Audel Guide to the 2011 National Electrical Code E-Book

Paul Rosenberg

• Herausgeber: John Wiley & Sons
• Kategorie: Lebensstil
• Serie: Audel Technical Trades Series
• Sprache: Englisch
• Veröffentlichungsjahr: 2011

Seitenzahl: 1265

Beschreibung

The NEC is updated every 3 years with some of the anticipated changes include new requirements to sections while some of the changes include entirely new articles. Some changes are revisions to existing requirements while others are deletions to some existing requirements. As with the last edition of this book the author will use an icon or other graphical feature to highlight all changes to the 2011 code from the 2008 version. The book is considered an easy reference tool for those individuals on the job in need of a handy reference without the bulk and formality of the code itself. Significant changes to wiring and protection sections as well as new coverae of hybrid electric vehicles and small wind turbine power generators are being made. As always there will be numerous small changes made throughout the book. In short if a change has been made to the code it will be covered in this book in an easy to read instructional way.

Leseprobe

Contents

Cover

Title Page

Copyright

Foreword

Introduction

Article 90—INTRODUCTION

90.1: Purpose

90.2: Scope

90.3: Code Arrangement

90.4: Enforcement

90.5: Mandatory Rules, Permissive Rules, and Explanatory Material

90.6: Formal Interpretations

90.7: Examination of Equipment for Safety

90.8: Wiring Planning

90.9: Units of Measurement

1: General

Article 100—DEFINITIONS

Article 110—REQUIREMENTS FOR ELECTRICAL INSTALLATIONS

2: Wiring and Protection

Article 200—USE AND IDENTIFICATION OF GROUNDED CONDUCTORS

Article 210—BRANCH CIRCUITS

Article 215—FEEDERS

Article 220—BRANCH-CIRCUIT, FEEDER, AND SERVICE CALCULATIONS

Article 225—OUTSIDE BRANCH CIRCUITS AND FEEDERS

230—SERVICES

Article 240—OVERCURRENT PROTECTION

Article 250—GROUNDING

Article 280—SURGE ARRESTERS

3: Wiring Methods and Materials

Article 300—WIRING METHODS

Article 310—CONDUCTORS FOR GENERAL WIRING

Article 312—CABINETS AND CUTOUT BOXES

Article 314—OUTLET, DEVICE, PULL, AND JUNCTION BOXES, CONDUIT BODIES, FITTINGS, AND HANDHOLE ENCLOSURES

Article 320—ARMORED CABLE: TYPE AC

Article 322—FLAT CABLE ASSEMBLIES: TYPE FC

Article 324—FLAT CONDUCTOR CABLE: TYPE FCC

Article 326—INTEGRATED GAS SPACER CABLE: TYPE IGS

Article 328—MEDIUM-VOLTAGE CABLE: TYPE MV

Article 330—METAL-CLAD CABLE: TYPE MC

Article 332—MINERAL-INSULATED, METAL-SHEATHED CABLE: TYPE MI

Article 334—NONMETALLIC-SHEATHED CABLE: TYPES NM, NMC, AND NMS

Article 336—POWER AND CONTROL TRAY CABLE: TYPE TC

Article 338—SERVICE-ENTRANCE CABLE: TYPES SE AND USE

Article 340—UNDERGROUND FEEDER AND BRANCH-CIRCUIT CABLE: TYPE UF

Article 342—INTERMEDIATE METAL CONDUIT

Article 344—RIGID METAL CONDUIT

Article 348—FLEXIBLE METAL CONDUIT

Article 350—LIQUID-TIGHT FLEXIBLE METAL CONDUIT AND ARTICLE 356—LIQUID-TIGHT FLEXIBLE METAL CONDUIT

Article 352—RIGID NONMETALLIC CONDUIT—PVC

Article 353—RIGID CONDUIT—HDPE

Article 354—NONMETALLIC UNDERGROUND CONDUIT WITH CONDUCTORS

