No. 1: If exempted by special permission, the metal frame of electrically heated appliances that have the frame permanently and effectively insulated from ground shall not be required to be grounded.

Exception No. 2: Distribution apparatus, such as transformer and capacitor cases, mounted on wooden poles at a height exceeding 2.5 m (8 ft) above ground or grade level shall not be required to be grounded.

Exception No. 3: Listed equipment protected by a system of double insulation, or its equivalent, shall not be required to be connected to the equipment grounding conductor. Where such a system is employed, the equipment shall be distinctively marked.

250.112 Specific Equipment Fastened in Place (Fixed) or Connected by Permanent Wiring Methods. Except as permitted in 250.112(F) and (I), exposed, normally non-current-carrying metal parts of equipment described in 250.112(A) through (K), and normally non-current-carrying metal parts of equipment and enclosures described in 250.112/L) and (M), shall be connected to an equipment grounding conductor, regardless of voltage.

(A) Switchboard Frames and Structures. Switchboard frames and structures supporting switching equipment, except frames of 2-wire dc switchboards where effectively insulated from ground.

(B) Pipe Organs. Generator and motor frames in an electrically operated pipe organ, unless effectively insulated from ground and the motor driving it.

(C) Motor Frames. Motor frames, as provided by 430.242.

(D) Enclosures for Motor Controllers. Enclosures for motor controllers unless attached to ungrounded portable equipment.

(E) Elevators and Cranes. Electrical equipment for elevators and cranes.

(F) Garages, Theaters, and Motion Picture Studios. Electrical equipment in commercial garages, theaters, and motion picture studios, except pendant lampholders supplied by circuits not over 150 volts to ground.

(G) Electric Signs. Electric signs, outline lighting, and associated equipment as provided in 600.7.

(H) Motion Picture Projection Equipment. Motion picture projection equipment.

(I) Remote-Control, Signaling, and Fire Alarm Circuits. Equipment supplied by Class 1 circuits shall be grounded unless operating at less than 50 volts. Equipment supplied by Class 1 power-limited circuits, by Class 2 and Class 3 remote-control and signaling circuits, and by fire alarm circuits shall be grounded where system grounding is required by Part II or Part VIII of this article.

(J) Luminaires. Luminaires as provided in Part V of Article 410.

(K) Skid-Mounted Equipment. Permanently mounted electrical equipment and skids shall be connected to the equipment grounding conductor sized as required by 250.122.

(L) Motor-Operated Water Pumps. Motor-operated water pumps, including the submersible type.

(M) Metal Well Casings. Where a submersible pump is used in a metal well casing, the well casing shall be connected to the pump circuit equipment grounding conductor.

250.114 Equipment Connected by Cord and Plug. Under any of the conditions described in 250.114(1) through (4), exposed, normally non-current-carrying metal parts of cord-and-plug-connected equipment shall be connected to the equipment grounding conductor.

Exception: Listed tools, listed appliances, and listed equipment covered in 250.114(2) through (4) shall not be required to be connected to an equipment grounding conductor where protected by a system of double insulation or its equivalent. Double insulated equipment shall be distinctively marked.

  1. In hazardous (classified) locations (see Articles 500 through 517)
  2. Where operated at over 150 volts to ground

    Exception No. 1: Motors, where guarded, shall not be required to be connected to an equipment grounding conductor.

    Exception No. 2: Metal frames of electrically heated appliances, exempted by special permission, shall not be required to be connected to an equipment grounding conductor, in which case the frames shall be permanently and effectively insulated from ground.

    70-121
  3. In residential occupancies:
    1. Refrigerators, freezers, and air conditioners
    2. Clothes-washing, clothes-drying, dish-washing machines; ranges; kitchen waste disposers; information technology equipment; sump pumps and electrical aquarium equipment
    3. Hand-held motor-operated tools, stationary and fixed motor-operated tools, and light industrial motor-operated tools
    4. Motor-operated appliances of the following types: hedge clippers, lawn mowers, snow blowers, and wet scrubbers
    5. Portable handlamps
  4. In other than residential occupancies:
    1. Refrigerators, freezers, and air conditioners
    2. Clothes-washing, clothes-drying, dish-washing machines; information technology equipment; sump pumps and electrical aquarium equipment
    3. Hand-held motor-operated tools, stationary and fixed motor-operated tools, and light industrial motor-operated tools
    4. Motor-operated appliances of the following types: hedge clippers, lawn mowers, snow blowers, and wet scrubbers
    5. Portable handlamps
    6. Cord-and-plug-connected appliances used in damp or wet locations or by persons standing on the ground or on metal floors or working inside of metal tanks or boilers
    7. Tools likely to be used in wet or conductive locations

Exception: Tools and portable handlamps likely to be used in wet or conductive locations shall not be required to be connected to an equipment grounding conductor where supplied through an isolating transformer with an ungrounded secondary of not over 50 volts.

250.116 Nonelectrical Equipment. The metal parts of the following nonelectrical equipment described in this section shall be connected to the equipment grounding conductor:

  1. Frames and tracks of electrically operated cranes and hoists
  2. Frames of nonelectrically driven elevator cars to which electrical conductors are attached
  3. Hand-operated metal shifting ropes or cables of electric elevators

    Informational Note: Where extensive metal in or on buildings may become energized and is subject to personal contact, adequate bonding and grounding will provide additional safety.

250.118 Types of Equipment Grounding Conductors. The equipment grounding conductor run with or enclosing the circuit conductors shall be one or more or a combination of the following:

  1. A copper, aluminum, or copper-clad aluminum conductor. This conductor shall be solid or stranded; insulated, covered, or bare; and in the form of a wire or a busbar of any shape.
  2. Rigid metal conduit.
  3. Intermediate metal conduit.
  4. Electrical metallic tubing.
  5. Listed flexible metal conduit meeting all the following conditions:
    1. The conduit is terminated in listed fittings.
    2. The circuit conductors contained in the conduit are protected by overcurrent devices rated at 20 amperes or less.
    3. The combined length of flexible metal conduit and flexible metallic tubing and liquidtight flexible metal conduit in the same ground-fault current path does not exceed 1.8 m (6 ft).
    4. If used to connect equipment where flexibility is necessary to minimize the transmission of vibration from equipment or to provide flexibility for equipment that requires movement after installation, an equipment grounding conductor shall be installed.
  6. Listed liquidtight flexible metal conduit meeting all the following conditions:
    1. The conduit is terminated in listed fittings.
    2. For metric designators 12 through 16 (trade sizes ⅜ through ½), the circuit conductors contained in the conduit are protected by overcurrent devices rated at 20 amperes or less.
    3. For metric designators 21 through 35 (trade sizes ¾ through 1¼), the circuit conductors contained in the conduit are protected by overcurrent devices rated not more than 60 amperes and there is no flexible metal conduit, flexible metallic tubing, or liquidtight flexible metal conduit in trade sizes metric designators 12 through 16 (trade sizes ⅜ through ½) in the ground-fault current path.
    4. The combined length of flexible metal conduit and flexible metallic tubing and liquidtight flexible metal conduit in the same ground-fault current path does not exceed 1.8 m (6 ft).
    5. If used to connect equipment where flexibility is necessary to minimize the transmission of vibration from equipment or to provide flexibility for equipment that requires movement after installation, an equipment grounding conductor shall be installed.
  7. Flexible metallic tubing where the tubing is terminated in listed fittings and meeting the following conditions: 70-122
    1. The circuit conductors contained in the tubing are protected by overcurrent devices rated at 20 amperes or less.
    2. The combined length of flexible metal conduit and flexible metallic tubing and liquidtight flexible metal conduit in the same ground-fault current path does not exceed 1.8 m (6 ft).
  8. Armor of Type AC cable as provided in 320.108.
  9. The copper sheath of mineral-insulated, metal-sheathed cable.
  10. Type MC cable that provides an effective ground-fault current path in accordance with one or more of the following:
    1. It contains an insulated or uninsulated equipment grounding conductor in compliance with 250.118(1)
    2. The combined metallic sheath and uninsulated equipment grounding/bonding conductor of interlocked metal tape-type MC cable that is listed and identified as an equipment grounding conductor
    3. The metallic sheath or the combined metallic sheath and equipment grounding conductors of the smooth or corrugated tube-type MC cable that is listed and identified as an equipment grounding conductor
  11. Cable trays as permitted in 392.10 and 392.60.
  12. Cablebus framework as permitted in 370.3.
  13. Other listed electrically continuous metal raceways and listed auxiliary gutters.
  14. Surface metal raceways listed for grounding.

Informational Note: For effective ground-fault current path, see 250.2 Definition.

250.119 Identification of Equipment Grounding Conductors. Unless required elsewhere in this Code, equipment grounding conductors shall be permitted to be bare, covered, or insulated. Individually covered or insulated equipment grounding conductors shall have a continuous outer finish that is either green or green with one or more yellow stripes except as permitted in this section. Conductors with insulation or individual covering that is green, green with one or more yellow stripes, or otherwise identified as permitted by this section shall not be used for ungrounded or grounded circuit conductors.

Exception: Power-limited Class 2 or Class 3 cables, power-limited fire alarm cables, or communications cables containing only circuits operating at less than 50 volts where connected to equipment not required to be grounded in accordance with 250.112(I) shall be permitted to use a conductor with green insulation or green with one or more yellow stripes for other than equipment grounding purposes.

(A) Conductors Larger Than 6 AWG. Equipment grounding conductors larger than 6 AWG shall comply with 250.119(A)(1) and (A)(2).

  1. An insulated or covered conductor larger than 6 AWG shall be permitted, at the time of installation, to be permanently identified as an equipment grounding conductor at each end and at every point where the conductor is accessible.

    Exception: Conductors larger than 6 AWG shall not be required to be marked in conduit bodies that contain no splices or unused hubs.

  2. Identification shall encircle the conductor and shall be accomplished by one of the following:
    1. Stripping the insulation or covering from the entire exposed length
    2. Coloring the insulation or covering green at the termination
    3. Marking the insulation or covering with green tape or green adhesive labels at the termination

(B) Multiconductor Cable. Where the conditions of maintenance and supervision ensure that only qualified persons service the installation, one or more insulated conductors in a multiconductor cable, at the time of installation, shall be permitted to be permanently identified as equipment grounding conductors at each end and at every point where the conductors are accessible by one of the following means:

  1. Stripping the insulation from the entire exposed length
  2. Coloring the exposed insulation green
  3. Marking the exposed insulation with green tape or green adhesive labels

(C) Flexible Cord. An uninsulated equipment grounding conductor shall be permitted, but, if individually covered, the covering shall have a continuous outer finish that is either green or green with one or more yellow stripes.

250.120 Equipment Grounding Conductor Installation. An equipment grounding conductor shall be installed in accordance with 250.120(A), (B), and (C).

(A) Raceway, Cable Trays, Cable Armor, Cablebus, or Cable Sheaths. Where it consists of a raceway, cable tray, cable armor, cablebus framework, or cable sheath or where it is a wire within a raceway or cable, it shall be installed in accordance with the applicable provisions in this Code using fittings for joints and terminations approved for use with the type raceway or cable used. All connections, joints, and fittings shall be made tight using suitable tools.

Informational Note: See the UL guide information on FHIT systems for equipment grounding conductors installed in a raceway that are part of an electrical circuit protective system or a fire-rated cable listed to maintain circuit integrity.

70-123

(B) Aluminum and Copper-Clad Aluminum Conductors. Equipment grounding conductors of bare or insulated aluminum or copper-clad aluminum shall be permitted. Bare conductors shall not come in direct contact with masonry or the earth or where subject to corrosive conditions. Aluminum or copper-clad aluminum conductors shall not be terminated within 450 mm (18 in.) of the earth.

(C) Equipment Grounding Conductors Smaller Than 6 AWG. Where not routed with circuit conductors as permitted in 250.130(C) and 250.134(B) Exception No. 2, equipment grounding conductors smaller than 6 AWG shall be protected from physical damage by an identified raceway or cable armor unless installed within hollow spaces of the framing members of buildings or structures and where not subject to physical damage.

250.121 Use of Equipment Grounding Conductors. An equipment grounding conductor shall not be used as a grounding electrode conductor.

250.122 Size of Equipment Grounding Conductors.

(A) General. Copper, aluminum, or copper-clad aluminum equipment grounding conductors of the wire type shall not be smaller than shown in Table 250.122, but in no case shall they be required to be larger than the circuit conductors supplying the equipment. Where a cable tray, a raceway, or a cable armor or sheath is used as the equipment grounding conductor, as provided in 250.118 and 250.134(A), it shall comply with 250.4(A)(5) or (B)(4).

Equipment grounding conductors shall be permitted to be sectioned within a multiconductor cable, provided the combined circular mil area complies with Table 250.122.

(B) Increased in Size. Where ungrounded conductors are increased in size, equipment grounding conductors, where installed, shall be increased in size proportionately according to the circular mil area of the ungrounded conductors.

(C) Multiple Circuits. Where a single equipment grounding conductor is run with multiple circuits in the same raceway, cable, or cable tray, it shall be sized for the largest overcurrent device protecting conductors in the raceway, cable, or cable tray. Equipment grounding conductors installed in cable trays shall meet the minimum requirements of 392.10(B)(1)(c).

(D) Motor Circuits. Equipment grounding conductors for motor circuits shall be sized in accordance with (D)(1) or (D)(2).

(1) General. The equipment grounding conductor size shall not be smaller than determined by 250.122(A) based on the rating of the branch-circuit short-circuit and ground-fault protective device.

(2) Instantaneous-Trip Circuit Breaker and Motor Short-Circuit Protector. Where the overcurrent device is an instantaneous-trip circuit breaker or a motor short-circuit protector, the equipment grounding conductor shall be sized not smaller than that given by 250.122(A) using the maximum permitted rating of a dual element time-delay fuse selected for branch-circuit short-circuit and ground-fault protection in accordance with 430.52(C)(1), Exception No. 1.

(E) Flexible Cord and Fixture Wire. The equipment grounding conductor in a flexible cord with the largest circuit conductor 10 AWG or smaller, and the equipment grounding conductor used with fixture wires of any size in accordance with 240.5, shall not be smaller than 18 AWG copper and shall not be smaller than the circuit conductors. The equipment grounding conductor in a flexible cord with a circuit conductor larger than 10 AWG shall be sized in accordance with Table 250.122.

(F) Conductors in Parallel. Where conductors are installed in parallel in multiple raceways or cables as permitted in 310.10(H), the equipment grounding conductors, where used, shall be installed in parallel in each raceway or cable. Where conductors are installed in parallel in the same raceway, cable, or cable tray as permitted in 310.10(H), a single equipment grounding conductor shall be permitted. Equipment grounding conductors installed in cable tray shall meet the minimum requirements of 392.10(B)(1)(c).

Each equipment grounding conductor shall be sized in compliance with 250.122.

(G) Feeder Taps. Equipment grounding conductors run with feeder taps shall not be smaller than shown in Table 250.122 based on the rating of the overcurrent device ahead of the feeder but shall not be required to be larger than the tap conductors.

250.124 Equipment Grounding Conductor Continuity.

(A) Separable Connections. Separable connections such as those provided in drawout equipment or attachment plugs and mating connectors and receptacles shall provide for first-make, last-break of the equipment grounding conductor. First-make, last-break shall not be required where interlocked equipment, plugs, receptacles, and connectors preclude energization without grounding continuity.

(B) Switches. No automatic cutout or switch shall be placed in the equipment grounding conductor of a premises wiring system unless the opening of the cutout or switch disconnects all sources of energy.

250.126 Identification of Wiring Device Terminals. The terminal for the connection of the equipment grounding conductor shall be identified by one of the following:

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Table 250.122 Minimum Size Equipment Grounding Conductors for Grounding Raceway and Equipment
Rating or Setting of Automatic Overcurrent Device in Circuit Ahead of Equipment, Conduit, etc., Not Exceeding (Amperes) Size (AWG or kcmil)
Copper Aluminum or Copper-Clad Aluminum*
  15
  20
  60
 100
 14
 12
 10
  8
 12
 10
  8
  6
 200
 300
 400
  6
  4
  3
  4
  2
  1
 500
 600
 800
   2
   1
 1/0
 1/0
 2/0
 3/0
1000
1200
1600
 2/0
 3/0
 4/0
 4/0
250
350
2000
2500
3000
250
350
400
400
600
600
4000
5000
6000
500
700
800
750
1200
1200
Note: Where necessary to comply with 250.4(A)(5) or (B)(4), the equipment grounding conductor shall be sized larger than given in this table.
* See installation restrictions in 250.120.
  1. A green, not readily removable terminal screw with a hexagonal head.
  2. A green, hexagonal, not readily removable terminal nut.
  3. A green pressure wire connector. If the terminal for the grounding conductor is not visible, the conductor entrance hole shall be marked with the word green or ground, the letters G or GR, a grounding symbol, or otherwise identified by a distinctive green color. If the terminal for the equipment grounding conductor is readily removable, the area adjacent to the terminal shall be similarly marked.

Informational Note: See Informational Note Figure 250.126.

Image

Informational Note Figure 250.126 One Example of a Symbol Used to Identify the Grounding Termination Point for an Equipment Grounding Conductor.

VII. Methods of Equipment Grounding

250.130 Equipment Grounding Conductor Connections. Equipment grounding conductor connections at the source of separately derived systems shall be made in accordance with 250.30(A)(1). Equipment grounding conductor connections at service equipment shall be made as indicated in 250.130(A) or (B). For replacement of non-grounding-type receptacles with grounding-type receptacles and for branch-circuit extensions only in existing installations that do not have an equipment grounding conductor in the branch circuit, connections shall be permitted as indicated in 250.130(C).

(A) For Grounded Systems. The connection shall be made by bonding the equipment grounding conductor to the grounded service conductor and the grounding electrode conductor.

(B) For Ungrounded Systems. The connection shall be made by bonding the equipment grounding conductor to the grounding electrode conductor.

(C) Nongrounding Receptacle Replacement or Branch Circuit Extensions. The equipment grounding conductor of a grounding-type receptacle or a branch-circuit extension shall be permitted to be connected to any of the following:

  1. Any accessible point on the grounding electrode system as described in 250.50
  2. Any accessible point on the grounding electrode conductor
  3. The equipment grounding terminal bar within the enclosure where the branch circuit for the receptacle or branch circuit originates
  4. For grounded systems, the grounded service conductor within the service equipment enclosure
  5. For ungrounded systems, the grounding terminal bar within the service equipment enclosure

Informational Note: See 406.4(D) for the use of a ground-fault circuit-interrupting type of receptacle.

250.132 Short Sections of Raceway. Isolated sections of metal raceway or cable armor, where required to be grounded, shall be connected to an equipment grounding conductor in accordance with 250.134.

250.134 Equipment Fastened in Place or Connected by Permanent Wiring Methods (Fixed) — Grounding. Unless grounded by connection to the grounded circuit conductor as permitted by 250.32, 250.140, and 250.142, non-current-carrying metal parts of equipment, raceways, and other enclosures, if grounded, shall be connected to an equipment grounding conductor by one of the methods specified in 250.134(A) or (B).

70-125

(A) Equipment Grounding Conductor Types. By connecting to any of the equipment grounding conductors permitted by 250.118.

(B) With Circuit Conductors. By connecting to an equipment grounding conductor contained within the same raceway, cable, or otherwise run with the circuit conductors.

Exception No. 1: As provided in 250.130(C), the equipment grounding conductor shall be permitted to be run separately from the circuit conductors.

Exception No. 2: For dc circuits, the equipment grounding conductor shall be permitted to be run separately from the circuit conductors.

