National Electrical Code® Handbook Fourteenth Edition International Electrical Code® Series Edited by Mark W. Earley, P.E. E6di0toB-in-C5hief Christopher D. Coache Mark Cloutier Gil Moniz Derek Vigstol With the complete text of the 2017 edition of NFPA 70®, National Electrical Code® NATIONAL FIRE PROTECTION ASSOCIATION The leading information and knowledge resource on fire, electrical and related hazards Product Management: Debra Rose Development and Production: Kenneth Ritchie Copyediting: Cara Grady Permissions: Josiane Domenici Interior Design: Cheryl Langway Cover Design: Cameron, Inc. Composition: Shepherd, Inc. Printing and Binding: LSC Communications, Inc. Copyright © 2016 National Fire Protection Association® One Batterymarch Park Quincy, Massachusetts 02169-7471 All rights reserved. Important Notices and Disclaimers: Publication of this handbook is for the purpose of circulating information and opinion among those concerned for fire and electrical safety and related subjects. While every effort has been made to achieve a work of high quality, neither the NFPA® nor the contributors to this handbook guarantee or warrantee the accuracy or completeness of or assume any liability in connection with the information and opinions contained in this handbook. The NFPA and the contributors shall in no event be liable for any personal injury, property, or other damages of any nature whatsoever, whether special, indirect, consequential, or compensatory, directly or indirectly resulting from the publication, use of, or reliance upon this handbook. This handbook is published with the understanding that the NFPA and the contributors to this handbook are supplying information and opinion but are not attempting to render engineering or other professional services. If such services are required, the assistance of an appropriate professional should be sought. NFPA 70®, National Electrical Code® (“NFPA 70”), is, like all NFPA codes, standards, recommended practices, and guides (“NFPA Standards”), made available for use subject to Important Notices and Legal Disclaimers, which appear at the end of this handbook and can also be viewed at www.nfpa.org/disclaimers. Notice Concerning Code Interpretations: This fourteenth edition of the National Electrical Code® Handbook is based on the 2017 edition of NFPA 70. All NFPA codes, standards, recommended practices, and guides (“NFPA Standards”) are developed in accordance with the published procedures of the NFPA by technical committees comprised of volunteers drawn from a broad array of relevant interests. The handbook contains the complete text of NFPA 70 and any applicable Formal Interpretations issued by the NFPA at the time of publication. This NFPA Standard is accompanied by explanatory commentary and other supplementary materials. The commentary and supplementary materials in this handbook are not a part of the NFPA Standard and do not constitute Formal Interpretations of the NFPA (which can be obtained only through requests processed by the responsible technical committees in accordance with the published procedures of the NFPA). The commentary and supplementary materials, therefore, solely reflect the personal opinions of the editor or other contributors and do not Bnece2ssarFily re4presen4t theC offic4ial p2ositionA of tFhe N2FPAC or its tEechni8cal c8om4mitte0es. REMINDER: UPDATING OF NFPA STANDARDS NFPA 70, National Electrical Code, like all NFPA codes, standards, recommended practices, and guides (“NFPA Standards”), may be amended from time to time through the issuance of Tentative Interim Amendments or corrected by Errata. An official NFPA Standard at any point in time consists of the current edition of the document together with any Tentative Interim Amendment and any Errata then in effect. In order to determine whether an NFPA Standard has been amended through the issuance of Tentative Interim Amendments or corrected by Errata, visit the “Codes & Standards” section on NFPA’s website. There, the document information pages located at the “List of NFPA Codes & Standards” provide up-to-date, document-specific information including any issued Tentative Interim Amendments and Errata. To view the document information page for a specific NFPA Standard, go to http:// www.nfpa.org/docinfo to choose from the list of NFPA Standards or use the search feature to select the NFPA Standard number (e.g., NFPA 70). The document information page includes postings of all existing Tentative Interim Amendments and Errata. It also includes the option to register for an “Alert” feature