audel guide to the 2002 national electrical code

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Audel
™
Guide to the 2002
National Electrical
Code
®
All New Edition
Paul Rosenberg
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Vice President and Executive Group Publisher: Richard Swadley
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Library of Congress Cataloging-in-Publication Data:
ISBN: 0-764-54203-6
Printed in the United States of America
10987654321
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Contents
Foreword xv
Introduction xvii
Article Chapter 1 General 1
100 Definitions 1
110 Requirements for Electrical Installations 1
General 1
600 Volts, Nominal or Less 12
Over 600 Volts, Nominal 16
Tunnel Installations Over 600 Volts, Nominal 21
Chapter 2 Wiring Design and Protection 25
200 Use and Identification of Grounded Conductors 25
210 Branch Circuits 30
General Provisions 30
Branch-Circuit Ratings 42
Required Outlets 47
215 Feeders 53
220 Branch-Circuit, Feeder, and Service Calculations 58
General 58
Feeders 61
Optional Calculations for Computing Feeder
and Service Loads 68
Method for Computing Farm Loads 72

225 Outside Branch Circuits and Feeders 73
More Than One Building or Structure 81
Over 600 Volts 85
230 Services 85
General 85
Overhead Services 89
iii
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iv Contents
Underground Service—Lateral Conductors 93
Service-Entrance Conductors 95
Service Equipment—General 103
Service Equipment—Disconnecting
Means 104
Service Equipment—Overcurrent Protection 111
Service Exceeding 600 Volts, Nominal 116
240 Overcurrent Protection 119
General 119
Location 123
Enclosures 130
Disconnecting and Guarding 130
Plug Fuses, Fuseholders, and Adapters 131
Cartridge Fuses and Fuseholders 133
Circuit Breakers 134
Supervised Industrial Installations 136
Overcurrent Protection Over 600
Volts, Nominal 137
250 Grounding 138
General 138
Circuit and System Grounding 142

Grounding Electrode System and
Grounding Electrode Conductor 156
Grounding Conductors 160
Enclosure and Raceway Grounding 168
Bonding 169
Equipment Grounding and
Equipment-Grounding Conductors 177
Methods of Equipment Grounding 183
Direct Current Systems 190
Instruments, Meters, and Relays 191
Grounding of Systems and Circuits
of 1 kV and Over (High Voltage) 193
280 Surge Arresters 195
General 195
Installation 196
Connecting Surge Arresters 196
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Chapter 3 Wiring Methods and Materials 199
300 Wiring Methods 199
General Requirements 199
Requirements for Over 600 Volts, Nominal 217
310 Conductors for General Wiring 219
312 Cabinets and Cutout Boxes 230
Installation 230
Construction Specifications 236
314 Outlet, Device, Pull, and Junction Boxes,
Conduit Bodies, and Fittings 236
General 236
Installation 237
Construction Specifications 253

Manholes and Other Electric
Enclosures Intended for Personnel Entry 255
Pull and Junction Boxes for Use on
Systems Over 600 Volts, Nominal 256
320 Armored Cable: Type AC 258
General 258
Installation 258
Construction 260
322 Flat Cable Assemblies: Type FC 261
Installation 261
Construction 262
324 Flat Conductor Cable: Type FCC 263
General 263
Installation 265
Construction 266
326 Integrated Gas Spacer Cable: Type IGS 267
328 Medium Voltage Cable: Type MV 267
330 Metal-Clad Cable: Type MC 268
General 268
Installation 268
Construction Specifications 270
332 Mineral-Insulated, Metal-Sheathed Cable:
Type MI 271
General 271
Contents v
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vi Contents
Installation 272
Construction Specifications 274
334 Nonmetallic-Sheathed Cable: Types NM

and NMC 275
General 275
Installation 276
Construction Specifications 279
336 Power and Control Tray Cable: Type TC 279
Installation 279
Construction Specifications 280
338 Service-Entrance Cable: Types SE
and USE 281
340 Underground Feeder and Branch-Circuit
Cable: Type UF 284
Installation 285
342 Intermediate Metal Conduit 286
General 286
Installation 286
Construction Specifications 289
344 Rigid Metal Conduit 289
Installation 290
Construction Specifications 294
348 Flexible Metal Conduit 295
Installation 295
Installation 298
356 Liquid-Tight Flexible Nonmetallic
Conduit 300
Installation 300
352 Rigid Nonmetallic Conduit 302
Installation 302
354 Nonmetallic Underground Conduit with
Conductors 305
General 305