Informational Note No. 1: See 250.102 and 250.168 for equipment bonding jumper requirements.

Informational Note No. 2: See 400.7 for use of cords for fixed equipment.

250.136 Equipment Considered Grounded. Under the conditions specified in 250.136(A) and (B), the normally non-current-carrying metal parts of the equipment shall be considered grounded.

(A) Equipment Secured to Grounded Metal Supports. Electrical equipment secured to and in electrical contact with a metal rack or structure provided for its support and connected to an equipment grounding conductor by one of the means indicated in 250.134. The structural metal frame of a building shall not be used as the required equipment grounding conductor for ac equipment.

(B) Metal Car Frames. Metal car frames supported by metal hoisting cables attached to or running over metal sheaves or drums of elevator machines that are connected to an equipment grounding conductor by one of the methods indicated in 250.134.

250.138 Cord-and-Plug-Connected Equipment. Non-current-carrying metal parts of cord-and-plug-connected equipment, if grounded, shall be connected to an equipment grounding conductor by one of the methods in 250.138(A) or (B).

(A) By Means of an Equipment Grounding Conductor. By means of an equipment grounding conductor run with the power supply conductors in a cable assembly or flexible cord properly terminated in a grounding-type attachment plug with one fixed grounding contact.

Exception: The grounding contacting pole of grounding-type plug-in ground-fault circuit interrupters shall be permitted to be of the movable, self-restoring type on circuits operating at not over 150 volts between any two conductors or over 150 volts between any conductor and ground.

(B) By Means of a Separate Flexible Wire or Strap. By means of a separate flexible wire or strap, insulated or bare, connected to an equipment grounding conductor, and protected as well as practicable against physical damage, where part of equipment.

250.140 Frames of Ranges and Clothes Dryers. Frames of electric ranges, wall-mounted ovens, counter-mounted cooking units, clothes dryers, and outlet or junction boxes that are part of the circuit for these appliances shall be connected to the equipment grounding conductor in the manner specified by 250.134 or 250.138.

Exception: For existing branch-circuit installations only where an equipment grounding conductor is not present in the outlet or junction box, the frames of electric ranges, wall-mounted ovens, counter-mounted cooking units, clothes dryers, and outlet or junction boxes that are part of the circuit for these appliances shall be permitted to be connected to the grounded circuit conductor if all the following conditions are met.

  1. The supply circuit is 120/240-volt, single-phase, 3-wire; or 208Y/120-volt derived from a 3-phase, 4-wire, wye-connected system.
  2. The grounded conductor is not smaller than 10 AWG copper or 8 AWG aluminum.
  3. The grounded conductor is insulated, or the grounded conductor is uninsulated and part of a Type SE service-entrance cable and the branch circuit originates at the service equipment,
  4. Grounding contacts of receptacles furnished as part of the equipment are bonded to the equipment.

250.142 Use of Grounded Circuit Conductor for Grounding Equipment.

(A) Supply-Side Equipment. A grounded circuit conductor shall be permitted to ground non-current-carrying metal parts of equipment, raceways, and other enclosures at any of the following locations:

  1. On the supply side or within the enclosure of the ac service-disconnecting means
  2. On the supply side or within the enclosure of the main disconnecting means for separate buildings as provided in 250.32(B)
  3. On the supply side or within the enclosure of the main disconnecting means or overcurrent devices of a separately derived system where permitted by 250.30(A)(1)

(B) Load-Side Equipment. Except as permitted in 250.30(A)(1) and 250.32(B) Exception, a grounded circuit conductor shall not be used for grounding non-current-carrying metal parts of equipment on the load side of the service disconnecting means or on the load

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side of a separately derived system disconnecting means or the overcurrent devices for a separately derived system not having a main disconnecting means.

Exception No. 1: The frames of ranges, wall-mounted ovens, counter-mounted cooking units, and clothes dryers under the conditions permitted for existing installations by 250.140 shall be permitted to be connected to the grounded circuit conductor.

Exception No. 2: It shall be permissible to ground meter enclosures by connection to the grounded circuit conductor on the load side of the service disconnect where all of the following conditions apply:

  1. No service ground-fault protection is installed.
  2. All meter enclosures are located immediately adjacent to the service disconnecting means.
  3. The size of the grounded circuit conductor is not smaller than the size specified in Table 250.122 for equipment grounding conductors.

Exception No. 3: Direct-current systems shall be permitted to be grounded on the load side of the disconnecting means or overcurrent device in accordance with 250.164.

Exception No. 4: Electrode-type boilers operating at over 600 volts shall be grounded as required in 490.72(E)(1) and 490.74.

250.144 Multiple Circuit Connections. Where equipment is grounded and is supplied by separate connection to more than one circuit or grounded premises wiring system, an equipment grounding conductor termination shall be provided for each such connection as specified in 250.134 and 250.138.

250.146 Connecting Receptacle Grounding Terminal to Box. An equipment bonding jumper shall be used to connect the grounding terminal of a grounding-type receptacle to a grounded box unless grounded as in 250.146(A) through (D). The equipment bonding jumper shall be sized in accordance with Table 250.122 based on the rating of the overcurrent device protecting the circuit conductors.

(A) Surface-Mounted Box. Where the box is mounted on the surface, direct metal-to-metal contact between the device yoke and the box or a contact yoke or device that complies with 250.146(B) shall be permitted to ground the receptacle to the box. At least one of the insulating washers shall be removed from receptacles that do not have a contact yoke or device that complies with 250.146(B) to ensure direct metal-to-metal contact. This provision shall not apply to cover-mounted receptacles unless the box and cover combination are listed as providing satisfactory ground continuity between the box and the receptacle. A listed exposed work cover shall be permitted to be the grounding and bonding means when (1) the device is attached to the cover with at least two fasteners that are permanent (such as a rivet) or have a thread locking or screw or nut locking means and (2) when the cover mounting holes are located on a flat non-raised portion of the cover.

(B) Contact Devices or Yokes. Contact devices or yokes designed and listed as self-grounding shall be permitted in conjunction with the supporting screws to establish the grounding circuit between the device yoke and flush-type boxes.

(C) Floor Boxes. Floor boxes designed for and listed as providing satisfactory ground continuity between the box and the device shall be permitted.

(D) Isolated Receptacles. Where installed for the reduction of electrical noise (electromagnetic interference) on the grounding circuit, a receptacle in which the grounding terminal is purposely insulated from the receptacle mounting means shall be permitted. The receptacle grounding terminal shall be connected to an insulated equipment grounding conductor run with the circuit conductors. This equipment grounding conductor shall be permitted to pass through one or more panelboards without a connection to the panel-board grounding terminal bar as permitted in 408.40, Exception, so as to terminate within the same building or structure directly at an equipment grounding conductor terminal of the applicable derived system or service. Where installed in accordance with the provisions of this section, this equipment grounding conductor shall also be permitted to pass through boxes, wireways, or other enclosures without being connected to such enclosures.

Informational Note: Use of an isolated equipment grounding conductor does not relieve the requirement for grounding the raceway system and outlet box.

250.148 Continuity and Attachment of Equipment Grounding Conductors to Boxes. Where circuit conductors are spliced within a box, or terminated on equipment within or supported by a box, any equipment grounding conductor(s) associated with those circuit conductors shall be connected within the box or to the box with devices suitable for the use in accordance with 250.148(A) through (E).

Exception: The equipment grounding conductor permitted in 250.146(D) shall not be required to be connected to the other equipment grounding conductors or to the box.

(A) Connections. Connections and splices shall be made in accordance with 110.14(B) except that insulation shall not be required.

(B) Grounding Continuity. The arrangement of grounding connections shall be such that the disconnection or the removal of a receptacle, luminaire, or other device fed from the box does not interfere with or interrupt the grounding continuity.

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(C) Metal Boxes. A connection shall be made between the one or more equipment grounding conductors and a metal box by means of a grounding screw that shall be used for no other purpose, equipment listed for grounding, or a listed grounding device.

(D) Nonmetallic Boxes. One or more equipment grounding conductors brought into a nonmetallic outlet box shall be arranged such that a connection can be made to any fitting or device in that box requiring grounding.

(E) Solder. Connections depending solely on solder shall not be used.

VIII. Direct-Current Systems

250.160 General. Direct-current systems shall comply with Part VIII and other sections of Article 250 not specifically intended for ac systems.

250.162 Direct-Current Circuits and Systems to Be Grounded. Direct-current circuits and systems shall be grounded as provided for in 250.162(A) and (B).

(A) Two-Wire, Direct-Current Systems. A 2-wire, dc system supplying premises wiring and operating at greater than 50 volts but not greater than 300 volts shall be grounded.

Exception No. 1: A system equipped with a ground detector and supplying only industrial equipment in limited areas shall not be required to be grounded.

Exception No. 2: A rectifier-derived dc system supplied from an ac system complying with 250.20 shall not be required to be grounded.

Exception No. 3: Direct-current fire alarm circuits having a maximum current of 0.030 ampere as specified in Article 760, Part III, shall not be required to be grounded.

(B) Three-Wire, Direct-Current Systems. The neutral conductor of all 3-wire, dc systems supplying premises wiring shall be grounded.

250.164 Point of Connection for Direct-Current Systems.

(A) Off-Premises Source. Direct-current systems to be grounded and supplied from an off-premises source shall have the grounding connection made at one or more supply stations. A grounding connection shall not be made at individual services or at any point on the premises wiring.

(B) On-Premises Source. Where the dc system source is located on the premises, a grounding connection shall be made at one of the following:

  1. The source
  2. The first system disconnection means or overcurrent device
  3. By other means that accomplish equivalent system protection and that utilize equipment listed and identified for the use

250.166 Size of the Direct-Current Grounding Electrode Conductor. The size of the grounding electrode conductor for a dc system shall be as specified in 250.166(A) and (B), except as permitted by 250.166(C) through (E).

(A) Not Smaller Than the Neutral Conductor. Where the dc system consists of a 3-wire balancer set or a balancer winding with overcurrent protection as provided in 445.12(D), the grounding electrode conductor shall not be smaller than the neutral conductor and not smaller than 8 AWG copper or 6 AWG aluminum.

(B) Not Smaller Than the Largest Conductor. Where the dc system is other than as in 250.166(A), the grounding electrode conductor shall not be smaller than the largest conductor supplied by the system, and not smaller than 8 AWG copper or 6 AWG aluminum.

(C) Connected to Rod, Pipe, or Plate Electrodes. Where connected to rod, pipe, or plate electrodes as in 250.52(A)(5) or (A)(7), that portion of the grounding electrode conductor that is the sole connection to the grounding electrode shall not be required to be larger than 6 AWG copper wire or 4 AWG aluminum wire.

(D) Connected to a Concrete-Encased Electrode. Where connected to a concrete-encased electrode as in 250.52(A)(3), that portion of the grounding electrode conductor that is the sole connection to the grounding electrode shall not be required to be larger than 4 AWG copper wire.

(E) Connected to a Ground Ring. Where connected to a ground ring as in 250.52(A)(4), that portion of the grounding electrode conductor that is the sole connection to the grounding electrode shall not be required to be larger than the conductor used for the ground ring.

250.168 Direct-Current System Bonding Jumper. For direct-current systems that are to be grounded, an unspliced bonding jumper shall be used to connect the equipment grounding conductor(s) to the grounded conductor at the source or the first system disconnecting means where the system is grounded. The size of the bonding jumper shall not be smaller than the system grounding electrode conductor specified in 250.166 and shall comply with the provisions of 250.28(A), (B), and (C).

250.169 Ungrounded Direct-Current Separately Derived Systems. Except as otherwise permitted in 250.34 for portable and vehicle-mounted generators, an ungrounded dc separately derived system supplied from a stand-alone power source (such as an engine-generator set) shall have a

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grounding electrode conductor connected to an electrode that complies with Part III of this article to provide for grounding of metal enclosures, raceways, cables, and exposed non-current-carrying metal parts of equipment. The grounding electrode conductor connection shall be to the metal enclosure at any point on the separately derived system from the source to the first system disconnecting means or overcurrent device, or it shall be made at the source of a separately derived system that has no disconnecting means or overcurrent devices.

The size of the grounding electrode conductor shall be in accordance with 250.166.

IX. Instruments, Meters, and Relays

250.170 Instrument Transformer Circuits. Secondary circuits of current and potential instrument transformers shall be grounded where the primary windings are connected to circuits of 300 volts or more to ground and, where on switchboards, shall be grounded irrespective of voltage.

Exception No. 1: Circuits where the primary windings are connected to circuits of less than 1000 volts with no live parts or wiring exposed or accessible to other than qualified persons.

Exception No. 2: Current transformer secondaries connected in a three-phase delta configuration shall not be required to be grounded.

250.172 Instrument Transformer Cases. Cases or frames of instrument transformers shall be connected to the equipment grounding conductor where accessible to other than qualified persons.

Exception: Cases or frames of current transformers, the primaries of which are not over 150 volts to ground and that are used exclusively to supply current to meters.

250.174 Cases of Instruments, Meters, and Relays Operating at Less Than 1000 Volts. Instruments, meters, and relays operating with windings or working parts at less than 1000 volts shall be connected to the equipment grounding conductor as specified in 250.174(A), (B), or (C).

(A) Not on Switchboards. Instruments, meters, and relays not located on switchboards, operating with windings or working parts at 300 volts or more to ground, and accessible to other than qualified persons, shall have the cases and other exposed metal parts connected to the equipment grounding conductor.

(B) On Dead-Front Switchboards. Instruments, meters, and relays (whether operated from current and potential transformers or connected directly in the circuit) on switchboards having no live parts on the front of the panels shall have the cases connected to the equipment grounding conductor.

(C) On Live-Front Switchboards. Instruments, meters, and relays (whether operated from current and potential transformers or connected directly in the circuit) on switchboards having exposed live parts on the front of panels shall not have their cases connected to the equipment grounding conductor. Mats of insulating rubber or other suitable floor insulation shall be provided for the operator where the voltage to ground exceeds 150.

250.176 Cases of Instruments, Meters, and Relays — Operating Voltage 1 kV and Over. Where instruments, meters, and relays have current-carrying parts of 1 kV and over to ground, they shall be isolated by elevation or protected by suitable barriers, grounded metal, or insulating covers or guards. Their cases shall not be connected to the equipment grounding conductor.

Exception: Cases of electrostatic ground detectors where the internal ground segments of the instrument are connected to the instrument case and grounded and the ground detector is isolated by elevation.

250.178 Instrument Equipment Grounding Conductor. The equipment grounding conductor for secondary circuits of instrument transformers and for instrument cases shall not be smaller than 12 AWG copper or 10 AWG aluminum. Cases of instrument transformers, instruments, meters, and relays that are mounted directly on grounded metal surfaces of enclosures or grounded metal switchboard panels shall be considered to be grounded, and no additional equipment grounding conductor shall be required.

X. Grounding of Systems and Circuits of over 1 kV

250.180 General. Where systems over 1 kV are grounded, they shall comply with all applicable provisions of the preceding sections of this article and with 250.182 through 250.190, which supplement and modify the preceding sections.

250.182 Derived Neutral Systems. A system neutral point derived from a grounding transformer shall be permitted to be used for grounding systems over 1 kV.

250.184 Solidly Grounded Neutral Systems. Solidly grounded neutral systems shall be permitted to be either single point grounded or multigrounded neutral.

(A) Neutral Conductor.

(1) Insulation Level. The minimum insulation level for neutral conductors of solidly grounded systems shall be 600 volts.

Exception No. 1: Bare copper conductors shall be permitted to be used for the neutral conductor of the following:

  1. Service-entrance conductors
  2. Service laterals
  3. Direct-buried portions of feeders.
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Exception No. 2: Bare conductors shall be permitted for the neutral conductor of overhead portions installed outdoors.

Exception No. 3: The grounded neutral conductor shall be permitted to be a bare conductor if isolated from phase conductors and protected from physical damage.

Informational Note: See 225.4 for conductor covering where within 3.0 m (10 ft) of any building or other structure.

(2) Ampacity. The neutral conductor shall be of sufficient ampacity for the load imposed on the conductor but not less than 33 ⅓ percent of the ampacity of the phase conductors.

Exception: In industrial and commercial premises under engineering supervision, it shall be permissible to size the ampacity of the neutral conductor to not less than 20 percent of the ampacity of the phase conductor.

(B) Single-Point Grounded Neutral System. Where a single-point grounded neutral system is used, the following shall apply:

  1. A single-point grounded neutral system shall be permitted to be supplied from (a) or (b):
    1. A separately derived system
    2. A multigrounded neutral system with an equipment grounding conductor connected to the multi-grounded neutral conductor at the source of the single-point grounded neutral system
  2. A grounding electrode shall be provided for the system.
  3. A grounding electrode conductor shall connect the grounding electrode to the system neutral conductor.
  4. A bonding jumper shall connect the equipment grounding conductor to the grounding electrode conductor.
  5. An equipment grounding conductor shall be provided to each building, structure, and equipment enclosure.
  6. A neutral conductor shall only be required where phase-to-neutral loads are supplied.
  7. The neutral conductor, where provided, shall be insulated and isolated from earth except at one location.
  8. An equipment grounding conductor shall be run with the phase conductors and shall comply with (a), (b), and (c):
    1. Shall not carry continuous load
    2. May be bare or insulated
    3. Shall have sufficient ampacity for fault current duty

(C) Multigrounded Neutral Systems. Where a multi-grounded neutral system is used, the following shall apply:

  1. The neutral conductor of a solidly grounded neutral system shall be permitted to be grounded at more than one point. Grounding shall be permitted at one or more of the following locations:
    1. Transformers supplying conductors to a building or other structure
    2. Underground circuits where the neutral conductor is exposed
    3. Overhead circuits installed outdoors
  2. The multigrounded neutral conductor shall be grounded at each transformer and at other additional locations by connection to a grounding electrode.
  3. At least one grounding electrode shall be installed and connected to the multigrounded neutral conductor every 400 m (1300 ft).
  4. The maximum distance between any two adjacent electrodes shall not be more than 400 m (1300 ft).
  5. In a multigrounded shielded cable system, the shielding shall be grounded at each cable joint that is exposed to personnel contact.

250.186 Impedance Grounded Neutral Systems. Impedance grounded neutral systems in which a grounding impedance, usually a resistor, limits the ground-fault current shall be permitted where all of the following conditions are met:

  1. The conditions of maintenance and supervision ensure that only qualified persons service the installation.
  2. Ground detectors are installed on the system.
  3. Line-to-neutral loads are not served.

Impedance grounded neutral systems shall comply with the provisions of 250.186(A) through (D).

(A) Location. The grounding impedance shall be inserted in the grounding electrode conductor between the grounding electrode of the supply system and the neutral point of the supply transformer or generator.

(B) Identified and Insulated. The neutral conductor of an impedance grounded neutral system shall be identified, as well as fully insulated with the same insulation as the phase conductors.

(C) System Neutral Conductor Connection. The system neutral conductor shall not be connected to ground, except through the neutral grounding impedance.

(D) Equipment Grounding Conductors. Equipment grounding conductors shall be permitted to be bare and shall be electrically connected to the ground bus and grounding electrode conductor.

250.188 Grounding of Systems Supplying Portable or Mobile Equipment. Systems supplying portable or mobile equipment over 1 kV, other than substations installed on a temporary basis, shall comply with 250.188(A) through (F).

(A) Portable or Mobile Equipment. Portable or mobile equipment over 1 kV shall be supplied from a system having

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its neutral conductor grounded through an impedance. Where a delta-connected system over 1 kV is used to supply portable or mobile equipment, a system neutral point and associated neutral conductor shall be derived.