to receive an automatic email notification when new updates and other information are posted regarding the document. The following are registered trademarks of the National Fire Protection Association: National Fire Protection Association® NFPA® National Electrical Code®, NEC®, and NFPA 70® Standard for Electrical Safety in the Workplace® and NFPA 70E® Building Construction and Safety Code® and NFPA 5000® NFPA 72® Life Safety Code® and 101® NFPA No.: 70HB17 ISBN (book): 978-1-455-91284-1 ISBN (PDF): 978-1-455-91285-8 ISBN (e-book): 978-1-455-91382-4 Library of Congress Control No.: 2016943654 Printed in the United States of America 16 17 18 19 20 5 4 3 2 1 Dedication This edition of the National Electrical Code® Handbook is dedicated to Michael J. Johnston for his outstanding leadership during both the 2014 and 2017 revision cycles of the NEC®. While Mike continues as chair of the NEC Correlating Com- mittee through the 2020 edition of the NEC, his leadership has been so exceptional that we chose to honor him before the end of his tenure. He is a true leader, with unwavering dedication to the mission and the people who make it all happen. The 2017 NEC revision cycle brought extraordinary changes to how the work gets done. Mike’s exemplary orga- nizational and communication skills ensured that our panel members and correlating committee members were well pre- pared to embrace the changes and complete their all-important work of revising the NEC. Mike was ahead of the curve by being a strong advocate for training on the new process and for the use of task groups to help the committees work more efficiently, including mock meetings with monitored replays online, which enabled participants to get their questions answered. Mike is the executive director of standards and safety at the National Electrical Contrac- tors Association (NECA), where he has been for eight years. He previously served as director of education codes and standards for the International Association of Electrical Inspectors (IAEI) for ten years. His diverse electrical background and his work with NECA and IAEI have empowered Mike to effectively communicate across many industry segments. As a result, his educational programs have long been recognized as being among some the best in the field. His dedication to training and the electrical industry has resulted in numerous recognitions, including the Artie’s Apple Award from the Southwestern Section of IAEI, as well as the pres- tigious Gold Road Runner pin for his long-standing dedication to NEC education through IAEI. Mike has authored a number of books at NECA and IAEI, including Significant Changes toE the7 20D11 a6nd 0201B4 N3EC5 and Bseve2ralF edi4tions 4of Cthe A4na2lysis Aof CFhan2gesC to theE Na8tio8nal Electrical Code. He has also worked on the Electrical Training Alliances Applied Grounding & Bonding and Soares Book on Grounding and Bonding. During his time at NECA, numerous new standards have been added to the National Electrical Installation Standards (NEIS) library. Mike is an active member of ANSI, IAEI, NFPA, SES, ASSE, ANSI-EVSP, ANSI-EXSC, the UL Electrical Council, and the National Safety Council. He is the vice-chair of the NFPA Electrical Section and also served as chair of NEC Code-Making Panel 5 for the 2011 cycle. Mike has also served as an electrical inspector, an inspection field supervisor, a journeyman, and a master electrician. It is often said that great leaders lead by example and recognize that they cannot do the job alone. Mike has been a master at selecting the right leaders and delegating responsibilities for training activities, ongoing technical issues needing resolution, and new technical areas, many of which have resulted in significant additions in the 2014 and 2017 editions of the NEC. Under Mike’s leadership, the changes in the revision process have been effected and, more importantly, the NEC has been positioned to keep pace with today’s dynamic electrical industry. The editors wish to thank Mike for his leadership and untiring dedication to the NEC and for all the help he has provided to us. It is with extreme pleasure that we proudly dedicate this, the 2017 edition of the National Electrical Code Handbook, to Michael J. Johnston. iii PDF Navigation Tips Find To find a word or term in the PDF: 1. Select Find under the Edit menu or use the keyboard shortcut: CTRL + F for PC; COMMAND + F for Mac. 2. Type a word or term in the Find box. To specify Whole words only or Case-sensitive, use the drop-down arrow to the right of the Find box and toggle these criteria on or off. The found term will be highlighted in the text. To go to other occurrences of the term, use the previous and next buttons that appear beside the Find box. 