Installation 306
Construction 307
358 Electrical Metallic Tubing 307
Installation 307
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360 Flexible Metallic Tubing 310
Installation 310
362 Electrical Nonmetallic Tubing 311
General 311
Installation 311
366 Auxiliary Gutters 314
368 Busways 318
General Requirements 318
Requirements for over 600 Volts, Nominal 322
370 Cablebus 324
372 Cellular Concrete Floor Raceways 326
374 Cellular Metal Floor Raceways 326
Installation 327
376 Metal Wireways 329
Installation 329
378 Nonmetallic Wireways 331
Installation 332
380 Multioutlet Assembly 333
Installation 334
382 Nonmetallic Extensions 335
Installation 335
386 Surface Metal Raceways 341
Installation 341
388 Surface Nonmetallic Raceways 343
Installation 343

Construction Specifications 344
390 Underfloor Raceways 344
392 Cable Trays 349
394 Concealed Knob-and-Tube Wiring 364
396 Messenger-Supported Wiring 367
398 Open Wiring on Insulators 369
Chapter 4 Equipment for General Use 373
400 Flexible Cords and Cables 373
General 373
Construction Specifications 377
Portable Cables Over 600 Volts, Nominal 377
Contents vii
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viii Contents
402 Fixture Wires 378
404 Switches 380
Installation 380
Construction Specifications 388
408 Switchboards and Panelboards 388
Panelboards 392
Construction Specifications 397
410 Lighting Fixtures, Lampholders, Lamps,
Receptacles, and Rosettes 397
General 397
Fixture Locations 398
Provisions at Fixture Outlet Boxes,
Canopies, and Pans 401
Fixture Supports 403
Grounding 405
Wiring of Fixtures 406

Construction of Fixtures 410
Installation of Lampholders 410
Construction of Lampholders 411
Lamps and Auxiliary Equipment 411
Receptacles, Cord Connectors, and
Attachment Plugs (Caps) 411
Special Provisions for Flush and
Recessed Fixtures 415
Construction of Flush and Recessed
Fixtures 417
Special Provisions for Electric-Discharge Lighting
Systems of 1000 Volts or Less 417
Special Provisions for Electric-Discharge Lighting
Systems of More Than 1000 Volts 420
Lighting Track 422
422 Appliances 424
General 424
Branch-Circuit Requirements 424
Installation of Appliances 425
Control and Protection of Appliances 430
Marking of Appliances 433
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424 Fixed Electrical Space-Heating Equipment 433
General 433
Installation 434
Control and Protection of Fixed Electric
Space-Heating Equipment 435
Marking of Heating Equipment 439
Electric Space-Heating Cables 440
Duct Heaters 446

Resistance-Type Boilers 447
Electrode-Type Boilers 450
Electric Radiant Heating Panels and
Heating Panel Sets 451
426 Fixed Outdoor Electric De-icing and
Snow-Melting Equipment 455
General 455
Installation 456
Resistance Heating Elements 457
Impedance Heating 460
Skin-Effect Heating 461
Control and Protection 461
427 Fixed Electric Heating Equipment for
Pipelines and Vessels 463
General 463
Installation 464
Resistance Heating Elements 465
Impedance Heating 466
Induction Heating 467
Skin-Effect Heating 467
Control and Protection 468
430 Motors, Motor Circuits, and Controllers 469
General 469
Motor Circuit Conductors 478
Motor and Branch-Circuit Overload Protection 483
Motor Branch-Circuit Short-Circuit and
Ground-Fault Protection 490
Motor Feeder Short-Circuit and
Ground-Fault Protection 495
Contents ix