(B) Exposed Non-Current-Carrying Metal Parts. Exposed non-current-carrying metal parts of portable or mobile equipment shall be connected by an equipment grounding conductor to the point at which the system neutral impedance is grounded.

(C) Ground-Fault Current. The voltage developed between the portable or mobile equipment frame and ground by the flow of maximum ground-fault current shall not exceed 100 volts.

(D) Ground-Fault Detection and Relaying. Ground-fault detection and relaying shall be provided to automatically de-energize any component of a system over 1 kV that has developed a ground fault. The continuity of the equipment grounding conductor shall be continuously monitored so as to de-energize automatically the circuit of the system over 1 kV to the portable or mobile equipment upon loss of continuity of the equipment grounding conductor.

(E) Isolation. The grounding electrode to which the portable or mobile equipment system neutral impedance is connected shall be isolated from and separated in the ground by at least 6.0 m (20 ft) from any other system or equipment grounding electrode, and there shall be no direct connection between the grounding electrodes, such as buried pipe and fence, and so forth.

(F) Trailing Cable and Couplers. Trailing cable and couplers of systems over 1 kV for interconnection of portable or mobile equipment shall meet the requirements of Part III of Article 400 for cables and 490.55 for couplers.

250.190 Grounding of Equipment.

(A) Equipment Grounding. All non-current-carrying metal parts of fixed, portable, and mobile equipment and associated fences, housings, enclosures, and supporting structures shall be grounded.

Exception: Where isolated from ground and located such that any person in contact with ground cannot contact such metal parts when the equipment is energized, the metal parts shall not he required to be grounded.

Informational Note: See 250.110, Exception No. 2, for pole-mounted distribution apparatus.

(B) Grounding Electrode Conductor. If a grounding electrode conductor connects non-current-carrying metal parts to ground, the grounding electrode conductor shall be sized in accordance with Table 250.66, based on the size of the largest ungrounded service, feeder, or branch-circuit conductors supplying the equipment. The grounding electrode conductor shall not be smaller than 6 AWG copper or 4 AWG aluminum.

(C) Equipment Grounding Conductor. Equipment grounding conductors shall comply with 250.190(C)(1) through (C)(3).

(1) General. Equipment grounding conductors that are not an integral part of a cable assembly shall not be smaller than 6 AWG copper or 4 AWG aluminum.

(2) Shielded Cables. The metallic insulation shield encircling the current carrying conductors shall be permitted to be used as an equipment grounding conductor, if it is rated for clearing time of ground fault current protective device operation without damaging the metallic shield. The metallic tape insulation shield and drain wire insulation shield shall not be used as an equipment grounding conductor for solidly grounded systems.

(3) Sizing. Equipment grounding conductors shall be sized in accordance with Table 250.122 based on the current rating of the fuse or the overcurrent setting of the protective relay.

Informational Note: The overcurrent rating for a circuit breaker is the combination of the current transformer ratio and the current pickup setting of the protective relay.

250.191 Grounding System at Alternating-Current Substations. For ac substations, the grounding system shall be in accordance with Part III of Article 250.

Informational Note: For further information on outdoor ac substation grounding, see ANSI/IEEE 80-2000, IEEE Guide for Safely in AC Substation Grounding.

ARTICLE 280
Surge Arresters, Over 1 kV

I. General

280.1 Scope. This article covers general requirements, installation requirements, and connection requirements for surge arresters installed on premises wiring systems over 1 kV.

280.2 Uses Not Permitted. A surge arrester shall not be installed where the rating of the surge arrester is less than the maximum continuous phase-to-ground power frequency voltage available at the point of application.

280.3 Number Required. Where used at a point on a circuit, a surge arrester shall be connected to each ungrounded conductor. A single installation of such surge arresters shall

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be permitted to protect a number of interconnected circuits, provided that no circuit is exposed to surges while disconnected from the surge arresters.

280.4 Surge Arrester Selection. The surge arresters shall comply with 280.4(A) and (B).

(A) Rating. The rating of a surge arrester shall be equal to or greater than the maximum continuous operating voltage available at the point of application.

(1) Solidly Grounded Systems. The maximum continuous operating voltage shall be the phase-to-ground voltage of the system.

(2) Impedance or Ungrounded System. The maximum continuous operating voltage shall be the phase-to-phase voltage of the system.

(B) Silicon Carbide Types. The rating of a silicon carbide-type surge arrester shall be not less than 125 percent of the rating specified in 280.4(A).

Informational Note No. 1: For further information on surge arresters, see ANSI/IEEE C62.11-2005, Standard for Metal-Oxide Surge Arresters for Alternating-Current Power Circuits (>1 kV); and ANSI/IEEE C62.22-1997, Guide for the Application of Metal-Oxide Surge Arresters for Alternating-Current Systems.

Informational Note No. 2: The selection of a properly rated metal oxide arrester is based on considerations of maximum continuous operating voltage and the magnitude and duration of overvoltages at the arrester location as affected by phase-to-ground faults, system grounding techniques, switching surges, and other causes. See the manufacturer’s application rules for selection of the specific arrester to be used at a particular location.

II. Installation

280.11 Location. Surge arresters shall be permitted to be located indoors or outdoors. Surge arresters shall be made inaccessible to unqualified persons, unless listed for installation in accessible locations.

280.12 Routing of Surge Arrester Grounding Conductors. The conductor used to connect the surge arrester to line, bus, or equipment and to a grounding conductor connection point as provided in 280.21 shall not be any longer than necessary and shall avoid unnecessary bends.

III. Connecting Surge Arresters

280.21 Connection. The arrester shall be connected to one of the following:

  1. Grounded service conductor
  2. Grounding electrode conductor
  3. Grounding electrode for the service
  4. Equipment grounding terminal in the service equipment

280.23 Surge-Arrester Conductors. The conductor between the surge arrester and the line and the surge arrester and the grounding connection shall not be smaller than 6 AWG copper or aluminum.

280.24 Interconnections. The surge arrester protecting a transformer that supplies a secondary distribution system shall be interconnected as specified in 280.24(A), (B), or (C).

(A) Metallic Interconnections. A metallic interconnection shall be made to the secondary grounded circuit conductor or the secondary circuit grounding electrode conductor provided that, in addition to the direct grounding connection at the surge arrester, the following occurs:

(1) Additional Grounding Connection. The grounded conductor of the secondary has elsewhere a grounding connection to a continuous metal underground water piping system. In urban water-pipe areas where there are at least four water-pipe connections on the neutral conductor and not fewer than four such connections in each mile of neutral conductor, the metallic interconnection shall be permitted to be made to the secondary neutral conductor with omission of the direct grounding connection at the surge arrester.

(2) Multigrounded Neutral System Connection. The grounded conductor of the secondary system is a part of a multigrounded neutral system or static wire of which the primary neutral conductor or static wire has at least four grounding connections in each mile of line in addition to a grounding connection at each service.

(B) Through Spark Gap or Device. Where the surge arrester grounding electrode conductor is not connected as in 280.24(A), or where the secondary is not grounded as in 280.24(A) but is otherwise grounded as in 250.52, an interconnection shall be made through a spark gap or listed device as required by 280.24(B)(1) or (B)(2).

(1) Ungrounded or Unigrounded Primary System. For ungrounded or unigrounded primary systems, the spark gap or listed device shall have a 60-Hz breakdown voltage of at least twice the primary circuit voltage but not necessarily more than 10 kV, and there shall be at least one other ground on the grounded conductor of the secondary that is not less than 6.0 m (20 ft) distant from the surge-arrester grounding electrode.

(2) Multigrounded Neutral Primary System. For multigrounded neutral primary systems, the spark gap or listed device shall have a 60-Hz breakdown of not more than 3 kV, and there shall be at least one other ground on the grounded conductor

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of the secondary that is not less than 6.0 m (20 ft) distant from the surge-arrester grounding electrode.

(C) By Special Permission. An interconnection of the surge-arrester ground and the secondary neutral conductor, other than as provided in 280.24(A) or (B) shall be permitted to be made only by special permission.

280.25 Grounding Electrode Conductor Connections and Enclosures. Except as indicated in this article, surge-arrester grounding electrode conductor connections shall be made as specified in Article 250, Parts III and X. Grounding electrode conductors installed in metal enclosures shall comply with 250.64(E).

ARTICLE 285
Surge-Protective Devices (SPDs),
1 kV or Less

I. General

285.1 Scope. This article covers general requirements, installation requirements, and connection requirements for SPDs [surge arresters and transient voltage surge suppressors (TVSSs)] permanently installed on premises wiring systems 1 kV or less.

Informational Note No. 1: Surge arresters less than 1 kV are also known as Type 1 SPDs.

Informational Note No. 2: Transient voltage surge suppressors (TVSSs) are also known as Type 2 and Type 3 SPDs.

285.3 Uses Not Permitted. An SPD (surge arrester or TVSS) device shall not be installed in the following:

  1. Circuits exceeding 1 kV
  2. On ungrounded systems, impedance grounded systems, or corner grounded delta systems unless listed specifically for use on these systems.
  3. Where the rating of the SPD (surge arrester or TVSS) is less than the maximum continuous phase-to-ground power frequency voltage available at the point of application

Informational Note: For further information on SPDs (TVSSs), see NEMA LS 1-1992, Standard for Low Voltage Surge Suppression Devices. The selection of a properly rated SPD (TVSS) is based on criteria such as maximum continuous operating voltage, the magnitude and duration of overvoltages at the suppressor location as affected by phase-to-ground faults, system grounding techniques, and switching surges.

285.4 Number Required. Where used at a point on a circuit, the SPD (surge arrester or TVSS) shall be connected to each ungrounded conductor.

285.5 Listing. An SPD (surge arrester or TVSS) shall be a listed device.

285.6 Short-Circuit Current Rating. The SPD (surge arrester or TVSS) shall be marked with a short-circuit current rating and shall not be installed at a point on the system where the available fault current is in excess of that rating. This marking requirement shall not apply to receptacles.

II. Installation

285.11 Location. SPDs (surge arresters or TVSSs) shall be permitted to be located indoors or outdoors and shall be made inaccessible to unqualified persons, unless listed for installation in accessible locations.

285.12 Routing of Connections. The conductors used to connect the SPD (surge arrester or TVSS) to the line or bus and to ground shall not be any longer than necessary and shall avoid unnecessary bends.

III. Connecting SPDs

285.21 Connection. Where an SPD (surge arrester or TVSS) device is installed, it shall comply with 285.23 through 285.28.

285.23 Type 1 SPDs (Surge Arresters). Type 1 SPDs shall be installed in accordance with 285.23(A) and (B).

(A) Installation. Type 1 SPDs (surge arresters) shall be installed as follows:

  1. Type 1 SPDs (surge arresters) shall be permitted to be connected to the supply side of the service disconnect as permitted in 230.82(4) or
  2. Type 1 SPDs (surge arresters) shall be permitted to be connected as specified in 285.24.

(B) At the Service. When installed at services, Type 1 SPDs shall be connected to one of the following:

  1. Grounded service conductor
  2. Grounding electrode conductor
  3. Grounding electrode for the service
  4. Equipment grounding terminal in the service equipment

285.24 Type 2 SPDs (TVSSs). Type 2 SPDs (TVSSs) shall be installed in accordance with 285.24(A) through (C).

(A) Service-Supplied Building or Structure. Type 2 SPDs (TVSSs) shall be connected anywhere on the load

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side of a service disconnect overcurrent device required in 230.91, unless installed in accordance with 230.82(8).

(B) Feeder-Supplied Building or Structure. Type 2 SPDs (TVSSs) shall be connected at the building or structure anywhere on the load side of the first overcurrent device at the building or structure.

(C) Separately Derived System. The SPD (TVSS) shall be connected on the load side of the first overcurrent device in a separately derived system.

285.25 Type 3 SPDs. Type 3 SPDs (TVSSs) shall be permitted to be installed on the load side of branch-circuit overcurrent protection up to the equipment served. If included in the manufacturer’s instructions, the Type 3 SPD connection shall be a minimum 10 m (30 ft) of conductor distance from the service or separately derived system disconnect.

285.26 Conductor Size. Line and grounding conductors shall not be smaller than 14 AWG copper or 12 AWG aluminum.

285.27 Connection Between Conductors. An SPD (surge arrester or TVSS) shall be permitted to be connected between any two conductors — ungrounded conductor(s), grounded conductor, equipment grounding conductor, or grounding electrode conductor. The grounded conductor and the equipment grounding conductor shall be interconnected only by the normal operation of the SPD (surge arrester or TVSS) during a surge.

285.28 Grounding Electrode Conductor Connections and Enclosures. Except as indicated in this article, SPD grounding connections shall be made as specified in Article 250, Part III. Grounding electrode conductors installed in metal enclosures shall comply with 250.64(E).

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Chapter 3 Wiring Methods and Materials

ARTICLE 300
Wiring Methods

I. General Requirements

300.1 Scope.

(A) All Wiring Installations. This article covers wiring methods for all wiring installations unless modified by other articles.

(B) Integral Parts of Equipment. The provisions of this article are not intended to apply to the conductors that form an integral part of equipment, such as motors, controllers, motor control centers, or factory assembled control equipment or listed utilization equipment.

(C) Metric Designators and Trade Sizes. Metric designators and trade sizes for conduit, tubing, and associated fittings and accessories shall be as designated in Table 300.1(C).

Table 300.1(C) Metric Designators and Trade Sizes
Metric Designator Trade Size
  12   3/8
  16   ½
  21   ¾
  27 1
  35
  41
  53 2
  63
  78 3
  91
103 4
129 5
155 6
Note: The metric designators and trade sizes are for identification purposes only and are not actual dimensions.

300.2 Limitations.

(A) Voltage. Wiring methods specified in Chapter 3 shall be used for 600 volts, nominal, or less where not specifically limited in some section of Chapter 3. They shall be permitted for over 600 volts, nominal, where specifically permitted elsewhere in this Code.

(B) Temperature. Temperature limitation of conductors shall be in accordance with 310.15(A)(3).

300.3 Conductors.

(A) Single Conductors. Single conductors specified in Table 310.104(A) shall only be installed where part of a recognized wiring method of Chapter 3.

Exception: Individual conductors shall be permitted where installed as separate overhead conductors in accordance with 225.6.

(B) Conductors of the Same Circuit. All conductors of the same circuit and, where used, the grounded conductor and all equipment grounding conductors and bonding conductors shall be contained within the same raceway, auxiliary gutter, cable tray, cablebus assembly, trench, cable, or cord, unless otherwise permitted in accordance with 300.3(B)(1) through (B)(4).

(1) Paralleled Installations. Conductors shall be permitted to be run in parallel in accordance with the provisions of 310.10(H). The requirement to run all circuit conductors within the same raceway, auxiliary gutter, cable tray, trench, cable, or cord shall apply separately to each portion of the paralleled installation, and the equipment grounding conductors shall comply with the provisions of 250.122. Parallel runs in cable tray shall comply with the provisions of 392.20(C).

Exception: Conductors installed in nonmetallic raceways run underground shall be permitted to be arranged as isolated phase installations. The raceways shall be installed in close proximity, and the conductors shall comply with the provisions of 300.20(B).

(2) Grounding and Bonding Conductors. Equipment grounding conductors shall be permitted to be installed outside a raceway or cable assembly where in accordance with the provisions of 250.130(C) for certain existing installations or in accordance with 250.134(B), Exception No. 2, for dc circuits. Equipment bonding conductors shall be permitted to be installed on the outside of raceways in accordance with 250.102(E).

(3) Nonferrous Wiring Methods. Conductors in wiring methods with a nonmetallic or other nonmagnetic sheath, where run in different raceways, auxiliary gutters, cable trays, trenches, cables, or cords, shall comply with the provisions of 300.20(B). Conductors in single-conductor Type MI cable with a nonmagnetic sheath shall comply with the provisions of 332.31. Conductors of single-conductor Type MC cable with a nonmagnetic sheath shall comply with the provisions of 330.31, 330.116, and 300.20(B).

(4) Enclosures. Where an auxiliary gutter runs between a column-width panelboard and a pull box, and the pull box

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includes neutral terminations, the neutral conductors of circuits supplied from the panelboard shall be permitted to originate in the pull box.

(C) Conductors of Different Systems.

(1) 600 Volts, Nominal, or Less. Conductors of ac and dc circuits, rated 600 volts, nominal, or less, shall be permitted to occupy the same equipment wiring enclosure, cable, or raceway. All conductors shall have an insulation rating equal to at least the maximum circuit voltage applied to any conductor within the enclosure, cable, or raceway.

Informational Note No. 1: See 725.136(A) for Class 2 and Class 3 circuit conductors.

Informational Note No. 2: See 690.4(B) for photovoltaic source and output circuits.

(2) Over 600 Volts, Nominal. Conductors of circuits rated over 600 volts, nominal, shall not occupy the same equipment wiring enclosure, cable, or raceway with conductors of circuits rated 600 volts, nominal, or less unless otherwise permitted in (C)(2)(a) through (C)(2)(e).

(a) Secondary wiring to electric-discharge lamps of 1000 volts or less, if insulated for the secondary voltage involved, shall be permitted to occupy the same luminaire, sign, or outline lighting enclosure as the branch-circuit conductors.

(b) Primary leads of electric-discharge lamp ballasts insulated for the primary voltage of the ballast, where contained within the individual wiring enclosure, shall be permitted to occupy the same luminaire, sign, or outline lighting enclosure as the branch-circuit conductors.

(c) Excitation, control, relay, and ammeter conductors used in connection with any individual motor or starter shall be permitted to occupy the same enclosure as the motor-circuit conductors.

(d) In motors, switchgear and control assemblies, and similar equipment, conductors of different voltage ratings shall be permitted.

(e) In manholes, if the conductors of each system are permanently and effectively separated from the conductors of the other systems and securely fastened to racks, insulators, or other approved supports, conductors of different voltage ratings shall be permitted.

Conductors having nonshielded insulation and operating at different voltage levels shall not occupy the same enclosure, cable, or raceway.

300.4 Protection Against Physical Damage. Where subject to physical damage, conductors, raceways, and cables shall be protected.

(A) Cables and Raceways Through Wood Members.

(1) Bored Holes. In both exposed and concealed locations, where a cable- or raceway-type wiring method is installed through bored holes in joists, rafters, or wood members, holes shall be bored so that the edge of the hole is not less than 32 mm (1¼ in.) from the nearest edge of the wood member. Where this distance cannot be maintained, the cable or raceway shall be protected from penetration by screws or nails by a steel plate(s) or bushing(s), at least 1.6 mm (1/16 in.) thick, and of appropriate length and width installed to cover the area of the wiring.

Exception No. 1: Steel plates shall not be required to protect rigid metal conduit, intermediate metal conduit, rigid nonmetallic conduit, or electrical metallic tubing.

Exception No. 2: A listed and marked steel plate less than 1.6 mm (1/16 in.) thick that provides equal or better protection against nail or screw penetration shall be permitted.

(2) Notches in Wood. Where there is no objection because of weakening the building structure, in both exposed and concealed locations, cables or raceways shall be permitted to be laid in notches in wood studs, joists, rafters, or other wood members where the cable or raceway at those points is protected against nails or screws by a steel plate at least 1.6 mm (1/16 in.) thick, and of appropriate length and width, installed to cover the area of the wiring. The steel plate shall be installed before the building finish is applied.

Exception No. 1: Steel plates shall not be required to protect rigid metal conduit, intermediate meted conduit, rigid nonmetallic conduit, or electrical metallic tubing.