Article 355—RIGID NONMETALLIC CONDUIT—RTRC

Article 356—LIQUID-TIGHT FLEXIBLE NONMETALLIC CONDUIT

Article 358—ELECTRICAL METALLIC TUBING

Article 360—FLEXIBLE METALLIC TUBING

Article 362—ELECTRICAL NONMETALLIC TUBING

Article 366—AUXILIARY GUTTERS

Article 368—BUSWAYS

Article 370—CABLE BUS

Article 372—CELLULAR CONCRETE FLOOR RACEWAYS

Article 374—CELLULAR METAL FLOOR RACEWAYS

Article 376—METAL WIREWAYS

Article 378—NONMETALLIC WIREWAYS

Article 380—MULTIOUTLET ASSEMBLY

Article 382—NONMETALLIC EXTENSIONS

Article 386—SURFACE METAL RACEWAYS

Article 388—SURFACE NONMETALLIC RACEWAYS

Article 390—UNDERFLOOR RACEWAYS

Article 392—CABLE TRAYS

Article 394—CONCEALED KNOB-AND-TUBE WIRING

Article 396—MESSENGER-SUPPORTED WIRING

Article 398—OPEN WIRING ON INSULATORS

Article 399—OUTDOOR OVERHEAD CONDUCTORS OVER 600 VOLTS

4: Equipment for General Use

Article 400—FLEXIBLE CORDS AND CABLES

Article 402—FIXTURE WIRES

Article 404—SWITCHES

Article 406—RECEPTACLES, CORD CONNECTORS, AND ATTACHMENT PLUGS (CAPS)

Article 408—SWITCHBOARDS AND PANELBOARDS

Article 409—INDUSTRIAL CONTROL PANELS

Article 410—LIGHTING FIXTURES, LAMPHOLDERS, LAMPS, RECEPTACLES, AND ROSETTES

Article 411—LIGHTING SYSTEMS OPERATING AT 30 VOLTS OR LESS

Article 422—APPLIANCES

Article 424—FIXED ELECTRICAL SPACE-HEATING EQUIPMENT

Article 426—FIXED OUTDOOR ELECTRIC DEICING AND SNOW-MELTING EQUIPMENT

Article 427—FIXED ELECTRIC HEATING EQUIPMENT FOR PIPELINES AND VESSELS

Article 430—MOTORS, MOTOR CIRCUITS, AND CONTROLLERS

Article 440—AIR-CONDITIONING AND REFRIGERATING EQUIPMENT

Article 445—GENERATORS

Article 450—TRANSFORMERS AND TRANSFORMER VAULTS (INCLUDING SECONDARY TIES)

Article 460—CAPACITORS

Article 470—RESISTORS AND REACTORS

Article 480—STORAGE BATTERIES

Article 490—EQUIPMENT OVER 600 VOLTS, NOMINAL

5: Special Occupancies

Article 500—(CLASSIFIED) LOCATIONS

Article 501—CLASS I LOCATIONS

Article 502—CLASS II LOCATIONS

Article 503—CLASS III LOCATIONS

Article 504—INTRINSICALLY SAFE SYSTEMS

Article 505—CLASS I, ZONE 0, 1, AND 2 LOCATIONS

Article 510—HAZARDOUS (CLASSIFIED) LOCATIONS—SPECIFIC

Article 511—COMMERCIAL GARAGES, REPAIR, AND STORAGE

Article 513—AIRCRAFT HANGARS

Article 514—GASOLINE-DISPENSING AND SERVICE STATIONS

Article 515—BULK-STORAGE PLANTS

ARTICLE 516—SPRAY APPLICATION, DIPPING AND COATING PROCESSES

ARTICLE 517—HEALTH CARE FACILITIES

Article 518—ASSEMBLY OCCUPANCIES

Article 520—THEATERS AND SIMILAR LOCATIONS

Article 525—CARNIVALS, CIRCUSES, FAIRS, AND SIMILAR EVENTS

Article 530—MOTION PICTURE AND TELEVISION STUDIOS AND SIMILAR LOCATIONS

Article 540—MOTION-PICTURE PROJECTORS

Article 545—MANUFACTURED BUILDINGS

Article 547—AGRICULTURAL BUILDINGS

Article 550—MOBILE HOMES AND MOBILE HOME PARKS

Articles 551—RECREATIONAL VEHICLES AND RECREATIONAL VEHICLE PARKS

Article 553—FLOATING BUILDINGS

Article 555—MARINAS AND BOATYARDS

Article 590—TEMPORARY INSTALLATIONS

6: Special Equipment

Article 600—ELECTRIC SIGNS AND OUTLINE LIGHTING

Article 604—MANUFACTURED WIRING SYSTEMS

Article 605—OFFICE FURNISHINGS (CONSISTING OF LIGHTING ACCESSORIES AND WIRED PARTITIONS)