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x Contents
Motor Control Circuits 497
Motor Controllers 500
Motor Control Centers 504
Disconnecting Means 505
Over 600 Volts, Nominal 510
Protection of Live Parts—All Voltages 512
Grounding All Voltages 513
440 Air-Conditioning and Refrigerating
Equipment 515
General 515
Disconnecting Means 519
Branch-Circuit, Short-Circuit, and
Ground-Fault Protection 522
Branch-Circuit Conductors 524
Controllers for Motor-Compressors 525
Motor-Compressor and Branch-Circuit
Overload Protection 526
Provisions for Room Air-Conditioners 528
445 Generators 530
450 Transformers and Transformer Vaults
(Including Secondary Ties) 532
General Provisions 533
Specific Provision Applicable to Different
Types of Transformers 545
Transformer Vaults 549
460 Capacitors 552
600 Volts, Nominal and Under 552
Over 600 Volts, Nominal 554

470 Resistors and Reactors 556
480 Storage Batteries 556
490 Equipment Over 600 Volts, Nominal 558
General 558
Equipment—Specific Provisions 560
Equipment—Metal-Enclosed Power
Switchgear and Industrial Control
Assemblies 565
Mobile and Portable Equipment 565
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Chapter 5 Special Occupancies 567
500 Hazardous (Classified) Locations 567
501 Class I Locations 576
502 Class II Locations 595
503 Class III Locations 611
504 Intrinsically Safe Systems 617
505 Class I, Zone 0, 1, and 2 Locations 620
510 Hazardous (Classified) Locations—Specific 620
511 Commercial Garages, Repair, and Storage 621
513 Aircraft Hangars 627
514 Gasoline-Dispensing and Service Stations 632
515 Bulk Storage Plants 637
516 Spray Application, Dipping, and Coating
Processes 641
517 Health Care Facilities 646
General 646
Wiring Design and Protection 651
Essential Electrical System 655
Inhalation Anesthetizing Locations 666
X-Ray Equipment 669

Communications, Signaling Systems, Data
Systems, Fire Protective Signaling Systems,
and Systems Less Than 120 Volts, Nominal 672
Isolated Power Systems 673
518 Places of Assembly 675
520 Theaters and Similar Locations 677
General 677
Fixed Stage Switchboard 678
Stage Equipment—Fixed 680
Portable Switchboards on Stage 682
Stage Equipment—Portable 683
Dressing Rooms 683
Grounding 683
527 Temporary Wiring 684
530 Motion Picture and Television Studios and
Similar Locations 687
540 Motion-Picture Projectors 687
Contents xi
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xii Contents
545 Manufactured Building 687
General 687
547 Agricultural Buildings 689
550 Mobile Homes and Mobile Home Parks 693
General 693
Mobile Homes 698
Services and Feeders 699
551 Recreational Vehicles and Recreational
Vehicle Parks 701
553 Floating Buildings 701

555 Marinas and Boatyards 701
Chapter 6 Special Equipment 703
600 Electric Signs and Outline Lighting 703
604 Manufactured Wiring Systems 703
605 Office Furnishings (Consisting of Lighting
Accessories and Wired Partitions) 704
610 Cranes and Hoists 707
620 Elevators, Dumbwaiters, Escalators, and
Moving Walks 707
630 Electric Welders 707
640 Sound-Recording and Similar Equipment 707
645 Information Technology Equipment 707
650 Organs 710
660 X-Ray Equipment 710
665 Induction and Dielectric Heating
Equipment 710
668 Electrolytic Cells 710
669 Electroplating 710
670 Industrial Machinery 710
675 Electrically Driven and Controlled
Irrigation Machines 710
680 Swimming Pools, Fountains, and Similar
Installations 711
General 711
Permanently Installed Pools 716
Storable Pools 726
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Spas and Hot Tubs 727
Fountains 729
Therapeutic Pools and Tubs in Health

Care Facilities 732
Hydromassage Bathtubs 734
685 Integrated Electrical Systems 734
General 734
Orderly Shutdown 734
690 Solar Photovoltaic Systems 735
Chapter 7 Special Conditions 737
700 Emergency Systems 737
General 737
Circuit Wiring 740
Sources of Power 741
Emergency Circuits for Lighting and Power 744
Control Emergency Lighting Circuits 745
Overcurrent Protection 746
701 Legally Required Standby Systems 746
General 746
Circuit Wiring 749
Sources of Power 749
Overcurrent Protection 749
702 Optional Standby Systems 749
General 749
Circuit Wiring 751
705 Interconnected Electric Power Production
Sources 751
720 Circuits and Equipment Operating at Less
Than 50 Volts 752
725 Class 1, Class 2, Class 3, and Class 4
Remote-Control, Signaling, and
Power-Limited Circuits 752
General 752