Exception No. 2: A listed and marked steel plate less than 1.6 mm (1/16 in.) thick that provides equal or better protection against nail or screw penetration shall be permitted.

(B) Nonmetallic-Sheathed Cables and Electrical Nonmetallic Tubing Through Metal Framing Members.

(1) Nonmetallic-Sheathed Cable. In both exposed and concealed locations where nonmetallic-sheathed cables pass through either factory- or field-punched, cut, or drilled slots or holes in metal members, the cable shall be protected by listed bushings or listed grommets covering all metal edges that are securely fastened in the opening prior to installation of the cable.

(2) Nonmetallic-Sheathed Cable and Electrical Nonmetallic Tubing. Where nails or screws are likely to penetrate nonmetallic-sheathed cable or electrical nonmetallic tubing, a steel sleeve, steel plate, or steel clip not less than 1.6 mm (1/16 in.) in thickness shall be used to protect the cable or tubing.

Exception: A listed and marked steel plate less than 1.6 mm (1/16 in.) thick that provides equal or better protection against nail or screw penetration shall be permitted.

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(C) Cables Through Spaces Behind Panels Designed to Allow Access. Cables or raceway-type wiring methods, installed behind panels designed to allow access, shall be supported according to their applicable articles.

(D) Cables and Raceways Parallel to Framing Members and Furring Strips. In both exposed and concealed locations, where a cable- or raceway-type wiring method is installed parallel to framing members, such as joists, rafters, or studs, or is installed parallel to furring strips, the cable or raceway shall be installed and supported so that the nearest outside surface of the cable or raceway is not less than 32 mm (1¼ in.) from the nearest edge of the framing member or furring strips where nails or screws are likely to penetrate. Where this distance cannot be maintained, the cable or raceway shall be protected from penetration by nails or screws by a steel plate, sleeve, or equivalent at least 1.6 mm (1/16 in.) thick.

Exception No. 1: Steel plates, sleeves, or the equivalent shall not be required to protect rigid metal conduit, intermediate metal conduit, rigid nonmetallic conduit, or electrical metallic tubing.

Exception No. 2: For concealed work in finished buildings, or finished panels for prefabricated buildings where such supporting is impracticable, it shall be permissible to fish the cables between access points.

Exception No. 3: A listed and marked steel plate less than 1.6 mm (1/16 in.) thick that provides equal or better protection against nail or screw penetration shall be permitted.

(E) Cables, Raceways, or Boxes Installed in or Under Roof Decking. A cable, raceway, or box, installed in exposed or concealed locations under metal-corrugated sheet roof decking, shall be installed and supported so there is not less than 38 mm (1½ in.) measured from the lowest surface of the roof decking to the top of the cable, raceway, or box. A cable, raceway, or box shall not be installed in concealed locations in metal-corrugated, sheet decking-type roof.

Informational Note: Roof decking material is often repaired or replaced after the initial raceway or cabling and roofing installation and may be penetrated by the screws or other mechanical devices designed to provide “hold down” strength of the waterproof membrane or roof insulating material.

Exception: Rigid meted conduit and intermediate metal conduit shall not be required to comply with 300.4(E).

(F) Cables and Raceways Installed in Shallow Grooves. Cable- or raceway-type wiring methods installed in a groove, to be covered by wallboard, siding, paneling, carpeting, or similar finish, shall be protected by 1.6 mm (1/16 in.) thick steel plate, sleeve, or equivalent or by not less than 32-mm (1¼-in.) free space for the full length of the groove in which the cable or raceway is installed.

Exception No. 1: Steel plates, sleeves, or the equivalent shall not be required to protect rigid metal conduit, intermediate metal conduit, rigid nonmetallic conduit, or electrical metallic tubing.

Exception No. 2: A listed and marked steel plate less than 1.6 mm (1/16 in.) thick that provides equal or better protection against nail or screw penetration shall be permitted.

(G) Insulated Fittings. Where raceways contain 4 AWG or larger insulated circuit conductors, and these conductors enter a cabinet, a box, an enclosure, or a raceway, the conductors shall be protected by an identified fitting providing a smoothly rounded insulating surface, unless the conductors are separated from the fitting or raceway by identified insulating material that is securely fastened in place.

Exception: Where threaded hubs or bosses that are an integral part of a cabinet, box, enclosure, or raceway provide a smoothly rounded or flared entry for conductors.

Conduit bushings constructed wholly of insulating material shall not be used to secure a fitting or raceway. The insulating fitting or insulating material shall have a temperature rating not less than the insulation temperature rating of the installed conductors.

(H) Structural Joints. A listed expansion/deflection fitting or other approved means shall be used where a raceway crosses a structural joint intended for expansion, contraction or deflection, used in buildings, bridges, parking garages, or other structures.

300.5 Underground Installations.

(A) Minimum Cover Requirements. Direct-buried cable or conduit or other raceways shall be installed to meet the minimum cover requirements of Table 300.5.

(B) Wet Locations. The interior of enclosures or raceways installed underground shall be considered to be a wet location. Insulated conductors and cables installed in these enclosures or raceways in underground installations shall be listed for use in wet locations and shall comply with 310.10(C). Any connections or splices in an underground installation shall be approved for wet locations.

(C) Underground Cables Under Buildings. Underground cable installed under a building shall be in a raceway.

Exception No. 1: Type MI Cable shall be permitted under a building without installation in a raceway where embedded in concrete, fill, or other masonry in accordance with 332.10(6) or in underground runs where suitably protected against physical damage and corrosive conditions in accordance with 332.10(10).

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Table 300.5 Minimum Cover Requirements, 0 to 600 Volts, Nominal, Burial in Millimeters (Inches)
Type of Wiring Method or Circuit
Location of Wiring Method or Circuit Column 1 Direct Burial Cables or Conductors Column 2 Rigid Metal Conduit or Intermediate Metal Conduit Column 3 Nonmetallic Raceways Listed for Direct Burial Without Concrete Encasement or Other Approved Raceways Column 4 Residential Branch Circuits Rated 120 Volts or Less with GFCI Protection and Maximum Overcurrent Protection of 20 Amperes Column 5 Circuits for Control of Irrigation and Landscape Lighting Limited to Not More Than 30 Volts and Installed with Type UF or in Other Identified Cable or Raceway
mm in. mm in. mm in. mm in. mm in.
All locations not specified below 600 24 150 6 450 18 300 12 150 6
In trench below 50-mm (2-in.) thick concrete or equivalent 450 18 150 6 300 12 150 6 150 6
Under a building 0 0 0 0 0 0 0 0 0 0
(in raceway or Type MC or Type MI cable identified for direct burial) (in raceway or Type MC or Type MI cable identified for direct burial) (in raceway or Type MC or Type MI cable identified for direct burial)
Under minimum of 102-mm (4-in.) thick concrete exterior slab with no vehicular traffic and the slab extending not less than 152 mm (6 in.) beyond the underground installation 450 18 100 4 100 4 150 6 150 6
(direct burial) (direct burial)
100 4 100 4
(in raceway) (in raceway)
Under streets, highways, roads, alleys, driveways, and parking lots 600 24 600 24 600 24 600 24 600 24
One- and two-family dwelling driveways and outdoor parking areas, and used only for dwelling-related purposes 450 18 450 18 450 18 300 12 450 18
In or under airport runways, including adjacent areas where trespassing prohibited 450 18 450 18 450 18 450 18 450 18
Notes:
1. Cover is defined as the shortest distance in millimeters (inches) measured between a point on the top surface of any direct-buried conductor, cable, conduit, or other raceway and the top surface of finished grade, concrete, or similar cover.
2. Raceways approved for burial only where concrete encased shall require concrete envelope not less than 50 mm (2 in.) thick.
3. Lesser depths shall be permitted where cables and conductors rise for terminations or splices or where access is otherwise required.
4. Where one of the wiring method types listed in Columns 1-3 is used for one of the circuit types in Columns 4 and 5, the shallowest depth of burial shall be permitted.
5. Where solid rock prevents compliance with the cover depths specified in this table, the wiring shall be installed in metal or nonmetallic raceway permitted for direct burial. The raceways shall be covered by a minimum of 50 mm (2 in.) of concrete extending down to rock.
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Exception No. 2: Type MC Cable listed for direct burial or concrete encasement shall be permitted under a building without installation in a raceway in accordance with 330.10(A)(5) and in wet locations in accordance with 330.10(11).

(D) Protection from Damage. Direct-buried conductors and cables shall be protected from damage in accordance with 300.5(D)(1) through (D)(4).

(1) Emerging from Grade. Direct-buried conductors and cables emerging from grade and specified in columns 1 and 4 of Table 300.5 shall be protected by enclosures or raceways extending from the minimum cover distance below grade required by 300.5(A) to a point at least 2.5 m (8 ft) above finished grade. In no case shall the protection be required to exceed 450 mm (18 in.) below finished grade.

(2) Conductors Entering Buildings. Conductors entering a building shall be protected to the point of entrance.

(3) Service Conductors. Underground service conductors that are not encased in concrete and that are buried 450 mm (18 in.) or more below grade shall have their location identified by a warning ribbon that is placed in the trench at least 300 mm (12 in.) above the underground installation.

(4) Enclosure or Raceway Damage. Where the enclosure or raceway is subject to physical damage, the conductors shall be installed in rigid metal conduit, intermediate metal conduit, Schedule 80 PVC conduit, or equivalent.

(E) Splices and Taps. Direct-buried conductors or cables shall be permitted to be spliced or tapped without the use of splice boxes. The splices or taps shall be made in accordance with 110.14(B).

(F) Backfill. Backfill that contains large rocks, paving materials, cinders, large or sharply angular substances, or corrosive material shall not be placed in an excavation where materials may damage raceways, cables, or other substructures or prevent adequate compaction of fill or contribute to corrosion of raceways, cables, or other substructures.

Where necessary to prevent physical damage to the raceway or cable, protection shall be provided in the form of granular or selected material, suitable running boards, suitable sleeves, or other approved means.

(G) Raceway Seals. Conduits or raceways through which moisture may contact live parts shall be sealed or plugged at either or both ends.

Informational Note: Presence of hazardous gases or vapors may also necessitate sealing of underground conduits or raceways entering buildings.

(H) Bushing. A bushing, or terminal fitting, with an integral bushed opening shall be used at the end of a conduit or other raceway that terminates underground where the conductors or cables emerge as a direct burial wiring method. A seal incorporating the physical protection characteristics of a bushing shall be permitted to be used in lieu of a bushing.

(I) Conductors of the Same Circuit. All conductors of the same circuit and, where used, the grounded conductor and all equipment grounding conductors shall be installed in the same raceway or cable or shall be installed in close proximity in the same trench.

Exception No. 1: Conductors shall be permitted to be installed in parallel in raceways, multiconductor cables, or direct-buried single conductor cables. Each raceway or multiconductor cable shall contain all conductors of the same circuit, including equipment grounding conductors. Each direct-buried single conductor cable shall be located in close proximity in the trench to the other single conductor cables in the same parallel set of conductors in the circuit, including equipment grounding conductors.

Exception No. 2: Isolated phase, polarity, grounded conductor, and equipment grounding and bonding conductor installations shall be permitted in nonmetallic raceways or cables with a nonmetallic covering or nonmagnetic sheath in close proximity where conductors are paralleled as permitted in 310.10(H), and where the conditions of 300.20(B) are met.

(J) Earth Movement. Where direct-buried conductors, raceways, or cables are subject to movement by settlement or frost, direct-buried conductors, raceways, or cables shall be arranged so as to prevent damage to the enclosed conductors or to equipment connected to the raceways.

Informational Note: This section recognizes “S” loops in underground direct burial to raceway transitions, expansion fittings in raceway risers to fixed equipment, and, generally, the provision of flexible connections to equipment subject to settlement or frost heaves.

(K) Directional Boring. Cables or raceways installed using directional boring equipment shall be approved for the purpose.

300.6 Protection Against Corrosion and Deterioration.

Raceways, cable trays, cablebus, auxiliary gutters, cable armor, boxes, cable sheathing, cabinets, elbows, couplings, fittings, supports, and support hardware shall be of materials suitable for the environment in which they are to be installed.

(A) Ferrous Metal Equipment. Ferrous metal raceways, cable trays, cablebus, auxiliary gutters, cable armor, boxes, cable sheathing, cabinets, metal elbows, couplings, nipples, fittings, supports, and support hardware shall be suitably protected against corrosion inside and outside (except threads at joints) by a coating of approved corrosion-resistant material. Where corrosion protection is necessary and the conduit is threaded in the field, the threads shall be

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coated with an approved electrically conductive, corrosion-resistant compound.

Exception: Stainless steel shall not be required to have protective coatings.

(1) Protected from Corrosion Solely by Enamel. Where protected from corrosion solely by enamel, ferrous metal raceways, cable trays, cablebus, auxiliary gutters, cable armor, boxes, cable sheathing, cabinets, metal elbows, couplings, nipples, fittings, supports, and support hardware shall not be used outdoors or in wet locations as described in 300.6(D).

(2) Organic Coatings on Boxes or Cabinets. Where boxes or cabinets have an approved system of organic coatings and are marked “Raintight,” “Rainproof,” or “Outdoor Type,” they shall be permitted outdoors.

(3) In Concrete or in Direct Contact with the Earth. Ferrous metal raceways, cable armor, boxes, cable sheathing, cabinets, elbows, couplings, nipples, fittings, supports, and support hardware shall be permitted to be installed in concrete or in direct contact with the earth, or in areas subject to severe corrosive influences where made of material approved for the condition, or where provided with corrosion protection approved for the condition.

(B) Aluminum Metal Equipment. Aluminum raceways, cable trays, cablebus, auxiliary gutters, cable armor, boxes, cable sheathing, cabinets, elbows, couplings, nipples, fittings, supports, and support hardware embedded or encased in concrete or in direct contact with the earth shall be provided with supplementary corrosion protection.

(C) Nonmetallic Equipment. Nonmetallic raceways, cable trays, cablebus, auxiliary gutters, boxes, cables with a non-metallic outer jacket and internal metal armor or jacket, cable sheathing, cabinets, elbows, couplings, nipples, fittings, supports, and support hardware shall be made of material approved for the condition and shall comply with (C) (1) and (C)(2) as applicable to the specific installation.

(1) Exposed to Sunlight. Where exposed to sunlight, the materials shall be listed as sunlight resistant or shall be identified as sunlight resistant.

(2) Chemical Exposure. Where subject to exposure to chemical solvents, vapors, splashing, or immersion, materials or coatings shall either be inherently resistant to chemicals based on their listing or be identified for the specific chemical reagent.

(D) Indoor Wet Locations. In portions of dairy processing facilities, laundries, canneries, and other indoor wet locations, and in locations where walls are frequently washed or where there are surfaces of absorbent materials, such as damp paper or wood, the entire wiring system, where installed exposed, including all boxes, fittings, raceways, and cable used therewith, shall be mounted so that there is at least a 6-mm (¼-in.) airspace between it and the wall or supporting surface.

Exception: Nonmetallic raceways, boxes, and fittings shall be permitted to be installed without the airspace on a concrete, masonry, tile, or similar surface.

Informational Note: In general, areas where acids and alkali chemicals are handled and stored may present such corrosive conditions, particularly when wet or damp. Severe corrosive conditions may also be present in portions of meatpacking plants, tanneries, glue houses, and some stables; in installations immediately adjacent to a seashore and swimming pool areas; in areas where chemical deicers are used; and in storage cellars or rooms for hides, casings, fertilizer, salt, and bulk chemicals.

300.7 Raceways Exposed to Different Temperatures.

(A) Sealing. Where portions of a raceway or sleeve are known to be subjected to different temperatures, and where condensation is known to be a problem, as in cold storage areas of buildings or where passing from the interior to the exterior of a building, the raceway or sleeve shall be filled with an approved material to prevent the circulation of warm air to a colder section of the raceway or sleeve. An explosionproof seal shall not be required for this purpose.

(B) Expansion Fittings. Raceways shall be provided with expansion fittings where necessary to compensate for thermal expansion and contraction.

Informational Note: Table 352.44 and Table 355.44 provide the expansion information for polyvinyl chloride (PVC) and for reinforced thermosetting resin conduit (RTRC), respectively. A nominal number for steel conduit can be determined by multiplying the expansion length in Table 352.44 by 0.20. The coefficient of expansion for steel electrical metallic tubing, intermediate metal conduit, and rigid conduit is 1.170× 10–5 (0.0000117 mm per mm of conduit for each °C in temperature change) [0.650 × 10–5(0.0000065 in. per inch of conduit for each °F in temperature change)].

A nominal number for aluminum conduit and aluminum electrical metallic tubing can be determined by multiplying the expansion length in Table 352.44 by 0.40. The coefficient of expansion for aluminum electrical metallic tubing and aluminum rigid metal conduit is 2.34 × 10–5(0.0000234 mm per mm of conduit for each °C in temperature change) [1.30 × 10–5 (0.000013) in. per inch of conduit for each °F in temperature change].

300.8 Installation of Conductors with Other Systems. Raceways or cable trays containing electrical conductors shall not contain any pipe, tube, or equal for steam, water, air, gas, drainage, or any service other than electrical.

300.9 Raceways in Wet Locations Abovegrade. Where raceways are installed in wet locations abovegrade, the interior

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of these raceways shall be considered to be a wet location. Insulated conductors and cables installed in raceways in wet locations abovegrade shall comply with 310.10(C).

300.10 Electrical Continuity of Metal Raceways and Enclosures. Metal raceways, cable armor, and other metal enclosures for conductors shall be metallically joined together into a continuous electrical conductor and shall be connected to all boxes, fittings, and cabinets so as to provide effective electrical continuity. Unless specifically permitted elsewhere in this Code, raceways and cable assemblies shall be mechanically secured to boxes, fittings, cabinets, and other enclosures.

Exception No. 1: Short sections of raceways used to provide support or protection of cable assemblies from physical damage shall not be required to be made electrically continuous.

Exception No. 2: Equipment enclosures to be isolated, as permitted by 250.96(B), shall not be required to be metallically joined to the metal raceway.

300.11 Securing and Supporting.

(A) Secured in Place. Raceways, cable assemblies, boxes, cabinets, and fittings shall be securely fastened in place. Support wires that do not provide secure support shall not be permitted as the sole support. Support wires and associated fittings that provide secure support and that are installed in addition to the ceiling grid support wires shall be permitted as the sole support. Where independent support wires are used, they shall be secured at both ends. Cables and raceways shall not be supported by ceiling grids.

(1) Fire-Rated Assemblies. Wiring located within the cavity of a fire-rated floor-ceiling or roof-ceiling assembly shall not be secured to, or supported by, the ceiling assembly, including the ceiling support wires. An independent means of secure support shall be provided and shall be permitted to be attached to the assembly. Where independent support wires are used, they shall be distinguishable by color, tagging, or other effective means from those that are part of the fire-rated design.

Exception: The ceiling support system shall be permitted to support wiring and equipment that have been tested as part of the fire-rated assembly.

Informational Note: One method of determining fire rating is testing in accordance with NFPA 251-2006, Standard Methods of Tests of Fire Resistance of Building Construction and Materials.

(2) Non-Fire-Rated Assemblies. Wiring located within the cavity of a non-fire-rated floor-ceiling or roof-ceiling assembly shall not be secured to, or supported by, the ceiling assembly, including the ceiling support wires. An independent means of secure support shall be provided and shall be permitted to be attached to the assembly. Where independent support wires are used, they shall be distinguishable by color, tagging, or other effective means.

Exception: The ceiling support system shall be permitted to support branch-circuit wiring and associated equipment where installed in accordance with the ceiling system manufacturer’s instructions.