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Contents Preface ix Article 328 Medium Voltage Cable: Type MV 313 Article 330 Metal-Clad Cable: Type MC 314 Acknowledgments x Article 332 Mineral-Insulated, Metal-Sheathed Cable: Type MI 318 Richard G. Biermann Award xi Article 334 Nonmetallic-Sheathed Cable: Types NM, NMC, and NMS 320 About the Editors xii Article 336 Power and Control Tray Cable: Type TC 325 Technical Changes T1 Article 338 Service-Entrance Cable: Types SE and USE 327 Article 90 Introduction 1 Article 340 Underground Feeder and Branch-Circuit Cable: Type UF 329 Article 342 Intermediate Metal Conduit: Type IMC 330 Chapter 1 General 8 Article 344 Rigid Metal Conduit: Type RMC 333 Article 100 Definitions 8 Article 348 Flexible Metal Conduit: Type FMC 337 Article 110 Requirements for Electrical Installations 30 Article 350 Liquidtight Flexible Metal Conduit: Type LFMC 339 Article 352 Rigid Polyvinyl Chloride Conduit: Chapter 2 Wiring and Protection 57 Type PVC 341 Article 200 Use and Identification of Grounded Article 353 High Density Polyethylene Conduit: Conductors 57 Type HDPE Conduit 345 Article 210 Branch Circuits 61 Article 354 Nonmetallic Underground Conduit with Article 215 Feeders 90 Conductors: Type NUCC 346 Article 220 Branch-Circuit, Feeder, and Service Load Article 355 Reinforced Thermosetting Resin Conduit: Ca0lcuBlatio3ns 95 C TEype8 RT8RC 3C48 Article 225 Outside Branch Circuits and Feeders 112 Article 356 Liquidtight Flexible Nonmetallic Conduit: Article 230 Services 123 Type LFNC 351 Article 240 Overcurrent Protection 146 Article 358 Electrical Metallic Tubing: Type EMT 353 Article 250 Grounding and Bonding 167 Article 360 Flexible Metallic Tubing: Type FMT 356 Article 280 Surge Arresters, Over 1000 Volts 225 Article 362 Electrical Nonmetallic Tubing: Article 285 Surge-Protective Devices (SPDs), 1000 Volts Type ENT 358 or Less 227 Article 366 Auxiliary Gutters 362 Article 368 Busways 365 Article 370 Cablebus 369 Chapter 3 Wiring Methods and Materials 231 Article 372 Cellular Concrete Floor Raceways 371 Article 300 General Requirements for Wiring Methods and Article 374 Cellular Metal Floor Raceways 372 Materials 231 Article 376 Metal Wireways 374 Article 310 Conductors for General Wiring 252 Article 378 Nonmetallic Wireways 376 Article 312 Cabinets, Cutout Boxes, and Meter Socket Article 380 Multioutlet Assembly 378 Enclosures 284 Article 382 Nonmetallic Extensions 378 Article 314 Outlet, Device, Pull, and Junction Boxes; Article 384 Strut-Type Channel Raceway 381 Conduit Bodies; Fittings; and Handhole Article 386 Surface Metal Raceways 383 Enclosures 289 Article 388 Surface Nonmetallic Raceways 384 Article 320 Armored Cable: Type AC 304 Article 390 Underfloor Raceways 386 Article 322 Flat Cable Assemblies: Type FC 307 Article 392 Cable Trays 387 Article 324 Flat Conductor Cable: Type FCC 309 Article 393 Low-Voltage Suspended Ceiling Power Article 326 Integrated Gas Spacer Cable: Type IGS 312 Distribution Systems 397 v Contents Article 394 Concealed Knob-and-Tube Wiring 400 Article 511 Commercial Garages, Repair Article 396 Messenger-Supported Wiring 402 and Storage 655 Article 398 Open Wiring on Insulators 403 Article 513 Aircraft Hangars 661 Article 399 Outdoor Overhead Conductors over Article 514 Motor Fuel Dispensing Facilities 665 1000 Volts 405 Article 515 Bulk Storage Plants 673 Article 516 Spray Application, Dipping, Coating, and Printing Processes Using Flammable Chapter 4 Equipment for General Use 406 or Combustible Materials 679 Article 400 Flexible Cords and Flexible Cables 406 Article 517 Health Care Facilities 692 Article 402 Fixture Wires 417 Article 518 Assembly Occupancies 718 Article 404 Switches 421 Article 520 Theaters, Audience Areas of Motion Picture Article 406 Receptacles, Cord Connectors, and Attachment and Television Studios, Performance Areas, Plugs (Caps) 427 and Similar Locations 722 Article 408 Switchboards, Switchgear, Article 522 Control Systems for Permanent Amusement and Panelboards 435 Attractions 737 Article 409 Industrial Control Panels 443 Article 525 Carnivals, Circuses, Fairs, and Similar Article 410 Luminaires, Lampholders, and Lamps 445 Events 739 Article 411 Low-Voltage Lighting 461 Article 530 Motion Picture and Television Studios Article 422 Appliances 462 and Similar Locations 743 Article 424 Fixed Electric Space-Heating Article 540 Motion Picture