Class 1 Circuits 753
Class 2 and Class 3 Circuits 757
Contents xiii
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xiv Contents
760 Fire Protective Signaling Systems 759
Scope and General 759
770 Optical Fiber Cables and Raceways 760
780 Closed-Loop and Programmed Power
Distribution 764
Chapter 8 Communications Systems 765
800 Communication Circuits 765
810 Radio and Television Equipment 765
820 Community Antenna Television and Radio
Distribution Systems 765
Chapter 9 Tables and Examples 767
Annex A 767
Annex B 767
Annex C 767
Annex D 767
Index 769
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xv
Foreword
I think that almost everyone who has been required to use the
National Electrical Code
®
(NEC
®
)* on a regular basis has often

wished that it were easier to understand. Often, it seems that it
lacks sufficient clarity and detail; and other times, it seems to be
overflowing with useless information. The purpose of this book is
to help the reader sort through the voluminous code regulations
and find the information he or she needs, with a minimum of effort.
Perhaps it would help to understand where this code book comes
from.
The National Electrical Code is one of many codes and
standards that are published by the National Fire Protection
Association (NFPA), a not-for-profit corporation. The code is
revised every three years in order to keep up with new materials,
tools, and methods that are constantly being developed. This work
is performed by 21 separate committees, each consisting of approx-
imately 10 to 15 persons, the majority of them engineers. Members
of each committee meet several times, discuss all proposed changes,
accepting some and rejecting others, and rewrite (as required) the
sections of the Code that were assigned to their committee. Then,
they circulate the changes among the various committees, coordi-
nate the changes, and rewrite again. So, obviously, the updating of
the NEC is no small chore. But the real difficulty is that it must
remain applicable to all types of electrical installations, leaving no
“gaps.” Because of this, it becomes rather difficult to interpret in
many instances.
In this book, our intent is to explain each section of the code
clearly and simply. The engineers who write the code are deeply
concerned with technical accuracy and completeness. To their
credit, they generally do a very good job. But, that doesn’t ensure
that their work will be easily understood by the people who must
use the code each day. Correctness and completeness is an impor-
tant first step, but unless this complete and correct information is

understandable to the reader, it is of little practical value. That is
the only purpose of this book: to make the code’s information more
understandable and usable to the people who work with it every
day. We have endeavored to explain each section of the code in the
same way we would if we were standing on a job site.
*National Electrical Code
®
and NEC
®
are registered trademarks of the
National Fire Protection Association, Inc., Quincy, MA.
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xvi Contents
You will have to use the Guide to the 2002 National Electrical
Code in conjunction with the National Electrical Code, as the
NFPA does not permit us or anyone else to print their code.
As you go through both this book and the Code, you will find
numerous references to other codes and standards. All of these
(except as noted) are published by the NFPA, Quincy, MA, and are
available from that organization. These various codes and stan-
dards are useful but must always be used in conjunction with the
NEC, not separate from it.
My sincere thanks go to all of the fine people I’ve worked with
down through the years—I have had the good fortune of working
with some of the finest people in the industry.
Paul Rosenberg
xvi Foreword
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xvii
Introduction

Very few people who have had to work with the National Electrical
Code (NEC) would argue with the statement that it is a very diffi-
cult, complex, and confusing document. Not many professional
electricians have a thorough knowledge of it; much less the home-
owner who is trying to upgrade his or her wiring system properly.
The purpose of this book is to arrange all of the pertinent require-
ments (and only the pertinent requirements) of the National
Electrical Code in a manner that is “user-friendly,” allowing the
reader to find the needed information painlessly and very quickly.
The problem with the NEC is that many communities use it as
law, and as such, it must be written accordingly. Every possible
facet of every type of electrical installation must be covered.
Because of this, each section of the NEC is full of design criteria,
engineering requirements, installation requirements, and a host of
exceptions—all in engineering lingo and “legalese.” It’s not hard to
see why it is such a difficult document to comprehend.
In order to make the NEC more easily understood and appli-
cable, a great number of guides have been written, most of which
have a legitimate place. These guides serve to make all parts of the
Code understandable. They are written for engineers, designers,
installers, and inspectors.
The book you now hold in your hands is substantially different
from standard NEC guidebooks. Rather than seeking to write a
new guidebook covering everything in the NEC, we have elimi-
nated all of the engineering and design regulations, and concen-
trated only on the requirements for electrical installations. By
omitting the engineering and design requirements, most of the con-
fusion of the NEC is eliminated in one stroke. This leaves only the
rules that actually apply to installing electrical wiring—which is the
reason the code is referred to 99% of the time.