(B) Raceways Used as Means of Support. Raceways shall be used only as a means of support for other raceways, cables, or nonelectrical equipment under any of the following conditions:

  1. Where the raceway or means of support is identified for the purpose
  2. Where the raceway contains power supply conductors for electrically controlled equipment and is used to support Class 2 circuit conductors or cables that are solely for the purpose of connection to the equipment control circuits
  3. Where the raceway is used to support boxes or conduit bodies in accordance with 314.23 or to support luminaires in accordance with 410.36(E)

(C) Cables Not Used as Means of Support. Cable wiring methods shall not be used as a means of support for other cables, raceways, or nonelectrical equipment.

300.12 Mechanical Continuity — Raceways and Cables. Metal or nonmetallic raceways, cable armors, and cable sheaths shall be continuous between cabinets, boxes, fittings, or other enclosures or outlets.

Exception No. 1: Short sections of raceways used to provide support or protection of cable assemblies from physical damage shall not be required to be mechanically continuous.

Exception No. 2: Raceways and cables installed into the bottom of open bottom equipment, such as switchboards, motor control centers, and floor or pad-mounted transformers, shall not be required to be mechanically secured to the equipment.

300.13 Mechanical and Electrical Continuity — Conductors.

(A) General. Conductors in raceways shall be continuous between outlets, boxes, devices, and so forth. There shall be no splice or tap within a raceway unless permitted by 300.15: 368.56(A); 376.56; 378.56; 384.56; 386.56; 388.56; or 390.7.

(B) Device Removal. In multiwire branch circuits, the continuity of a grounded conductor shall not depend on device connections such as lampholders, receptacles, and so forth, where the removal of such devices would interrupt the continuity.

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300.14 Length of Free Conductors at Outlets, Junctions, and Switch Points. At least 150 mm (6 in.) of free conductor, measured from the point in the box where it emerges from its raceway or cable sheath, shall be left at each outlet, junction, and switch point for splices or the connection of luminaires or devices. Where the opening to an outlet, junction, or switch point is less than 200 mm (8 in.) in any dimension, each conductor shall be long enough to extend at least 75 mm (3 in.) outside the opening.

Exception: Conductors that are not spliced or terminated at the outlet, junction, or switch point shall not be required to comply with 300.14.

300.15 Boxes, Conduit Bodies, or Fittings — Where Required. A box shall be installed at each outlet and switch point for concealed knob-and-tube wiring.

Fittings and connectors shall be used only with the specific wiring methods for which they are designed and listed.

Where the wiring method is conduit, tubing, Type AC cable. Type MC cable, Type MI cable, nonmetallic-sheathed cable, or other cables, a box or conduit body shall be installed at each conductor splice point, outlet point, switch point, junction point, termination point, or pull point, unless otherwise permitted in 300.15(A) through (L).

(A) Wiring Methods with Interior Access. A box or conduit body shall not be required for each splice, junction, switch, pull, termination, or outlet points in wiring methods with removable covers, such as wireways, multioutlet assemblies, auxiliary gutters, and surface raceways. The covers shall be accessible after installation.

(B) Equipment. An integral junction box or wiring compartment as part of approved equipment shall be permitted in lieu of a box.

(C) Protection. A box or conduit body shall not be required where cables enter or exit from conduit or tubing that is used to provide cable support or protection against physical damage. A fitting shall be provided on the end(s) of the conduit or tubing to protect the cable from abrasion.

(D) Type MI Cable. A box or conduit body shall not be required where accessible fittings are used for straight-through splices in mineral-insulated metal-sheathed cable.

(E) Integral Enclosure. A wiring device with integral enclosure identified for the use, having brackets that securely fasten the device to walls or ceilings of conventional on-site frame construction, for use with nonmetallic-sheathed cable, shall be permitted in lieu of a box or conduit body.

Informational Note: See 334.30(C); 545.10; 550.15(1); 551.47(E), Exception No. 1; and 552.48(E), Exception No. 1.

(F) Fitting. A fitting identified for the use shall be permitted in lieu of a box or conduit body where conductors are not spliced or terminated within the fitting. The fitting shall be accessible after installation.

(G) Direct-Buried Conductors. As permitted in 300.5(E), a box or conduit body shall not be required for splices and taps in direct-buried conductors and cables.

(H) Insulated Devices. As permitted in 334.40(B), a box or conduit body shall not be required for insulated devices supplied by nonmetallic-sheathed cable.

(I) Enclosures. A box or conduit body shall not be required where a splice, switch, terminal, or pull point is in a cabinet or cutout box, in an enclosure for a switch or overcurrent device as permitted in 312.8, in a motor controller as permitted in 430.10(A), or in a motor control center.

(J) Luminaires. A box or conduit body shall not be required where a luminaire is used as a raceway as permitted in 410.64.

(K) Embedded. A box or conduit body shall not be required for splices where conductors are embedded as permitted in 424.40, 424.41(D), 426.22(B), 426.24(A), and 427.19(A).

(L) Manholes and Handhole Enclosures. A box or conduit body shall not be required for conductors in manholes or handhole enclosures, except where connecting to electrical equipment. The installation shall comply with the provisions of Part V of Article 110 for manholes, and 314.30 for handhole enclosures.

300.16 Raceway or Cable to Open or Concealed Wiring.

(A) Box, Conduit Body, or Fitting. A box, conduit body, or terminal fitting having a separately bushed hole for each conductor shall be used wherever a change is made from conduit, electrical metallic tubing, electrical nonmetallic tubing, nonmetallic-sheathed cable, Type AC cable, Type MC cable, or mineral-insulated, metal-sheathed cable and surface raceway wiring to open wiring or to concealed knob-and-tube wiring. A fitting used for this purpose shall contain no taps or splices and shall not be used at luminaire outlets. A conduit body used for this purpose shall contain no taps or splices, unless it complies with 314.16(C)(2).

(B) Bushing. A bushing shall be permitted in lieu of a box or terminal where the conductors emerge from a raceway and enter or terminate at equipment, such as open switchboards, unenclosed control equipment, or similar equipment. The bushing shall be of the insulating type for other than lead-sheathed conductors.

300.17 Number and Size of Conductors in Raceway. The number and size of conductors in any raceway shall not be more than will permit dissipation of the heat and ready installation or withdrawal of the conductors without damage to the conductors or to their insulation.

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Informational Note: See the following sections of this Code: intermediate metal conduit, 342.22; rigid metal conduit, 344.22; flexible metal conduit, 348.22; liquidtight flexible metal conduit, 350.22; PVC conduit, 352.22; HDPE conduit, 353.22; RTRC, 355.22; liquidtight nonmetallic flexible conduit, 356.22; electrical metallic tubing, 358.22; flexible metallic tubing, 360.22; electrical nonmetallic tubing, 362.22; cellular concrete floor raceways, 372.11; cellular metal floor raceways, 374.5; metal wire-ways, 376.22; nonmetallic wireways, 378.22; surface metal raceways, 386.22; surface nonmetallic raceways, 388.22; underfloor raceways, 390.6; fixture wire, 402.7; theaters, 520.6; signs, 600.31(C); elevators, 620.33; audio signal processing, amplification, and reproduction equipment, 640.23(A) and 640.24; Class 1, Class 2, and Class 3 circuits, Article 725; fire alarm circuits, Article 760; and optical fiber cables and raceways. Article 770.

300.18 Raceway Installations.

(A) Complete Runs. Raceways, other than busways or exposed raceways having hinged or removable covers, shall be installed complete between outlet, junction, or splicing points prior to the installation of conductors. Where required to facilitate the installation of utilization equipment, the raceway shall be permitted to be initially installed without a terminating connection at the equipment. Prewired raceway assemblies shall be permitted only where specifically permitted in this Code for the applicable wiring method.

Exception: Short sections of raceways used to contain conductors or cable assemblies for protection from physical damage shall not be required to be installed complete between outlet, junction, or splicing points.

(B) Welding. Metal raceways shall not be supported, terminated, or connected by welding to the raceway unless specifically designed to be or otherwise specifically permitted to be in this Code.

300.19 Supporting Conductors in Vertical Raceways.

(A) Spacing Intervals — Maximum. Conductors in vertical raceways shall be supported if the vertical rise exceeds the values in Table 300.19(A). One cable support shall be provided at the top of the vertical raceway or as close to the top as practical. Intermediate supports shall be provided as necessary to limit supported conductor lengths to not greater than those values specified in Table 300.19(A).

Exception: Steel wire armor cable shall be supported at the top of the riser with a cable support that clamps the steel wire armor. A safety device shall be permitted at the lower end of the riser to hold the cable in the event there is slippage of the cable in the wire-armored cable support. Additional wedge-type supports shall be permitted to relieve the strain on the equipment terminals caused by expansion of the cable under load.

(B) Fire-Rated Cables and Conductors. Support methods and spacing intervals for fire-rated cables and conductors shall comply with any restrictions provided in the listing of the electrical circuit protective system used and in no case shall exceed the values in Table 300.19(A).

(C) Support Methods. One of the following methods of support shall be used:

  1. By clamping devices constructed of or employing insulating wedges inserted in the ends of the raceways. Where clamping of insulation does not adequately support the cable, the conductor also shall be clamped.
  2. By inserting boxes at the required intervals in which insulating supports are installed and secured in a satisfactory manner to withstand the weight of the conductors attached thereto, the boxes being provided with covers.
    Table 300.19(A) Spacings for Conductor Supports
        Conductors
    Conductor Size Support of
    Conductors in
    Vertical Raceways
    Aluminum or
    Copper-Clad
    Aluminum
    Copper
    m ft m ft
    18 AWG through 8 AWG Not greater than 30 100 30 100
    6 AWG through 1/0 AWG Not greater than 60 200 30 100
    2/0 AWG through 4/0 AWG Not greater than 55 180 25   80
    Over 4/0 AWG through 350 kcmil Not greater than 41 135 18   60
    Over 350 kcmil through 500 kcmil Not greater than 36 120 15   50
    Over 500 kcmil through 750 kcmil Not greater than 28   95 12   40
    Over 750 kcmil Not greater than 26   85 11   35
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  3. In junction boxes, by deflecting the cables not less than 90 degrees and carrying them horizontally to a distance not less than twice the diameter of the cable, the cables being carried on two or more insulating supports and additionally secured thereto by tie wires if desired. Where this method is used, cables shall be supported at intervals not greater than 20 percent of those mentioned in the preceding tabulation.
  4. By a method of equal effectiveness.

300.20 Induced Currents in Ferrous Metal Enclosures or Ferrous Metal Raceways.

(A) Conductors Grouped Together. Where conductors carrying alternating current are installed in ferrous metal enclosures or ferrous metal raceways, they shall be arranged so as to avoid heating the surrounding ferrous metal by induction. To accomplish this, all phase conductors and, where used, the grounded conductor and all equipment grounding conductors shall be grouped together.

Exception No. 1: Equipment grounding conductors for certain existing installations shall be permitted to be installed separate from their associated circuit conductors where run in accordance with the provisions of 250.130(C).

Exception No. 2: A single conductor shall be permitted to be installed in a ferromagnetic enclosure and used for skin-effect heating in accordance with the provisions of 426.42 and 427.47.

(B) Individual Conductors. Where a single conductor carrying alternating current passes through metal with magnetic properties, the inductive effect shall be minimized by (1) cutting slots in the metal between the individual holes through which the individual conductors pass or (2) passing all the conductors in the circuit through an insulating wall sufficiently large for all of the conductors of the circuit.

Exception: In the case of circuits supplying vacuum or electric-discharge lighting systems or signs or X-ray apparatus, the currents carried by the conductors are so small that the inductive heating effect can be ignored where these conductors are placed, in metal enclosures or pass through metal.

Informational Note: Because aluminum is not a magnetic metal, there will be no heating due to hysteresis; however, induced currents will be present. They will not be of sufficient magnitude to require grouping of conductors or special treatment in passing conductors through aluminum wall sections.

300.21 Spread of Fire or Products of Combustion. Electrical installations in hollow spaces, vertical shafts, and ventilation or air-handling ducts shall be made so that the possible spread of fire or products of combustion will not be substantially increased. Openings around electrical penetrations into or through fire-resistant-rated walls, partitions, floors, or ceilings shall be firestopped using approved methods to maintain the fire resistance rating.

Informational Note: Directories of electrical construction materials published by qualified testing laboratories contain many listing installation restrictions necessary to maintain the fire-resistive rating of assemblies where penetrations or openings are made. Building codes also contain restrictions on membrane penetrations on opposite sides of a fire-resistance-rated wall assembly. An example is the 600-mm (24-in.) minimum horizontal separation that usually applies between boxes installed on opposite sides of the wall. Assistance in complying with 300.21 can be found in building codes, fire resistance directories, and product listings.

300.22 Wiring in Ducts Not Used for Air Handling, Fabricated Ducts for Environmental Air, and Other Spaces for Environmental Air (Plenums). The provisions of this section shall apply to the installation and uses of electrical wiring and equipment in ducts used for dust, loose stock, or vapor removal: ducts specifically fabricated for environmental air; and other spaces used for environmental air (plenums).

Informational Note: See Article 424, Part VI, for duct heaters.

(A) Ducts for Dust, Loose Stock, or Vapor Removal. No wiring systems of any type shall be installed in ducts used to transport dust, loose stock, or flammable vapors. No wiring system of any type shall be installed in any duct, or shaft containing only such ducts, used for vapor removal or for ventilation of commercial-type cooking equipment.

(B) Ducts Specifically Fabricated for Environmental Air. Only wiring methods consisting of Type MI cable, Type MC cable employing a smooth or corrugated impervious metal sheath without an overall nonmetallic covering, electrical metallic tubing, flexible metallic tubing, intermediate metal conduit, or rigid metal conduit without an overall nonmetallic covering shall be installed in ducts specifically fabricated to transport environmental air. Flexible metal conduit shall be permitted, in lengths not to exceed 1.2 m (4 ft), to connect physically adjustable equipment and devices permitted to be in these fabricated ducts. The connectors used with flexible metal conduit shall effectively close any openings in the connection. Equipment and devices shall be permitted within such ducts only if necessary for the direct action upon, or sensing of, the contained air. Where equipment or devices are installed and illumination is necessary to facilitate maintenance and repair, enclosed gasketed-type luminaires shall be permitted.

(C) Other Spaces Used for Environmental Air (Plenums). This section shall apply to spaces not specifically fabricated for environmental air-handling purposes but used for air-handling purposes as a plenum. This section shall

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not apply to habitable rooms or areas of buildings, the prime purpose of which is not air handling.

Informational Note No. 1: The space over a hung ceiling used for environmental air-handling purposes is an example of the type of other space to which this section applies.

Informational Note No. 2: The phrase “Other Spaces Used for Environmental Air (Plenum)” as used in this section correlates with the use of the term “plenum” in NFPA 90A-2009, Standard for the Installation of Air-Conditioning and Ventilating Systems, and other mechanical codes where the plenum is used for return air purposes, as well as some other air-handling spaces.

Exception: This section shall not apply to the joist or stud spaces of dwelling units where the wiring passes through such spaces perpendicular to the long dimension of such spaces.

(1) Wiring Methods. The wiring methods for such other space shall be limited to totally enclosed, nonventilated, insulated busway having no provisions for plug-in connections, Type MI cable, Type MC cable without an overall nonmetallic covering, Type AC cable, or other factory-assembled multiconductor control or power cable that is specifically listed for use within an air-handling space, or listed prefabricated cable assemblies of metallic manufactured wiring systems without nonmetallic sheath. Other types of cables, conductors, and raceways shall be permitted to be installed in electrical metallic tubing, flexible metallic tubing, intermediate metal conduit, rigid metal conduit without an overall nonmetallic covering, flexible metal conduit, or, where accessible, surface metal raceway or metal wireway with metal covers.

(2) Cable Tray Systems. The provisions in (a) or (b) shall apply to the use of metallic cable tray systems in other spaces used for environmental air (plenums), where accessible, as follows:

(a) Metal Cable Tray Systems. Metal cable tray systems shall be permitted to support the wiring methods in 300.22(C)(1).

(b) Solid Side and Bottom Metal Cable Tray Systems, Solid side and bottom metal cable tray systems with solid metal covers shall be permitted to enclose wiring methods and cables, not already covered in 300.22(C)(1), in accordance with 392.10(A) and (B).

(3) Equipment. Electrical equipment with a metal enclosure, or electrical equipment with a nonmetallic enclosure listed for use within an air-handling space and having adequate fire-resistant and low-smoke-producing characteristics, and associated wiring material suitable for the ambient temperature shall be permitted to be installed in such other space unless prohibited elsewhere in this Code.

Informational Note: One method of defining adequate fire-resistant and low-smoke producing characteristics for electrical equipment with a nonmetallic enclosure is in ANS1/UL 2043-2008, Fire Test for Heat and Visible Smoke Release for Discrete Products and Their Accessories Installed in Air-Handling Spaces.

Exception: Integral fan systems shall be permitted where specifically identified for use within an air-handling space.

(D) Information Technology Equipment. Electrical wiring in air-handling areas beneath raised floors for information technology equipment shall be permitted in accordance with Article 645.

300.23 Panels Designed to Allow Access. Cables, raceways, and equipment installed behind panels designed to allow access, including suspended ceiling panels, shall be arranged and secured so as to allow the removal of panels and access to the equipment.

II. Requirements for over 600 Volts, Nominal

300.31 Covers Required. Suitable covers shall be installed on all boxes, fittings, and similar enclosures to prevent accidental contact with energized parts or physical damage to parts or insulation.

300.32 Conductors of Different Systems. See 300.3(C)(2).

300.34 Conductor Bending Radius. The conductor shall not be bent to a radius less than 8 times the overall diameter for nonshielded conductors or 12 times the overall diameter for shielded or lead-covered conductors during or after installation. For multiconductor or multiplexed single-conductor cables having individually shielded conductors, the minimum bending radius is 12 times the diameter of the individually shielded conductors or 7 times the overall diameter, whichever is greater.

300.35 Protection Against Induction Heating. Metallic raceways and associated conductors shall be arranged so as to avoid heating of the raceway in accordance with the applicable provisions of 300.20.

300.37 Aboveground Wiring Methods. Aboveground conductors shall be installed in rigid metal conduit, in intermediate metal conduit, in electrical metallic tubing, in RTRC and PVC conduit, in cable trays, in auxiliary gutters, as busways, as cablebus, in other identified raceways, or as exposed runs of metal-clad cable suitable for the use and purpose. In locations accessible to qualified persons only, exposed runs of Type MV cables, bare conductors, and bare busbars shall also be permitted. Busbars shall be permitted to be either copper or aluminum.

300.39 Braid-Covered Insulated Conductors — Exposed Installation. Exposed runs of braid-covered insulated conductors shall have a flame-retardant braid. If the

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conductors used do not have this protection, a flame-retardant saturant shall be applied to the braid covering after installation. This treated braid covering shall be stripped back a safe distance at conductor terminals, according to the operating voltage. Where practicable, this distance shall not be less than 25 mm (1 in.) for each kilovolt of the conductor-to-ground voltage of the circuit.

300.40 Insulation Shielding. Metallic and semiconducting insulation shielding components of shielded cables shall be removed for a distance dependent on the circuit voltage and insulation. Stress reduction means shall be provided at all terminations of factory-applied shielding.

Metallic shielding components such as tapes, wires, or braids, or combinations thereof, shall be connected to a grounding conductor, grounding busbar, or a grounding electrode.