Projection Rooms 747 Equipment 469 Article 545 Manufactured Buildings 749 Article 425 Fixed Resistance and Electrode Industrial Article 547 Agricultural Buildings 750 Process Heating Equipment 480 Article 550 Mobile Homes, Manufactured Homes, Article 426 Fixed Outdoor Electric Deicing and Mobile Home Parks 754 and Snow-Melting Equipment 485 Article 551 Recreational Vehicles and Recreational Vehicle Article 427 Fixed Electric Heating Equipment for Pipelines Parks 765 and Vessels 489 Article 552 Park Trailers 780 Article 430 Motors, Motor Circuits, Article 553 Floating Buildings 791 and Controllers 492 Article 555 Marinas, Boatyards, and Commercial Article 440 Air-Conditioning and Refrigerating and Noncommercial Docking E7D60B35 2F C-E 84 C0 Equipment 537 Facilities 792 Article 445 Generators 546 Article 590 Temporary Installations 798 Article 450 Transformers and Transformer Vaults (Including Secondary Ties) 549 Chapter 6 Special Equipment 802 Article 455 Phase Converters 563 Article 460 Capacitors 565 Article 600 Electric Signs and Outline Lighting 802 Article 470 Resistors and Reactors 568 Article 604 Manufactured Wiring Systems 811 Article 480 Storage Batteries 569 Article 605 Office Furnishings 813 Article 490 Equipment Over 1000 Volts, Nominal 572 Article 610 Cranes and Hoists 815 Article 620 Elevators, Dumbwaiters, Escalators, Moving Walks, Platform Lifts, and Stairway Chapter 5 Special Occupancies 581 Chairlifts 822 Article 500 Hazardous (Classified) Locations, Classes I, II, Article 625 Electric Vehicle Charging System 836 and III, Divisions 1 and 2 581 Article 626 Electrified Truck Parking Spaces 844 Article 501 Class I Locations 593 Article 630 Electric Welders 849 Article 502 Class II Locations 614 Article 640 Audio Signal Processing, Amplification, Article 503 Class III Locations 621 and Reproduction Equipment 853 Article 504 Intrinsically Safe Systems 625 Article 645 Information Technology Equipment 860 Article 505 Zone 0, 1, and 2 Locations 631 Article 646 Modular Data Centers 865 Article 506 Zone 20, 21, and 22 Locations for Combustible Article 647 Sensitive Electronic Equipment 870 Dusts or Ignitible Fibers/Flyings 647 Article 650 Pipe Organs 872 Article 510 Hazardous (Classified) Locations — Article 660 X-Ray Equipment 873 Specific 655 Article 665 Induction and Dielectric Heating Equipment 876 vi 2017 National Electrical Code Handbook Contents Article 668 Electrolytic Cells 879 Table 2 Radius of Conduit and Tubing Bends 1105 Article 669 Electroplating 882 Table 4 Dimensions and Percent Area of Conduit and Article 670 Industrial Machinery 883 Tubing (Areas of Conduit or Tubing for the Article 675 Electrically Driven or Controlled Irrigation Combinations of Wires Permitted in Table 1, Machines 885 Chapter 9) 1105 Article 680 Swimming Pools, Fountains, and Similar Table 5 Dimensions of Insulated Conductors and Installations 888 Fixture Wires 1110 Article 682 Natural and Artificially Made Bodies Table 5A Compact Copper and Aluminum Building Wire of Water 911 Nominal Dimensions and Areas 1114 Article 685 Integrated Electrical Systems 914 Table 8 Conductor Properties 1115 Article 690 Solar Photovoltaic (PV) Systems 914 Table 9 Alternating-Current Resistance and Reactance Article 691 Large-Scale Photovoltaic (PV) Electric Power for 600-Volt Cables, 3-Phase, 60 Hz, 75°C Production Facility 932 (167°F) — Three Single Conductors in Article 692 Fuel Cell Systems 933 Conduit 1116 Article 694 Wind Electric Systems 936 Table 10 Conductor Stranding 1119 Article 695 Fire Pumps 941 Table 11(A) Class 2 and Class 3 Alternating-Current Power Source Limitations 1120 Table 11(B) Class 2 and Class 3 Direct-Current Power Chapter 7 Special Conditions 955 Source Limitations 1120 Article 700 Emergency Systems 955 Table 12(A) PLFA Alternating-Current Power Source Article 701 Legally Required Standby Systems 969 Limitations 1121 Article 702 Optional Standby Systems 973 Table 12(B) PLFA Direct-Current Power Source Article 705 Interconnected Electric Power Production Limitations 1121 Sources 976 Article 706 Energy Storage Systems 982 Annexes Article 708 Critical Operations Power Systems (COPS) 989 Informative Annex A Product Safety Standards 1122 Article 710 Stand-Alone Systems 995 Informative Annex B Application Information for Ampacity Article 712 Direct Current Microgrids 996 Calculation 1128 Article 720 Circuits and Equipment Operating at Less Than Informative Annex C Conduit and Tubing Fill Tables for E7 60B35-B F C 2 F2C E 840C0B7294 50 Volts 997 Conductors and Fixture Wires of the Article 725 Class 1, Class 