In addition to doing away with all of the NEC requirements that
do not pertain to installing electrical wiring, the entire text of the
book has been arranged according to the type of installation. This
way, the reader can simply turn to the appropriate section for the
type of wiring being installed, and quickly find all of the installation
requirements for the work at hand. Aside from the requirements
mentioned for each section, no other requirements should apply to
the work covered therein. All of the many electricians who have
reviewed this arrangement of installation requirements have been
enthusiastic about it.
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xviii Introduction
This book is designed exclusively for the installer of electrical
wiring, and is the result of many years of supervising and instruct-
ing electricians in the requirements of the NEC. Every effort has
been made to make this book as easy to use as possible, both for the
professional electrician and for the homeowner who wishes to do
his or her own electrical work safely and efficiently and perhaps
avoid hassles with the local electrical inspector.
For actually installing electrical wiring this book should be far
more useful than the standard NEC handbooks. For engineering
questions, however, the National Electrical Code should be
consulted.
I trust that you will find this arrangement of installation require-
ments as useful as others have. A few projects should save you more
than enough time and money to cover its expense.
Finally, please remember that good workmanship and safety-
consciousness are essential ingredients for any good electrical instal-
lation. Like fire, electricity can be the best of friends or the worst of
foes. Without careful workmanship and an overriding concern for

the safety of the installation and the installer, no electrical installa-
tion is worthwhile.
Paul Rosenberg
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Chapter 1
General
Article 100—Definitions
The National Electrical Code (NEC) contains a great number of
definitions. These are very important in interpreting the Code. If
you have any doubt as to the exact meaning of a word, it is wise to
refer to Article 100 and verify that meaning. You will also find that
the definitions in this section are arranged in two categories—
“General” and “Over 600 Volts.”
As you continue through the Code, you will find additional defi-
nitions scattered throughout other articles. These definitions are
very specific to that article and are therefore included with that arti-
cle and not in Article 100.
The following figures are useful in understanding the definitions.
For a branch circuit, see Figure 100-1. For a multiwire branch cir-
cuit, see Figure 100-2. For an illustration of service drop, see Figure
100-3. Service-lateral and service-entrance equipment are illus-
trated in Figures 100-4 and 100-5, respectively.
Article 110—Requirements for Electrical
Installations
Article 110 is by-passed in the study of the Code more often than
any other article. It is short, but it is actually the foundation upon
which the Code is written, as it contains provisions that are used
throughout the entire Code.
I. General
110.2: Approval

See definition of approved under Article 100.
1
(A) (B) (C)
TO AC
BREAKER
AT PANEL
MOTOR
STARTER
M
Figure 100-1 A motor
circuit. The branch circuit
extends from point A to
point C.
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2 Chapter 1
115V115V
PHASE A
PHASE A
PHASE B
PHASE C
PHASE B
115V115V
120V
120V
208V
208V
208V
230V
PHASE A
PHASE B

(C)
(A)
(B)
Figure 100-2 Variations of a multiwire branch circuit. Circuit C is not
a multiwire branch circuit because it utilizes two wires from the same
phase in conjunction with the neutral conductor.
SERVICE DROP
LINE POLE
METER POLE
METER
OR
SWITCH
SERVICE
ENTRANCE
Figure 100-3 Illustrating the service drop attached to a building or
other structure.
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110.3: Examination, Identification, Installation, and Use of Equipment
(A) Examination. Observe the following considerations for the
evaluation of equipment:
(1) Wiring devices and equipment that are suitable for use
must be provided with identification of the product and of
the use intended—environmental application. The identifi-
cation, in most cases, is by labeling or listing.
If the above information is not available, it becomes the
responsibility of the authority having jurisdiction to decide
the suitability of the equipment.
General 3
SERVICE LATERAL
DISTRIBUTION POLE