Article 610—CRANES AND HOISTS

Article 620—ELEVATORS, DUMBWAITERS, ESCALATORS, AND MOVING WALKS

Article 625—ELECTRIC VEHICLE CHARGING SYSTEM

Article 630—ELECTRIC WELDERS

Article 640—SOUND-RECORDING AND SIMILAR EQUIPMENT

Article 645—INFORMATION TECHNOLOGY EQUIPMENT

Article 650—ORGANS

Article 660—X-RAY EQUIPMENT

Article 665—INDUCTION AND DIELECTRIC HEATING EQUIPMENT

Article 668—ELECTROLYTIC CELLS

Article 669—ELECTROPLATING

Article 670—INDUSTRIAL MACHINERY

Article 675—ELECTRICALLY DRIVEN AND CONTROLLED IRRIGATION MACHINES

Article 680—SWIMMING POOLS, FOUNTAINS, AND SIMILAR INSTALLATIONS

Article 682—NATURAL AND ARTIFICIALLY MADE BODIES OF WATER

Article 685—INTEGRATED ELECTRICAL SYSTEMS

Article 690—SOLAR PHOTOVOLTAIC SYSTEMS

Article 692—FUEL CELL SYSTEMS

Article 695—FIRE PUMPS

7: Special Conditions

Article 700—EMERGENCY SYSTEMS

Article 701—LEGALLY REQUIRED STANDBY SYSTEMS

Article 702—OPTIONAL STANDBY SYSTEMS

Article 705—INTERCONNECTED ELECTRIC POWER PRODUCTION SOURCES

Article 708—CRITICAL OPERATIONS POWER SYSTEMS

Article 720—CIRCUITS AND EQUIPMENT OPERATING AT LESS THAN 50 VOLTS

Article 725—CLASS 1, CLASS 2, CLASS 3, AND CLASS 4 REMOTE-CONTROL, SIGNALING, AND POWER-LIMITED CIRCUITS

Article 727—INSTRUMENTATION TRAY CABLE

Article 760—FIRE-PROTECTIVE SIGNALING SYSTEMS

Article 770—OPTICAL FIBER CABLES AND RACEWAYS

8: Communications Systems

Article 800—COMMUNICATION CIRCUITS

Article 810—RADIO AND TELEVISION EQUIPMENT

Article 820—COMMUNITY ANTENNA TELEVISION AND RADIO DISTRIBUTION SYSTEMS

Article 830—NETWORK-POWERED BROADBAND COMMUNICATIONS SYSTEMS

9: Tables and Examples

Index

This book is printed on acid-free paper.

Copyright © 2011 by John Wiley & Sons, Inc. All rights reserved

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Library of Congress Cataloging-in-Publication Data:

ISBN: 978-1-118-00389-3 (pbk.); ISBN 978-1-118-02610-6 (ebk); ISBN 978-1-118-02611-3 (ebk); ISBN 978-1-118-02612-0 (ebk); ISBN 978-1-118-02613-7 (ebk); ISBN 978-1-118-02614-4 (ebk)

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; 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 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 approximately 10 to 15 persons, the majority of them engineers, and each of them sponsored by some organization, including manufacturers, industry organizations, and unions. 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, coordinate 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.

The purpose of this book is to arrange all of the pertinent requirements of the NEC in a manner that is user-friendly, allowing the reader to find the needed information painlessly and quickly. The challenge 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, the NEC is full of engineering requirements, installation requirements, and manufacturing requirements—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 applicable, a number of guides have been written, most of which have a legitimate place. These guides serve to make all parts of the NEC 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 covering everything in the NEC, we concentrated only on the requirements for electrical installations. By omitting the engineering and manufacturing requirements, much of the confusion 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 percent of the time.

This book is designed exclusively for the installer of electrical wiring, and is the result of many years of supervising and instructing 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, avoiding hassles with the local electrical inspector.