300.42 Moisture or Mechanical Protection for Metal-Sheathed Cables. Where cable conductors emerge from a metal sheath and where protection against moisture or physical damage is necessary, the insulation of the conductors shall be protected by a cable sheath terminating device.

300.50 Underground Installations.

(A) General. Underground conductors shall be identified for the voltage and conditions under which they are installed. Direct-burial cables shall comply with the provisions of 310.10(F). Underground cables shall be installed in accordance with 300.50(A)(1) or (A)(2), and the installation shall meet the depth requirements of Table 300.50.

(1) Shielded Cables and Nonshielded Cables in Metal-Sheathed Cable Assemblies. Underground cables, including

Table 300.50 Minimum Covera Requirements
Circuit Voltage General Conditions (not otherwise specified) Special Conditions (use if applicable)
Column 1 Column 2 Column 3 Column 4 Column 5 Column 6
Direct-Buried Cablesd RTRC, PVC, and HOPE Conduitb Rigid Metal Conduit and Intermediate Metal Conduit Raceways Under Buildings or Exterior Concrete Slabs, 100 mm (4 in.) Minimum Thicknessc Cables in Airport Runways or Adjacent Areas Where Trespass Is Prohibited Areas Subject to Vehicular Traffic, Such as Thoroughfares and Commercial Parking Areas
mm in. mm in. mm in. mm in. mm in. mm in.
Over 600 V through 22 kV 750 30 450 18 150 6 100 4 450 18 600 24
Over 22 kV through 40 kV 900 36 600 24 150 6 100 4 450 18 600 24
Over 40 kV 1000 42 750 30 150 6 100 4 450 18 600 24
General Notes:
1. Lesser depths shall be permitted where cables and conductors rise for terminations or splices or where access is otherwise required.
2. Where solid rock prevents compliance with the cover depths specified in this table, the wiring shall be installed in a metal or nonmetallic raceway permitted for direct burial. The raceways shall be covered by a minimum of 50 mm (2 in.) of concrete extending down to rock.
3. In industrial establishments, where conditions of maintenance and supervision ensure that qualified persons will service the installation, the minimum cover requirements, for other than rigid metal conduit and intermediate metal conduit, shall be permitted to be reduced 150 mm (6 in.) for each 50 mm (2 in.) of concrete or equivalent placed entirely within the trench over the underground installation.
Specific Footnotes:
a Cover is defined as the shortest distance in millimeters (inches) measured between a point on the top surface of any direct-buried conductor, cable, conduit, or other raceway and the top surface of finished grade, concrete, or similar cover.
b Listed by a qualified testing agency as suitable for direct burial without encasement. All other nonmetallic systems shall require 50 mm (2 in.) of concrete or equivalent above conduit in addition to the table depth.
c The slab shall extend a minimum of 150 mm (6 in.) beyond the underground installation, and a warning ribbon or other effective means suitable for the conditions shall be placed above the underground installation.
d Underground direct-buried cables that are not encased or protected by concrete and are buried 750 mm (30 in.) or more below grade shall have their location identified by a warning ribbon that is placed in the trench at least 300 mm (12 in.) above the cables.
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nonshielded. Type MC and moisture-impervious metal sheath cables, shall have those sheaths grounded through an effective grounding path meeting the requirements of 250.4(A)(5) or (B)(4). They shall be direct buried or installed in raceways identified for the use.

(2) Other Nonshielded Cables. Other nonshielded cables not covered in 300.50(A)(1) shall be installed in rigid metal conduit, intermediate metal conduit, or rigid nonmetallic conduit encased in not less than 75 mm (3 in.) of concrete.

(B) Wet Locations. The interior of enclosures or raceways installed underground shall be considered to be a wet location. Insulated conductors and cables installed in these enclosures or raceways in underground installations shall be listed for use in wet locations and shall comply with 310.10(C). Any connections or splices in an underground installation shall be approved for wet locations.

(C) Protection from Damage. Conductors emerging from the ground shall be enclosed in listed raceways. Raceways installed on poles shall be of rigid metal conduit, intermediate metal conduit, RTRC-XW, Schedule 80 PVC conduit, or equivalent, extending from the minimum cover depth specified in Table 300.50 to a point 2.5 m (8 ft) above finished grade. Conductors entering a building shall be protected by an approved enclosure or raceway from the minimum cover depth to the point of entrance. Where direct-buried conductors, raceways, or cables are subject to movement by settlement or frost, they shall be installed to prevent damage to the enclosed conductors or to the equipment connected to the raceways. Metallic enclosures shall be grounded.

(D) Splices. Direct burial cables shall be permitted to be spliced or tapped without the use of splice boxes, provided they are installed using materials suitable for the application. The taps and splices shall be watertight and protected from mechanical damage. Where cables are shielded, the shielding shall be continuous across the splice or tap.

Exception: At splices of an engineered cabling system, metallic shields of direct-buried single-conductor cables with maintained spacing between phases shall be permitted to be interrupted and overlapped. Where shields are interrupted and overlapped, each shield section shall be grounded at one point.

(E) Backfill. Backfill containing large rocks, paving materials, cinders, large or sharply angular substances, or corrosive materials shall not be placed in an excavation where materials can damage or contribute to the corrosion of raceways, cables, or other substructures or where it may prevent adequate compaction of fill.

Protection in the form of granular or selected material or suitable sleeves shall be provided to prevent physical damage to the raceway or cable.

(F) Raceway Seal. Where a raceway enters from an underground system, the end within the building shall be sealed with an identified compound so as to prevent the entrance of moisture or gases, or it shall be so arranged to prevent moisture from contacting live parts.

ARTICLE 310
Conductors for General Wiring

I. General

310.1 Scope. This article covers general requirements for conductors and their type designations, insulations, markings, mechanical strengths, ampacity ratings, and uses. These requirements do not apply to conductors that form an integral part of equipment, such as motors, motor controllers, and similar equipment, or to conductors specifically provided for elsewhere in this Code.

Informational Note: For flexible cords and cables, see Article 400. For fixture wires, see Article 402.

310.2 Definitions.

Electrical Ducts. Electrical conduits, or other raceways round in cross section, that are suitable for use underground or embedded in concrete.

Thermal Resistivity. As used in this Code, the heat transfer capability through a substance by conduction. It is the reciprocal of thermal conductivity and is designated Rho and expressed in the units °C-cm/W.

II. Installation

310.10 Uses Permitted. The conductors described in 310.104 shall be permitted for use in any of the wiring methods covered in Chapter 3 and as specified in their respective tables or as permitted elsewhere in this Code.

Informational Note: Thermoplastic insulation may stiffen at temperatures lower than −10°C (+14°F). Thermoplastic insulation may also be deformed at normal temperatures where subjected to pressure, such as at points of support. Thermoplastic insulation, where used on dc circuits in wet locations, may result in electroendosmosis between the conductor and insulation.

(A) Dry Locations. Insulated conductors and cables used in dry locations shall be any of the types identified in this Code.

(B) Dry and Damp Locations. Insulated conductors and cables used in dry and damp locations shall be Types FEP, 70-147FEPB, MTW, PEA, RHH, RHW, RHW-2, SA, THHN, THW, THW-2, THHW, THWN, THWN-2, TW, XHH, XHHW, XHHW-2, Z, or ZW.

(C) Wet Locations. Insulated conductors and cables used in wet locations shall comply with one of the following:

  1. Be moisture-impervious metal-sheathed
  2. Be types MTW, RHW, RHW-2, TW, THW, THW-2, THHW, THWN, THWN-2, XHHW, XHHW-2, ZW
  3. Be of a type listed for use in wet locations

(D) Locations Exposed to Direct Sunlight. Insulated conductors or cables used where exposed to direct rays of the sun shall comply with (D)(1) or (D)(2):

  1. Conductors and cables shall be listed, or listed and marked, as being sunlight resistant
  2. Conductors and cables shall be covered with insulating material, such as tape or sleeving, that is listed, or listed and marked, as being sunlight resistant

(E) Shielding. Non-shielded, ozone-resistant insulated conductors with a maximum phase-to-phase voltage of 5000 volts shall be permitted in Type MC cables in industrial establishments where the conditions of maintenance and supervision ensure that only qualified persons service the installation. For other establishments, solid dielectric insulated conductors operated above 2000 volts in permanent installations shall have ozone-resistant insulation and shall be shielded. All metallic insulation shields shall be connected to a grounding electrode conductor, a grounding busbar, an equipment grounding conductor, or a grounding electrode.

Informational Note: The primary purposes of shielding are to confine the voltage stresses to the insulation, dissipate insulation leakage current, drain off the capacitive charging current, and carry ground-fault current to facilitate operation of ground-fault protective devices in the event of an electrical cable fault.

Exception No. 1: Nonshielded insulated conductors listed by a qualified testing laboratory shall be permitted for use up to 2400 volts under the following conditions:

(a) Conductors shall have insulation resistant to electric discharge and surface tracking, or the insulated conductor(s) shall be covered with a material resistant to ozone, electric discharge, and surface tracking.

(b) Where used in wet locations, the insulated conductor(s) shall have an overall nonmetallic jacket or a continuous metallic sheath.

(c) Insulation and jacket thicknesses shall be in accordance with Table 310.104(D).

Exception No. 2: Nonshielded insulated conductors listed by a qualified testing laboratory shall be permitted for use up to 5000 volts to replace existing nonshielded conductors, on existing equipment in industrial establishments only, under the following conditions:

(a) Where the condition of maintenance and supervision ensures that only qualified personnel install and service the installation.

(b) Conductors shall have insulation resistant to electric discharge and surface tracking, or the insulated conductor(s) shall be covered with a material resistant to ozone, electric discharge, and surface tracking.

(c) Where used in wet locations, the insulated conductor(s) shall have an overall nonmetallic jacket or a continuous metallic sheath.

(d) Insulation and jacket thicknesses shall be in accordance with Table 310.13(D).

Informational Note: Relocation or replacement of equipment may not comply with the term existing as related to this exception.

Exception No. 3: Where permitted in 310.10(F), Exception No. 2.

(F) Direct-Burial Conductors. Conductors used for direct-burial applications shall be of a type identified for such use.

Exception No. 1: Nonshielded multiconductor cables rated 2001-2400 volts shall be permitted if the cable has an overall metallic sheath or armor.

The metallic shield, sheath, or armor shall be connected to a grounding electrode conductor, grounding busbar, or a grounding electrode.

Exception No. 2: Airfield lighting cable used in series circuits that are rated up to 5000 volts and are powered by regulators shall be permitted to be nonshielded.

Informational Note to Exception No. 2: Federal Aviation Administration (FAA) Advisory Circulars (ACs) provide additional practices and methods for airport lighting.

Informational Note No. 1: See 300.5 for installation requirements for conductors rated 600 volts or less.

Informational Note No. 2: See 300.50 for installation requirements for conductors rated over 600 volts.

(G) Corrosive Conditions. Conductors exposed to oils, greases, vapors, gases, fumes, liquids, or other substances having a deleterious effect on the conductor or insulation shall be of a type suitable for the application.

(H) Conductors in Parallel.

(1) General. Aluminum, copper-clad aluminum, or copper conductors, for each phase, polarity, neutral, or grounded circuit shall be permitted to be connected in parallel (electrically joined at both ends) only in sizes 1/0 AWG and larger where installed in accordance with 310.10(H)(2) through (H)(6).

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Exception No. 1: Conductors in sizes smaller than 1/0 AWG shall be permitted to be run in parallel to supply control power to indicating instruments, contactors, relays, solenoids, and similar control devices, or for frequencies of 360 Hz and higher, provided all of the following apply:

(a) They are contained within the same raceway or cable.

(b) The ampacity of each individual conductor is sufficient to carry the entire load current shared by the parallel conductors.

(c) The overcurrent protection is such that the ampacity of each individual conductor will not be exceeded if one or more of the parallel conductors become inadvertently disconnected.

Exception No. 2: Under engineering supervision, 2 AWG and 1 AWG grounded neutral conductors shall he permitted to be installed in parallel for existing installations.

Informational Note to Exception No. 2: Exception No. 2 can be used to alleviate overheating of neutral conductors in existing installations due to high content of triplen harmonic currents.

(2) Conductor Characteristics. The paralleled conductors in each phase, polarity, neutral, grounded circuit conductor, equipment grounding conductor, or equipment bonding jumper shall comply with all of the following:

  1. Be the same length
  2. Consist of the same conductor material
  3. Be the same size in circular mil area
  4. Have the same insulation type
  5. Be terminated in the same manner

(3) Separate Cables or Raceways. Where run in separate cables or raceways, the cables or raceways with conductors shall have the same number of conductors and shall have the same electrical characteristics. Conductors of one phase, polarity, neutral, grounded circuit conductor, or equipment grounding conductor shall not be required to have the same physical characteristics as those of another phase, polarity, neutral, grounded circuit conductor, or equipment grounding conductor.

(4) Ampacity Adjustment. Conductors installed in parallel shall comply with the provisions of 310.15(B)(3)(a).

(5) Equipment Grounding Conductors. Where parallel equipment grounding conductors are used, they shall be sized in accordance with 250.122. Sectioned equipment grounding conductors smaller than 1/0 AWG shall be permitted in multiconductor cables in accordance with 310.104, provided the combined circular mil area of the sectioned equipment grounding conductors in each cable complies with 250.122.

(6) Equipment Bonding Jumpers. Where parallel equipment bonding jumpers are installed in raceways, they shall be sized and installed in accordance with 250.102.

310.15 Ampacities for Conductors Rated 0-2000 Volts.

(A) General.

(1) Tables or Engineering Supervision. Ampacities for conductors shall be permitted to be determined by tables as provided in 310.15(B) or under engineering supervision, as provided in 310.15(C).

Informational Note No. 1: Ampacities provided by this section do not take voltage drop into consideration. See 210.19(A), Informational Note No. 4, for branch circuits and 215.2(A), Informational Note No. 2, for feeders.

Informational Note No. 2: For the allowable ampacities of Type MTW wire, see Table 13.5.1 in NFPA 79-2007, Electrical Standard for Industrial Machinery.

(2) Selection of Ampacity. Where more than one ampacity applies for a given circuit length, the lowest value shall be used.

Exception: Where two different ampacities apply to adjacent portions of a circuit, the higher ampacity shall be permitted to be used beyond the point of transition, a distance equal to 3.0 m (10 ft) or 10 percent of the circuit length figured at the higher ampacity, whichever is less.

Informational Note: See 110.14(C) for conductor temperature limitations due to termination provisions.

(3) Temperature Limitation of Conductors. No conductor shall be used in such a manner that its operating temperature exceeds that designated for the type of insulated conductor involved. In no case shall conductors be associated together in such a way, with respect to type of circuit, the wiring method employed, or the number of conductors, that the limiting temperature of any conductor is exceeded.

Informational Note No. 1: The temperature rating of a conductor [see Table 310.104(A) and Table 310.104(C)] is the maximum temperature, at any location along its length, that the conductor can withstand over a prolonged time period without serious degradation. The allowable ampacity tables, the ampacity tables of Article 310 and the ampacity tables of Informative Annex B. the ambient temperature correction factors in 310.15(B)(2), and the notes to the tables provide guidance for coordinating conductor sizes, types, allowable ampacities, ampacities, ambient temperatures, and number of associated conductors. The principal determinants of operating temperature are as follows:

  1. Ambient temperature — ambient temperature may vary along the conductor length as well as from time to time.
  2. Heat generated internally in the conductor as the result of load current flow, including fundamental and harmonic currents. 70-149
  3. The rate at which generated heat dissipates into the ambient medium. Thermal insulation that covers or surrounds conductors affects the rate of heat dissipation.
  4. Adjacent load-carrying conductors — adjacent conductors have the dual effect of raising the ambient temperature and impeding heat dissipation.

Informational Note No. 2: Refer to 110.14(C) for the temperature limitation of terminations.

(B) Tables. Ampacities for conductors rated 0 to 2000 volts shall be as specified in the Allowable Ampacity Table 310.15(B)(16) through Table 310.15(B)(19), and Ampacity Table 310.15(B)(20) and Table 310.15(B)(21) as modified by 310.15(B)(1) through (B)(7).

The temperature correction and adjustment factors shall be permitted to be applied to the ampacity for the temperature rating of the conductor, if the corrected and adjusted ampacity does not exceed the ampacity for the temperature rating of the termination in accordance with the provisions of 110.14(C).

Informational Note: Table 310.15(B)(16) through Table 310.15(B)(19) are application tables for use in determining conductor sizes on loads calculated in accordance with Article 220. Allowable ampacities result from consideration of one or more of the following:

  1. Temperature compatibility with connected equipment, especially the connection points.
  2. Coordination with circuit and system overcurrent protection.
  3. Compliance with the requirements of product listings or certifications. See 110.3(B).
  4. Preservation of the safety benefits of established industry practices and standardized procedures.

(1) General. For explanation of type letters used in tables and for recognized sizes of conductors for the various conductor insulations, see Table 310.104(A) and Table 310.104(B). For installation requirements, see 310.1 through 310.15(A)(3) and the various articles of this Code. For flexible cords, see Table 400.4, Table 400.5(A)(1), and Table 400.5(A)(2).

(2) Ambient Temperature Correction Factors. Ampacities for ambient temperatures other than those shown in the ampacity tables shall be corrected in accordance with Table 310.15(B)(2)(a) or Table 310.15(B)(2)(b), or shall be permitted to be calculated using the following equation:

Image

where:

I′  =  ampacity corrected for ambient temperature

I   =  ampacity shown in the tables

Tc = temperature rating of conductor (°C)

Ta = new ambient temperature (°C)

Ta = ambient temperature used in the table (°C)

Table 310.15(B)(2)(a) Ambient Temperature Correction Factors Based on 30°C (86°F)
For ambient temperatures other than 30°C (86°F), multiply the allowable ampacities specified in the ampacity tables by the appropriate correction factor shown below.
Ambient Temperature (°C) Temperature Rating of Conductor Ambient Temperature (°F)
60°C 75°C 90°C
10 or less 1.29 1.20 1.15 50 or less
11–15 1.22 1.15 1.12 51–59
16–20 1.15 1.11 1.08 60–68
21–25 1.08 1.05 1.04 69–77
26–30 1.00 1.00 1.00 78–86
31–35 0.91 0.94 0.96 87–95
36–40 0.82 0.88 0.91 96–104
41–45 0.71 0.82 0.87 105–113
46–50 0.58 0.75 0.82 114–122
51–55 0.41 0.67 0.76 123–131
56–60 0.58 0.71 132–140
61–65 0.47 0.65 141–149
66–70 0.33 0.58 150–158
71–75 0.50 159–167
76–80 0.41 168–176
81–85 0.29 177–185

(3) Adjustment Factors.

(a) More Than Three Current-Carrying Conductors in a Raceway or Cable. Where the number of current-carrying conductors in a raceway or cable exceeds three, or where single conductors or multiconductor cables are installed without maintaining spacing for a continuous length longer than 600 mm (24 in.) and are not installed in raceways, the allowable ampacity of each conductor shall be reduced as shown in Table 310.15(B)(3)(a). Each current-carrying conductor of a paralleled set of conductors shall be counted as a current-carrying conductor.

Where conductors of different systems, as provided in 300.3, are installed in a common raceway or cable, the adjustment factors shown in Table 310.15(B)(3)(a) shall apply only to the number of power and lighting conductors (Articles 210, 215, 220, and 230).

Informational Note No. 1: See Annex B, Table B.310.15(B)(2)(11), for adjustment factors for more than three current-carrying conductors in a raceway or cable with load diversity.