SERVICE EQUIPMENT
SERVICE-ENTRANCE CONDUCTORS
JUNCTION BOX
A
B
C
Figure 100-4 Illustrating the service lateral extending from point A to
point B.The service entrance is from point B to point C.
INSULATORS
METER
SERVICE-ENTRANCE
EQUIPMENT
(BREAKER OR FUSED
SWITCH OR IN SOME
CASES A DISCONNECT)
Figure 100-5 Showing the service-entrance equipment that will serve
as the electrical disconnect supply.
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4 Chapter 1
(2) The wiring material and equipment must have its parts
properly designed so that the enclosure will protect other
equipment.
(3) Adequate splice-wire bending is required. This will be
found in a table in your NEC.
(4) Electrical insulation may be checked.
(5) Heating effects must be taken into consideration on con-
ductors. In Article 310 will be found tables reducing the
ampacity of a conductor as ambient temperatures rise.
The author finds that few are familiar with high-altitude
rating of motors, which starts at 3500 feet above sea

level. In higher altitudes the air is thinner and therefore
has less cooling effect on the motor. For instance, a
5-horsepower motor at a high altitude can’t be expected
to carry as much load as the same 5-horsepower motor at
sea level.
(6) The equipment must be designed for minimal index from
arcing.
(7) The use of voltage currents must be taken into consideration.
(8) Other factors that affect safety to persons that will have
occasion to come in contact with this equipment must be
considered.
(B) Installation and Use. Labeling or listing will be effective
only if the precautions noted on the installation and use
instructions included with the labeling or listing service are
followed. Alteration of equipment in the field voids any
labeling or listing.
110.4: Voltages
The voltages referred to in the Code are the supply voltages, regard-
less of their source. The supply may be a battery, generator, trans-
former, rectifier, or a thermopile. When considering AC voltages,
the voltage is the rms voltage as explained in Article 100. There are
really three general classifications of voltages in the Code—0 to 50
volts; 50 to 600 volts; and voltages that exceed 600 volts. Each is
dealt with in separate parts of the Code. If wires having different
voltages are run in the same raceway, there are specific rules to be
followed.
No electrical equipment may be connected to a circuit that has a
voltage higher than the equipment’s rating.
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110.5: Conductors

Unless the material of which the conductor is made is specifically
identified, it is assumed to be copper. Any other material of which a
conductor may be made, such as aluminum, shall be identified as
such.
Copper and aluminum conductors have different ampacities and
are covered in Article 310. Copper-clad aluminum conductors have
the same ampacity as aluminum conductors.
110.6: Conductor Sizes
In dealing with wire sizes, the Code always refers to the American
Wire Gage (AWG). At one time, this was known as the B&S Gage.
Sizes of conductors larger than 4/0 are measured in circular mils.
110.7: Insulation Integrity
All wiring installed shall be installed free of shorts and grounds.
This does not cover potentially grounded conductors, as covered in
Article 250.
Shorts or grounds may be located before energizing circuits by
the use of a megohm-type tester (available from several manufac-
turers).
Conductors of the same circuit and in the same raceway must be
insulated with the same type of material. Therefore, insulation-
resistance tests on each conductor should produce similar values. A
case in point: Six 500 kcmil THHN conductors in the same conduit
read approximately 1500 megohms on four conductors and in the
vicinity of 300 megohms on the other two conductors. 300 megohms
would have been a good value, but the difference in the readings indi-
cated problems. The low reading cables were pulled out, and it was
found that the insulation had been cut in many places. With time and
condensation moisture, a fault would have occurred.
110.8: Wiring Method
Only recognized and suitable wiring methods are included in the

Code. Basically, Chapter 3 covers approved wiring methods; Chapters
5 through 8 cover specific conditions and occupancies.
110.9: Interrupting Rating
Interrupting capacity is far different from the rating of the amperes
that is required by a load. We are faced with what is known as fault
currents. A fault current is the amount of current that might
develop under a dead-short condition. At one time, this was not
much of a problem, but with increased electrical use and larger gen-
erating and distribution capacities, the problem of fault currents
General 5
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