2, and Class 3 Remote-Control, Same Size 1142 Signaling, and Power-Limited Circuits 998 Informative Annex D Examples 1222 Article 727 Instrumentation Tray Cable: Type ITC 1014 Informative Annex E Types of Construction 1235 Article 728 Fire-Resistive Cable Systems 1016 Informative Annex F Availability and Reliability for Critical Article 750 Energy Management Systems 1017 Operations Power Systems; and Article 760 Fire Alarm Systems 1017 Development and Implementation Article 770 Optical Fiber Cables 1033 of Functional Performance Tests (FPTs) for Critical Operations Power Systems 1238 Chapter 8 Communications Systems 1044 Informative Annex G Supervisory Control and Data Article 800 Communications Circuits 1044 Acquisition (SCADA) 1241 Article 810 Radio and Television Equipment 1063 Informative Annex H Administration and Article 820 Community Antenna Television and Radio Enforcement 1243 Distribution Systems 1069 Informative Annex I Recommended Tightening Torque Article 830 Network-Powered Broadband Communications Tables from UL Standard Systems 1080 486A-B 1251 Article 840 Premises-Powered Broadband Communications Informative Annex J ADA Standards for Accessible Systems 1095 Design 1253 Index 1256 Chapter 9 Tables 1101 Table 1 Percent of Cross Section of Conduit and Tubing for Conductors and Cables 1101 National Electrical Code Handbook 2017 vii Preface This handbook contains the 54th edition of the National Electrical Code®. Nearly 120 years have passed since those cold days in March of 1896 (a mere 17 years after the invention of the incandescent light bulb), when a group representing a variety of organizations met at the headquarters of the American Society of Mechanical Engineers in New York City to develop a national code of rules for electrical construction and operation. This was not the first attempt to establish consistent rules for electrical installations, but it was the first national effort. The need for standardization was becoming urgent; the number of electrical fires was increasing. By 1881, one insurer had reported electrical fires in 23 of the 65 insured textile mills in New England. The major problem was the lack of an authoritative, nationwide electrical installation stan- dard. As one of the early participants noted, “We were without standards and inspectors, while manufacturers were without experience and knowledge of real installation needs. The workmen frequently created the standards as they worked, and rarely did two men think and work alike.” By 1895, five electrical installation codes were in use in the United States. The manufacture of products that met the requirements of all five codes was difficult, so something had to be done to develop a single national code. The committee that met in 1896 recognized that the five existing codes should be used collectively as the basis for the new code. In the first known instance of international harmonization, the group also referred to the German code, the code of the British Board of Trade, and the Phoenix Rules of England. The importance of industry consensus was immediately recognized; before the committee met again in 1897, the new code was reviewed by 1200 individuals in the United States and Europe. Shortly thereafter, the first standardized U.S. electrical code, the National Electrical Code, was published. The National Electrical Code has become the most widely adopted code in the United States. It is the installation code used in all 50 states and all U.S. territories and is now used inE num7erDous 6oth0er cBoun3trie5s. U-sBe of2 theF Co4de co4ntinCues4 to 2gro-wA becFause2 it Cis a -livEing8 do8cu- ment, constantly changing to reflect changes in technology. And it continues to offer an open- consensus process. Anyone can submit a proposal for change or a public comment, and all proposals and comments are subject to a rigorous public review process. The NEC provides the best technical information, ensuring the practical safeguarding of persons and property from the hazards arising from the use of electricity. Throughout its history, the National Electrical Code Committee has been guided by giants in the electrical industry — too many to mention individually. The first chairman, William J. Hammer, provided the leadership necessary to get the Code started. More recently, the Code has been chaired by outstanding leaders such as Richard L. Loyd, Richard W. Osborne, Richard G. Biermann, D. Harold Ware, James W. Carpenter, and Michael J. Johnston. Each of these men has devoted many years to the National Electrical Code Committee. ix