70-150
Table 310.15(B)(2)(b) Ambient Temperature Correction Factors Based on 40°C (104°F)
For ambient temperatures other than 40°C (104°F), multiply the allowable ampacities specified in the ampacity tables by the appropriate correction factor shown below.
Ambient Temperature (°C) Temperature Rating of Conductor Ambient Temperature (°F)
60°C 75°C 90°C 150°C 200°C 250°C
10 or less 1.58 1.36 1.26 1.13 1.09 1.07 50 or less
11–15 1.50 1.31 1.22 1.11 1.08 1.06 51–59
16–20 1.41 1.25 1.18 1.09 1.06 1.05 60–68
21–25 1.32 1.2 1.14 1.07 1.05 1.04 69–77
26–30 1.22 1.13 1.10 1.04 1.03 1.02 78–86
31–35 1.12 1.07 1.05 1.02 1.02 1.01 87–95
36–40 1.00 1.00 1.00 1.00 1.00 1.00 96–104
41–45 0.87 0.93 0.95 0.98 0.98 0.99 105–113
46–50 0.71 0.85 0.89 0.95 0.97 0.98 114–122
51–55 0.50 0.76 0.84 0.93 0.95 0.96 123–131
56–60 0.65 0.77 0.90 0.94 0.95 132–140
61–65 0.53 0.71 0.88 0.92 0.94 141–149
66–70 0.38 0.63 0.85 0.90 0.93 150–158
71–75 0.55 0.83 0.88 0.91 159–167
76–80 0.45 0.80 0.87 0.90 168–176
81–90 0.74 0.83 0.87 177–194
91–100 0.67 0.79 0.85 195–212
101–110 0.60 0.75 0.82 213–230
111–120 0.52 0.71 0.79 231–248
121–130 0.43 0.66 0.76 249–266
131–140 0.30 0.61 0.72 267–284
141–160 0.50 0.65 285–320
161–180 0.35 0.58 321–356
181–200 0.49 357–392
201–225 0.35 393–437
70-151
Table 310.15(B)(3)(a) Adjustment Factors for More Than Three Current-Carrying Conductors in a Raceway or Cable
Number of Conductors1 Percent of Values in Table 310.15(B)(16) through Table 310.15(B)(19) as Adjusted for Ambient Temperature if Necessary
4–6 80
7–9 70
10–20 50
21–30 45
31–40 40
41 and above 35
1Number of conductors is the total number of conductors in the raceway or cable adjusted in accordance with 310.15(B)(5) and (6).

Informational Note No. 2: See 366.23(A) for adjustment factors for conductors in sheet metal auxiliary gutters and 376.22(B) for adjustment factors for conductors in metal wireways.

(1) Where conductors are installed in cable trays, the provisions of 392.80 shall apply.

(2) Adjustment factors shall not apply to conductors in raceways having a length not exceeding 600 mm (24 in.).

(3) Adjustment factors shall not apply to underground conductors entering or leaving an outdoor trench if those conductors have physical protection in the form of rigid metal conduit, intermediate metal conduit, rigid polyvinyl chloride conduit (PVC), or reinforced thermosetting resin conduit (RTRC) having a length not exceeding 3.05 m (10 ft), and if the number of conductors does not exceed four.

(4) Adjustment factors shall not apply to Type AC cable or to Type MC cable under the following conditions:

  1. The cables do not have an overall outer jacket.
  2. Each cable has not more than three current-carrying conductors.
  3. The conductors are 12 AWG copper.
  4. Not more than 20 current-carrying conductors are installed without maintaining spacing, are stacked, or are supported on “bridle rings.”

(5) An adjustment factor of 60 percent shall be applied to Type AC cable or Type MC cable under the following conditions:

  1. The cables do not have an overall outer jacket.
  2. The number of current carrying conductors exceeds 20.
  3. The cables are stacked or bundled longer that 600 mm (24 in) without spacing being maintained.

(b) More Than One Conduit, Tube, or Raceway. Spacing between conduits, tubing, or raceways shall be maintained.

(c) Circular Raceways Exposed to Sunlight on Rooftops. Where conductors or cables are installed in circular raceways exposed to direct sunlight on or above rooftops, the adjustments shown in Table 310.15(B)(3)(c) shall be added to the outdoor temperature to determine the applicable ambient temperature for application of the correction factors in Table 310.15(B)(2)(a) or Table 310.15(B)(2)(b).

Informational Note: One source for the average ambient temperatures in various locations is the ASHRAE Handbook — Fundamentals.

Table 310.15(B)(3)(c) Ambient Temperature Adjustment for Circular Raceways Exposed to Sunlight on or Above Rooftops
Distance Above Roof to Bottom of Conduit Temperature Adder
°C °F
0–13 mm (½ in.) 33 60
Above 13 mm (½ in.)–90 mm (3½ in.) 22 40
Above 90 mm (3½ in.)–300 mm (12 in.) 17 30
Above 300 mm (12 in.)–900 mm (36 in.) 14 25

Informational Note to Table 310.15(B)(3)(c): The temperature adders in Table 310.15(B)(3)(c) are based on the results of averaging the ambient temperatures.

(4) Bare or Covered Conductors. Where bare or covered conductors are installed with insulated conductors, the temperature rating of the bare or covered conductor shall be equal to the lowest temperature rating of the insulated conductors for the purpose of determining ampacity.

(5) Neutral Conductor.

(a) A neutral conductor that carries only the unbalanced current from other conductors of the same circuit shall not be required to be counted when applying the provisions of 310.15(B)(3)(a).

(b) In a 3-wire circuit consisting of two phase conductors and the neutral conductor of a 4-wire, 3-phase, wye-connected system, a common conductor carries approximately the same current as the line-to-neutral load currents of the other conductors and shall be counted when applying the provisions of 310.15(B)(3)(a).

(c) On a 4-wire, 3-phase wye circuit where the major portion of the load consists of nonlinear loads, harmonic currents are present in the neutral conductor; the neutral conductor shall therefore be considered a current-carrying conductor.

(6) Grounding or Bonding Conductor. A grounding or bonding conductor shall not be counted when applying the provisions of 310.15(B)(3)(a).

70-152

(7) 120/240-Volt, 3-Wire, Single-Phase Dwelling Services and Feeders. For individual dwelling units of one-family, two-family, and multifamily dwellings, conductors, as listed in Table 310.15(B)(7), shall be permitted as 120/240-volt, 3-wire, single-phase service-entrance conductors, service-lateral conductors, and feeder conductors that serve as the main power feeder to each dwelling unit and are installed in raceway or cable with or without an equipment grounding conductor. For application of this section, the main power feeder shall be the feeder between the main disconnect and the panelboard that supplies, either by branch circuits or by feeders, or both, all loads that are part or associated with the dwelling unit. The feeder conductors to a dwelling unit shall not be required to have an allowable ampacity rating greater than their service-entrance conductors. The grounded conductor shall be permitted to be smaller than the ungrounded conductors, provided the requirements of 215.2, 220.61, and 230.42 are met.

(C) Engineering Supervision. Under engineering supervision, conductor ampacities shall be permitted to be calculated by means of the following general equation:

Image

where:

Tc   =  conductor temperature in degrees Celsius (°C)

Ta   =  ambient temperature in degrees Celsius (°C)

Rdc  =  dc resistance of conductor at temperature Tc

Yc    =  component ac resistance resulting from skin effect and proximity effect

Rca  =  effective thermal resistance between conductor and surrounding ambient

Table 310.15(B)(7) Conductor Types and Sizes for 120/240-Volt, 3-Wire, Single-Phase Dwelling Services and Feeders. Conductor Types RHH, RHW, RHW-2, THHN, THHW, THW, THW-2, THWN, THWN-2, XHHW, XHHW-2, SE, USE, USE-2
Service or Feeder Rating (Amperes) Conductor (AWG or kcmil)
Copper Aluminum or Copper-Clad Aluminum
100 4 2
110 3 1
125 2 1/0
150 1 2/0
175 1/0 3/0
200 2/0 4/0
225 3/0 250
250 4/0 300
300 250 350
350 350 500
400 400 600
70-153
Table 310.15(B)(16) (formerly Table 310.16) Allowable Ampacities of Insulated Conductors Rated Up to and Including 2000 Volts, 60°C Through 90°C (140°F Through 194°F). Not More Than Three Current-Carrying Conductors in Raceway, Cable, or Earth (Directly Buried), Based on Ambient Temperature of 30°C (86°F)*
Size AWG or kcmil Temperature Rating of Conductor [See Table 310.104(A).] Size AWG or kcmil
60°C (140°F) 75°C (167°F) 90°C (194°F) 60°C (140°F) 75°C (167°F) 90°C (194°F)
Types TW, UF Types RHW, THHW, THW, THWN, XHHW, USE, ZW Types TBS, SA, SIS, FEP, FEPB, MI, RHH, RHW-2, THHN, THHW, THW-2, THWN-2, USE-2, XHH, XHHW, XHHW-2, ZW-2 Types TW, UF Types RHW, THHW, THW, THWN, XHHW, USE Types TBS, SA, SIS, THHN, THHW, THW-2, THWN-2, RHH, RHW-2, USE-2, XHH, XHHW, XHHW-2, ZW-2
  COPPER ALUMINUM OR COPPER-CLAD ALUMINUM
    18
    16
        14**
        12**
        10**
      8
    —
    —
    15
    20
    30
    40
    —
    —
    20
    25
    35
    50
    14
    18
    25
    30
    40
    55
    —
    —
    —
    15
    25
    35
    —
    —
    —
    20
    30
    40
  —
  —
  —
    25
    35
    45
  —
  —
  —
      12**
      10**
      8
      6
      4
      3
      2
      1
    55
    70
    85
    95
  110
    65
    85
  100
  115
  130
    75
    95
  115
  130
  145
    40
    55
    65
    75
    85
    50
    65
    75
    90
  100
    55
    75
    85
  100
  115
      6
      4
      3
      2
      1
   1/0
   2/0
   3/0
   4/0
  125
  145
  165
  195
  150
  175
  200
  230
  170
  195
  225
  260
  100
  115
  130
  150
  120
  135
  155
  180
  135
  150
  175
  205
   1/0
   2/0
   3/0
   4/0
  250
  300
  350
  400
  500
  215
  240
  260
  280
  320
  255
  285
  310
  335
  380
  290
  320
  350
  380
  430
  170
  195
  210
  225
  260
  205
  230
  250
  270
  310
  230
  260
  280
  305
  350
  250
  300
  350
  400
  500
  600
  700
  750
  800
  900
  350
  385
  400
  410
  435
  420
  460
  475
  490
  520
  475
  520
  535
  555
  585
  285
  315
  320
  330
  355
  340
  375
  385
  395
  425
  385
  425
  435
  445
  480
  600
  700
  750
  800
  900
1000
1250
1500
1750
2000
  455
  495
  525
  545
  555
  545
  590
  625
  650
  665
  615
  665
  705
  735
  750
  375
  405
  435
  455
  470
  445
  485
  520
  545
  560
  500
  545
  585
  615
  630
1000
1250
1500
1750
2000
*Refer to 310.15(B)(2) for the ampacity correction factors where the ambient temperature is other than 30°C (86°F).
**Refer to 240.4(D) for conductor overcurrent protection limitations.
70-154
Table 310.15(B)(17) (formerly Table 310.17) Allowable Ampacities of Single-Insulated Conductors Rated Up to and Including 2000 Volts in Free Air, Based on Ambient Temperature of 30°C (86°F)*
Size AWG or kcmil Temperature Rating of Conductor [See Table 310.104(A).] Size AWG or kcmil
60°C (140°F) 75°C (167°F) 90°C (194°F) 60°C (140°F) 75°C (167°F) 90°C (194°F)
Types TW, UF Types RHW, THHW, THW, THWN, XHHW, ZW Types TBS, SA, SIS, FEP, FEPB, MI, RHH, RHW-2, THHN, THHW, THW-2, THWN-2, USE-2, XHH, XHHW, XHHW-2, ZW-2 Types TW, UF Types RHW, THHW, THW, THWN, XHHW Types TBS, SA, SIS, THHN, THHW, THW-2, THWN-2, RHH, RHW-2, USE-2, XHH, XHHW, XHHW-2, ZW-2
  COPPER ALUMINUM OR COPPER-CLAD ALUMINUM
    18
    16
        14**
        12**
        10**
      8


    25
    30
    40
    60


    30
    35
    50
    70
    18
    24
    35
    40
    55
    80



    25
    35
    45



    30
    40
    55



    35
    45
    60



    12**
    10**
      8
      6
      4
      3
      2
      1
    80
  105
  120
  140
  165
    95
  125
  145
  170
  195
  105
  140
  165
  190
  220
    60
    80
    95
  110
  130
    75
  100
  115
  135
  155
    85
  115
  130
  150
  175
      6
      4
      3
      2
      1
   1/0
   2/0
   3/0
   4/0
  195
  225
  260
  300
  230
  265
  310
  360
  260
  300
  350
  405
  150
  175
  200
  235
  180
  210
  240
  280
  205
  235
  270
  315
   1/0
   2/0
   3/0
   4/0
  250
  300
  350
  400
  500
  340
  375
  420
  455
  515
  405
  445
  505
  545
  620
  455
  500
  570
  615
  700
  265
  290
  330
  355
  405
  315
  350
  395
  425
  485
  355
  395
  445
  480
  545
  250
  300
  350
  400
  500
  600
  700
  750
  800
  900
  575
  630
  655
  680
  730
  690
  755
  785
  815
  870
  780
  850
  885
  920
  980
  455
  500
  515
  535
  580
  545
  595
  620
  645
  700
  615
  670
  700
  725
  790
  600
  700
  750
  800
  900
1000
1250
1500
1750
2000
  780
  890
  980
1070
1155
  935
1065
1175
1280
1385
1055
1200
1325
1445
1560
  625
  710
  795
  875
  960
  750
  855
  950
1050
1150
  845
  965
1070
1185
1295
1000
1250
1500
1750
2000
*Refer to 310.15(B)(2) for the ampacity correction factors where the ambient temperature is other than 30°C (86°F).
**Refer to 240.4(D) for conductor overcurrent protection limitations.
70-155
Table 310.15(B)(18) (formerly Table 310.18) Allowable Ampacities of Insulated Conductors Rated Up to and Including 2000 Volts, 150°C Through 250°C (302°F Through 482°F). Not More Than Three Current-Carrying Conductors in Raceway or Cable, Based on Ambient Air Temperature of 40°C (104°F)*
Size AWG or kcmil Temperature Rating of Conductor [See Table 310.104(A).] Size AWG or kcmil
150°C (302°F) 200°C (392°F) 250°C (482°F) 150°C (302°F)
Type Z Types FEP, FEPB, PFA, SA Types PFAH, TFE Type Z
COPPER NICKEL OR NICKEL-COATED COPPER ALUMINUM OR COPPER-CLAD ALUMINUM
    14
    12
    10
      8
    34
    43
    55
    76
    36
    45
    60
    83
    39
    54
    73
    93

    30
    44
    57
    14
    12
    10
      8
      6
      4
      3
      2
      1
    96
  120
  143
  160
  186
  110
  125
  152
  171
  197
  117
  148
  166
  191
  215
    75
    94
  109
  124
  145
      6
      4
      3
      2
      1
   1/0
   2/0
   3/0
   4/0
  215
  251
  288
  332
  229
  260
  297
  346
  244
  273
  308
  361
  169
  198
  227
  260
   1/0
   2/0
   3/0
   4/0
*Refer to 310.15(B)(2) for the ampacity correction factors where the ambient temperature is other than 40°C (104°F).

 

Table 310.15(B)(19) (formerly Table 310.19) Allowable Ampacities of Single-Insulated Conductors, Rated Up to and Including 2000 Volts, 150°C Through 250°C (302°F Through 482°F), in Free Air, Based on Ambient Air Temperature of 40°C (104°F)*
Size AWG or kcmil Temperature Rating of Conductor [See Table 310.104(A).] Size AWG or kcmil
150°C (302°F) 200°C (392°F) 250°C (482°F) 150°C (302°F)
Type Z Types FEP, FEPB, PFA, SA Types PFAH, TFE Type Z
COPPER NICKEL OR NICKEL-COATED COPPER ALUMINUM OR COPPER-CLAD ALUMINUM
    14
    12
    10
      8
    46
    60
    80
  106
    54
    68
    90
  124
    59
    78
  107
  142

    47
    63
    83
    14
    12
    10
      8
      6
      4
      3
      2
      1
  155
  190
  214
  255
  293
  165
  220
  252
  293
  344
  205
  278
  327
  381
  440
  112
  148
  170
  198
  228
      6
      4
      3
      2
      1
   1/0
   2/0
   3/0
   4/0
  339
  390
  451
  529
  399
  467
  546
  629
  532
  591
  708
  830
  263
  305
  351
  411
   1/0
   2/0
   3/0
   4/0
*Refer to 310.15(B)(2) for the ampacity correction factors where the ambient temperature is other than 40°C (104°F).
70-156
Table 310.15(B)(20) (formerly Table 310.20) Ampacities of Not More Than Three Single Insulated Conductors, Rated Up to and Including 2000 Volts, Supported on a Messenger, Based on Ambient Air Temperature of 40°C (104°F)*
Size AWG or kcmil Temperature Rating of Conductor [See Table 310.104(A).] Size AWG or kcmil
75°C (167°F) 90°C (194°F) 75°C (167°F) 90°C (194°F)
Types RHW, THHW, THW, THWN, XHHW, ZW Types MI, THHN, THHW, THW-2, THWN-2, RHH, RHW-2, USE-2, XHHW, XHHW-2, ZW-2 Types RHW, THW, THWN, THHW, XHHW Types THHN, THHW, RHH, XHHW, RHW-2, XHHW-2, THW-2, THWN-2, USE-2, ZW-2
COPPER ALUMINUM OR COPPER-CLAD ALUMINUM
      8
      6
      4
      3
      2
      1
    57
    76
  101
  118
  135
  158
    66
    89
  117
  138
  158
  185
    44
    59
    78
    92
  106
  123
    51
    69
    91
  107
  123
  144
      8
      6
      4
      3
      2
      1
   1/0
   2/0
   3/0
   4/0
  183
  212
  245
  287
  214
  247
  287
  335
  143
  165
  192
  224
  167
  195
  224
  262
   1/0
   2/0
   3/0
   4/0
  250
  300
  350
  400
  500
  320
  359
  397
  430
  496
  374
  419
  464
  503
  580
  251
  282
  312
  339
  392
  292
  328
  364
  395
  458
  250
  300
  350
  400
  500
  600
  700
  750
  800
  900
1000
  553
  610
  638
  660
  704
  748
  647
  714
  747
  773
  826
  879
  440
  488
  512
  532
  572
  612
  514
  570
  598
  622
  669
  716
  600
  700
  750
  800
  900
1000
*Refer to 310.15(B)(2) for the ampacity correction factors where the ambient temperature is other than 40°C (104°F).

 

Table 310.15(B)(21) (formerly Table 310.21) Ampacities of Bare or Covered Conductors in Free Air, Based on 40°C (104°F) Ambient, 80°C (176°F) Total Conductor Temperature, 610 mm/sec (2 ft/sec) Wind Velocity
Copper Conductors AAC Aluminum Conductors
Bare Covered Bare Covered
AWG or kcmil Amperes AWG or kcmil Amperes AWG or kcmil Amperes AWG or kcmil Amperes
      8     98       8   103       8     76       8     80
      6   124       6   130       6     96       6   101
      4   155       4   163       4   121       4   127
      2   209       2   219       2   163       2   171
   1/0   282    1/0   297    1/0   220    1/0   231
   2/0   329    2/0   344    2/0   255    2/0   268
   3/0   382    3/0   401    3/0   297    3/0   312
   4/0   444    4/0   466    4/0   346    4/0   364
  250   494   250   519 266.8   403 266.8   423
  300   556   300   584 336.4   468 336.4   492
  500   773   500   812 397.5   522 397.5   548
  750 1000   750 1050 477.0   588 477.0   617
1000 1193 1000 1253 556.5   650 556.5   682
636.0   709 636.0   744
795.0   819 795.0   860
954.0   920
1033.5     968 1033.5 1017
1272      1103 1272    1201
1590      1267 1590    1381
2000      1454 2000    1527
70-157

310.60 Conductors Rated 2001 to 35,000 Volts.

(A) Definitions.

Electrical Ducts. As used in Article 310, electrical ducts shall include any of the electrical conduits recognized in Chapter 3 as suitable for use underground; other raceways round in cross section, listed for underground use, and embedded in earth or concrete.

Thermal Resistivity. As used in this Code, the heat transfer capability through a substance by conduction. It is the reciprocal of thermal conductivity and is designated Rho and expressed in the units °C-cm/watt.

(B) Ampacities of Conductors Rated 2001 to 35,000 Volts. Ampacities for solid dielectric-insulated conductors shall be permitted to be determined by tables or under engineering supervision, as provided in 310.60(C) and (D).

(1) Selection of Ampacity. Where more than one calculated or tabulated ampacity could apply for a given circuit length, the lowest value shall be used.

Exception: Where two different ampacities apply to adjacent portions of a circuit, the higher ampacity shall be permitted to be used beyond the point of transition, a distance equal to 3.0 m (10 ft) or 10 percent of the circuit length calculated at the higher ampacity, whichever is less.

Informational Note: See 110.40 for conductor temperature limitations due to termination provisions.

(C) Tables. Ampacities for conductors rated 2001 to 35,000 volts shall be as specified in Table 310.60(C)(67) through Table 310.60(C)(86). Ampacities for ambient temperatures other than those specified in the ampacity tables shall be corrected in accordance with 310.60(C)(4).

Informational Note No. 1: For ampacities calculated in accordance with 310.60(B), reference IEEE 835-1994 (IP-CEA Pub. No. P-46-426), Standard Power Cable Ampacity Tables, and the references therein for availability of all factors and constants.

Informational Note No. 2: Ampacities provided by this section do not take voltage drop into consideration. See 210.19(A), Informational Note No. 4, for branch circuits and 215.2(A), Informational Note No. 2, for feeders.

(1) Grounded Shields. Ampacities shown in Table 310.60(C)(69), Table 310.60(C)(70), Table 310.60(C)(81), and Table 310.60(C)(82) are for cable with shields grounded at one point only. Where shields are grounded at more than one point, ampacities shall be adjusted to take into consideration the heating due to shield currents.

(2) Burial Depth of Underground Circuits. Where the burial depth of direct burial or electrical duct bank circuits is modified from the values shown in a figure or table, ampacities shall be permitted to be modified as indicated in (C)(2)(a) and (C)(2)(b).

(a) Where burial depths are increased in part(s) of an electrical duct run, no decrease in ampacity of the conductors is needed, provided the total length of parts of the duct run increased in depth is less than 25 percent of the total run length.

(b) Where burial depths are deeper than shown in a specific underground ampacity table or figure, an ampacity derating factor of 6 percent per 300-mm (1-ft) increase in depth for all values of rho shall be permitted.

No rating change is needed where the burial depth is decreased.

(3) Electrical Ducts in Figure 310.60. At locations where electrical ducts enter equipment enclosures from underground, spacing between such ducts, as shown in Figure 310.60, shall be permitted to be reduced without requiring the ampacity of conductors therein to be reduced.

(4) Ambient Temperature Correction. Ampacities for ambient temperatures other than those specified in the ampacity tables shall be corrected in accordance with Table 310.60(C)(4)(4) or shall be permitted to be calculated using the following equation:

Image

where:

    I = ampacity corrected for ambient temperature

    I = ampacity shown in the table for Tc and Ta

 Tc = temperature rating of conductor (°C)

Ta = new ambient temperature (°C)

Ta = ambient temperature used in the table (°C)

(D) Engineering Supervision. Under engineering supervision, conductor ampacities shall be permitted to be calculated by using the following general equation:

Image

where:

  Tc = conductor temperature (°C)

  Ta = ambient temperature (°C)

Td = dielectric loss temperature rise

Rdc = dc resistance of conductor at temperature Tc

  Yc = component ac resistance resulting from skin effect and proximity effect

Rca = effective thermal resistance between conductor and surrounding ambient

Informational Note: The dielectric loss temperature rise (∆Td is negligible for single circuit extruded dielectric cables rated below 46 kV.

70-158

Figure 310.60 Cable Installation Dimensions for Use with Table 310,60(C)(77) Through Table 310.60(C)(86).

Figure 310.60 Cable Installation Dimensions for Use with Table 310.60(C)(77) Through Table 310.60(C)(86).

70-159
Table 310.60(C)(4) Ambient Temperature Correction Factors
For ambient temperatures other than 40°°C (104°F), multiply the allowable ampacities specified in the ampacity tables by the appropriate factor shown below.
Ambient Temperature (°C) Ambient Temperature Rating of Conductor Ambient Temperature (°F)
90°C 105°C
10 or less 1.26 1.21 50 or less
11–15 1.22 1.18   51–59
16–20 1.18 1.14   60–68
21–25 1.14 1.11   69–77
26–30 1.10 1.07   78–86
31–35 1.05 1.04   87–95
36–40 1.00 1.00 96–104
41–45 0.95 0.96 105–113
46–50 0.89 0.92 114–122
51–55 0.84 0.88 123–131
56–60 0.77 0.83 132–140
61–65 0.71 0.78 141–149
66–70 0.63 0.73 150–158
71–75 0.55 0.68 159–167
76–80 0.45 0.62 168–176
81–85 0.32 0.55 177–185
86–90 0.48 186–194
91–95 0.39 195–203
96–100 0.28 204–212
Table 310.60(C)(67) Ampacities of Insulated Single Copper Conductor Cables Triplexed in Air Based on Conductor Temperatures of 90°C (194°F) and 105°C (221°F) and Ambient Air Temperature of 40°C (104°F)*
  Temperature Rating of Conductor [See Table 310.104(C).]
2001–5000 Volts Ampacity 5001–35,000 Volts Ampacity
Conductor Size (AWG or kcmil) 90°C (194°F) Type MV-90 105°C (221°F) Type MV-105 90°C (194°F) Type MV-90 105°C (221°F) Type MV-105
    8
    6
    4
    2
    1
  65
  90
120
160
185
  74
  99
130
175
205

100
130
170
195

110
140
195
225
 1/0
 2/0
 3/0
 4/0
215
250
290
335
240
275
320
375
225
260
300
345
255
295
340
390
 250
 350
 500
 750
1000
375
465
580
750
880
415
515
645
835
980
380
470
580
730
850
430
525
650
820
950
*Refer to 310.60(C)(4) for the ampacity correction factors where the ambient air temperature is other than 40°C (104°F).

 

Table 310.60(C)(68) Ampacities of Insulated Single Aluminum Conductor Cables Triplexed in Air Based on Conductor Temperatures of 90°C (194°F) and 105°C (221°F) and Ambient Air Temperature of 40°C (104°F)*
  Temperature Rating of Conductor[See Table 310.104(C).]
2001–5000 Volts Ampacity 5001–35,000 Volts Ampacity
Conductor Size (AWG or kcmil) 90°C (194°F) Type MV-90 105°C (221°F) Type MV-105 90°C (194°F) Type MV-90 105°C (221°F) Type MV-105
     8
     6
     4
     2
     1
 50
 70
 90
125
145
 57
 77
100
135
160

 75
100
130
150

 84
110
150
175
 1/0
 2/0
 3/0
 4/0
170
195
225
265
185
215
250
290
175
200
230
270
200
230
265
305
250
350
500
750
1000
295
365
460
600
715
325
405
510
665
800
300
370
460
590
700
335
415
515
660
780
*Refer to 310.60(C)(4) for the ampacity correction factors where the ambient air temperature is other than 40°C(104°F)

 

Table 310.60(C)(69) Ampacities of Insulated Single Copper Conductor Isolated in Air Based on Conductor Temperatures of 90°C (194°F) and 105°C (221°F) and Ambient Air Temperature of 40°C (104°F)*
  Temperature Rating of Conductor [See Table 310.104(C).]
2001–5000 Volts Ampacity 5001–15,000 Volts Ampacity 15,001–35,000 Volts Ampacity
Conductor Size (AWG or kcmil) 90°C (194°F) Type MV-90 105°C (221°F) Type MV-105 90°C (194°F) Type MV-90 105°C (221°F) Type MV-105 90°C (194°F) Type MV-90 105°C (221°F) Type MV-105
    8
    6
    4
    2
    1
  83
110
145
190
225
  93
120
160
215
250

110
150
195
225

125
165
215
250




225




250
 1/0
 2/0
 3/0
 4/0
260
300
345
400
290
330
385
445
260
300
345
400
290
335
385
445
260
300
345
395
290
330
380
445
250
350
500
750
445
550
695
900
495
615
775
1000  
445
550
685
885
495
610
765
990
440
545
680
870
490
605
755
970
1000  
1250  
1500  
1750  
2000  
1075  
1230  
1365  
1495  
1605  
1200  
1370  
1525  
1665  
1790  
1060  
1210  
1345  
1470  
1575  
1185  
1350  
1500  
1640  
1755  
1040  
1185  
1315  
1430  
1535  
1160  
1320  
1465  
1595  
1710  
*Refer to 310.60(C)(4) for the ampacity correction factors where the ambient air temperature is other than 40°C (104°F).
70-160
Table 310.60(C)(70) Ampacities of Insulated SingleAluminum Conductor Isolated in Air Based on Conductor Temperatures of 90°C (194°F) and 105°C (221 °F) and Ambient Air Temperature of 40°C (104°F)*
  Temperature Rating of Conductor[See Table 310.104(C).]
2001–5000 Volts Ampacity 5001–15,000 Volts Ampacity 15001–35,000 Volts Ampacity
Conductor Size (AWG or kcmil) 90°C (194°F) Type MV-90 105°C (221°F) Type MV-105 90°C (194°F) Type MV-90 105°C (221°F) Type MV-105 90°C (194°F) Type MV-90 105°C (221°F) Type MV-105
    8
    6
    4
    2
    1
  64
  85
115
150
175
  71
  95
125
165
195

  87
115
150
175

  97
130
170
195




175




195
 1/0
 2/0
 3/0
 4/0
200
230
270
310
225
260
300
350
200
235
270
310
225
260
300
350
200
230
270
310
225
260
300
345
250
350
500
750
345
430
545
710
385
480
605
790
345
430
535
700
385
480
600
780
345
430
530
685
380
475
590
765
1000  
1250  
1500  
1750  
2000  
855
980
1105  
1215  
1320  
950
1095  
1230  
1355  
1475  
840
970
1085  
1195  
1295  
940
1080  
1215  
1335  
1445  
825
950
1060  
1165  
1265  
920
1055  
1180  
1300  
1410  
*Refer to 310.60(C)(4) for the ampacity correction factors where the ambient air temperature is other than 40°C (104°F).

 

Table 310.60(C)(71) Ampacities of an Insulated Three-Conductor Copper Cable Isolated in Air Based on Conductor Temperatures of 90°C (194°F) and 105°C (221°F) and Ambient Air Temperature of 40°C (104°F)*
  Temperature Rating of Conductor[See Table 310.104(C).]
2001–5000 Volts Ampacity 5001–35,000 Volts Ampacity
Conductor Size (AWG or kcmil) 90°C (194°F) Type MV-90 105°C (221°F) Type MV-105 90°C (194°F) Type MV-90 105°C (221°F) Type MV-105
     8
     6
     4
     2
     1
  59
  79
105
140
160
  66
  88
115
154
180

  93
120
165
185

105
135
185
210
 1/0
 2/0
 3/0
 4/0
185
215
250
285
205
240
280
320
215
245
285
325
240
275
315
360
250
350
500
750
1000  
320
395
485
615
705
355
440
545
685
790
360
435
535
670
770
400
490
600
745
860
*Refer to 310.60(C)(4) for the ampacity correction factors where the ambient air temperature is other than 40°C (104°F).

 

Table 310.60(C)(72) Ampacities of an Insulated Three-Conductor Aluminium Cable Isolated in Air Based on Conductor Temperatures of 90°C (194°F) and 105°C (221°F) and Ambient Air Temperature of 40°C (104°F)*
  Temperature Rating of Conductor[See Table 310.104(C).]
2001–5000 Volts Ampacity 5001–35,000 Volts Ampacity
Conductor Size (AWG or kcmil) 90°C (194°F) Type MV-90 105°C (221°F) Type MV-105 90°C (194°F) Type MV-90 105°C (221°F) Type MV-105
    8
    6
    4
    2
    1
  46
  61
  81
110
125
  51
  68
  90
120
140

  72
  95
125
145

  80
105
145
165
1/0
2/0
145
170
160
185
170
190
185
215
3/0
4/0
195
225
215
250
220
255
245
285
250
350
500
750
1000  
250
310
385
495
585
280
345
430
550
650
280
345
425
540
635
315
385
475
600
705
*Refer to 310.60(C)(4) for the ampacity correction factors where the ambient air temperature is other than 40°C (104°F).

 

Table 310.60(C)(73) Ampacities of an Insulated Triplexed or Three Single-Conductor Copper Cables in Isolated Conduit in Air Based on Conductor Temperatures of 90°C (194°F) and 105°C (221°F) and Ambient Air Temperature of 40°C (104°F)*
  Temperature Rating of Conductor[See Table 310.104(C).]
2001–5000 Volts Ampacity 5001–35,000 Volts Ampacity
Conductor Size (AWG or kcmil) 90°C (194°F) Type MV-90 105°C (221°F) Type MV-105 90°C (194°F) Type MV-90 105°C (221°F) Type MV-105
     8
     6
     4
     2
     1
  55
  75
  97
130
155
  61
  84
110
145
175

  83
110
150
170

  93
120
165
190
 1/0
 2/0
 3/0
 4/0
180
205
240
280
200
225
270
305
195
225
260
295
215
255
290
330
250
350
500
750
1000  
315
385
475
600
690
355
430
530
665
770
330
395
480
585
675
365
440
535
655
755
*Refer to 310.60(C)(4) for the ampacity correction factors where the ambient air temperature is other than 40°C (104°F).
70-161
Table 310.60(C)(74) Ampacities of an Insulated Triplexed or Three Single-Conductor Aluminium Cables in Isolated Conduit in Air Based on Conductor Temperatures of 90°C (194°F) and 105°C (221°F) and Ambient Air Temperature of 40°C (104°F)*
  Temperature Rating of Conductor[See Table 310.104(C).]
2001–5000 Volts Ampacity 5001–35,000 Volts Ampacity
Conductor Size (AWG or kcmil) 90°C (194°F) Type MV-90 105°C (221°F) Type MV-105 90°C (194°F) Type MV-90 105°C (221°F) Type MV-105
     8
     6
     4
     2
     1
  43
  58
  76
100
120
  48
  65
  85
115
135

  65
  84
115
130

  72
  94
130
150
 1/0
 2/0
 3/0
 4/0
140
160
190
215
155
175
210
240
150
175
200
230
170
200
225
260
250
350
500
750
1000  
250
305
380
490
580
280
340
425
545
645
255
310
385
485
565
290
350
430
540
640
*Refer to 310.60(C)(4) for the ampacity correction factors where the ambient air temperature is other than 40°C (104°F).

 

Table 310.60(C)(75) Ampacities of an Insulated Three-Conductor Copper Cables in Isolated Conduit in Air Based on Conductor Temperatures of 90°C (194°F) and 105°C (221°F) and Ambient Air Temperature of 40°C (104°F)*
  Temperature Rating of Conductor[See Table 310.104(C).]
2001–5000 Volts Ampacity 5001–35,000 Volts Ampacity
Conductor Size (AWG or kcmil) 90°C (194°F) Type MV-90 105°C (221°F) Type MV-105 90°C (194°F) Type MV-90 105°C (221°F) Type MV-105
     8
     6
     4
     2
     1
  52
  69
  91
125
140
  58
  77
100
135
155

  83
105
145
165

  92
120
165
185
 1/0
 2/0
 3/0
 4/0
165
190
220
255
185
210
245
285
195
220
250
290
215
245
280
320
250
350
500
750
1000  
280
350
425
525
590
315
390
475
585
660
315
385
470
570
650
350
430
525
635
725
*Refer to 310.60(C)(4) for the ampacity correction factors where the ambient air temperature is other than 40°C (104°F).

 

Table 310.60(C)(76) Ampacities of an Insulated Three-Conductor Aluminium Cables in Isolated Conduit in Air Based on Conductor Temperatures of 90°C (194°F) and 105°C (221°F) and Ambient Air Temperature of 40°C (104°F)*
  Temperature Rating of Conductor[See Table 310.104(C).]
2001–5000 Volts Ampacity 5001–35,000 Volts Ampacity
Conductor Size (AWG or kcmil) 90°C (194°F) Type MV-90 105°C (221°F) Type MV-105 90°C (194°F) Type MV-90 105°C (221°F) Type MV-105
     8
     6
     4
     2
     1
  41
  53
  71
  96
110
  46
  59
  79
105
125

  64
  84
115
130

  71
  94
125
145
 1/0
 2/0
 3/0
 4/0
130
150
170
200
145
165
190
225
150
170
195
225
170
190
220
255
250
350
500
750
1000  
220
275
340
430
505
245
305
380
480
560
250
305
380
470
550
280
340
425
520
615
*Refer to 310.60(C)(4) for the ampacity correction factors where the ambient air temperature is other than 40°C (104°F).
70-162
Table 310.60(C)(77) Ampacities of Three Single-Insulated Copper Conductors in Underground Electrical Ducts (Three Conductors per Electrical Duct) Based on Ambient Earth Temperature of 20°C (68°F), Electrical Duct Arrangement in Accordance with Figure 310.60, 100 Percent Load Factor, Thermal Resistance (RHO) of 90, Conductor Temperatures of 90°C (194°F) and 105°C (221°F)
Conductor
Size
(AWG or kcmil)
Temperature Rating of Conductor
[See Table 310.104(C).]
2001–5000 Volts
Ampacity
5001–35,000 Volts
Ampacity
90°C
(194°F)
Type
MV-90
105°C
(221°F)
Type
MV-105
90°C
(194°F)
Type
MV-90
105°C
(221°F)
Type
MV-105
One Circuit (See Figure 310.60, Detail 1.)
      8
      6
      4
      2
      1
    64
    85
  110
  145
  170
    69
    92
  120
  155
  180
   —
    90
  115
  155
  175
   —
    97
  125
  165
  185
   1/0
   2/0
   3/0
   4/0
  195
  220
  250
  290
  210
  235
  270
  310
  200
  230
  260
  295
  215
  245
  275
  315
  250
  350
  500
  750
1000
  320
  385
  470
  585
  670
  345
  415
  505
  630
  720
  325
  390
  465
  565
  640
  345
  415
  500
  610
  690
Three Circuits (See Figure 310.60, Detail 2.)
      8
      6
      4
      2
      1
    56
    73
    95
  125
  140
    60
    79
  100
  130
  150
   —
    77
    99
  130
  145
   —
    83
  105
  135
  155
   1/0
   2/0
   3/0
   4/0
  160
  185
  210
  235
  175
  195
  225
&#