For actually installing electrical wiring, this book should be more useful than the standard NEC handbooks. For engineering questions, however, the National Electrical Code should be consulted.

Throughout this book, you will see substantive changes for the 2011 NEC highlighted. Bear in mind that these changes will have the force of law once the 2011 Code is adopted in your jurisdiction.

As you go through both this book and the Code, you will find numerous references to other codes and standards. These various codes and standards are useful but must always be used in conjunction with the NEC, not separate from it. It is critical to remember that codes are generally adopted as law by local municipalities, while standards are not. So codes contain mandatory requirements and standards contain suggested methods.

Finally, please remember that good workmanship and safety consciousness are essential ingredients for any good electrical installation. 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 installation is worthwhile.

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

*National Electrical Code® and (NEC®) are registered trademarks of the National Fire Protection Association, Inc., Quincy, MA.

Introduction

The National Electrical Code is written as a minimum standard for electrical installation for the protection of life and property. It does not necessarily define the best installation methods, merely the minimum safety standards. Many purchasers of electrical installations will want to surpass the code.

When reading and interpreting the NEC, there are certain words that you must pay attention to. These key words are:

Shall. Any time you see the word shall in the NEC, it means that you must do something a certain way. You have no choice at all; either you do it that specific way, or you are in violation of the code.

May. The word may gives you an option. You can do it the certain way that is stated, or you can do it another way; it is your choice.

Grounded Conductor. This is almost always the neutral conductor, although not necessarily. Take care not to let the word grounded confuse you; grounded conductor does not refer to a green wire.

Grounding Conductor. This is the green wire, more correctly called the equipment grounding conductor, because it is used to connect equipment to ground.

You will find these ideas expressed in section 90.5 of the NEC, discussed below. They are defined as Mandatory Rules (shall), Permissive Rules (may), and Explanatory Material (Fine Print Notes). Special care must also be taken to differentiate between similar terms, such as grounded conductor (a neutral wire), and the grounding conductor (the green equipment grounding conductor). These terms are almost identical, and if you do not carefully examine each word, you could very easily make a wrong interpretation.

In addition to these terms, there are other, less common terms (identification, listing, supervised, etc.) that can also be confusing. Remember that the NEC cannot be read casually. In order to make correct interpretations, every word must be considered. This requires extra work and effort.

Before getting to the main body of the NEC (starting with Article 100), it is important to cover the section that precedes it: Article 90 explains what the Code is and what it applies to.

Article 90—INTRODUCTION

This Article lays the groundwork for the writing and application of the National Electrical Code. It begins by stating the purpose of the document, “the practical safeguarding of persons and property from hazards arising from the use of electricity,” and goes on to explain that the NEC is written to provide safe installations, though not necessarily efficient ones.

Section 90.2 is especially important, as it identifies what sorts of installations are, or are not, covered by the NEC. Note that almost all wiring owned by utilities or mines and in boats, aircraft, and automobiles is excluded.

90.1: Purpose

1.Electricity can be dangerous if not used properly. The Code is written to provide a set of rules for the safe installation of electrical wiring.

2. This Code's provisions are those essential for safety, and compliance with these rules may not always result in the most efficient, convenient, or least expensive installations; neither does it necessarily provide for the future expansion of electrical usage. It is, however, essentially free from hazards that may be encountered. Nonconformity to the rules of the NEC may result in hazards or overloading of wiring systems. Most of these problems result from not taking into consideration the increasing usages of electricity. If future needs are taken into consideration at the time of the original installation and adequate measures are taken to provide for the increased usage of electricity, these hazards and overloading may be greatly eliminated.

3. In no manner is this Code intended to be used for design specifications or as an instruction manual for untrained persons. The rules of this Code will, however, add materially to proper design. It is also adopted as the regulations governing wiring installations by most government agencies. There may be additional requirements by the local agencies, and these should be checked out.

90.2: Scope

A.Covered. This Code covers:

1. Electric conductors and equipment installed in or on: public or private buildings or other structures, mobile homes and recreational vehicles, floating buildings, and other premises, such as yards, carnivals, parking and other lots, and industrial substations.

Additional information concerning installations in multibuilding complexes or industrial buildings is found in the National Electrical Safety Code, IEEE C2-2007.

2. The installation of conductors on the exterior of a premises is covered.

3. The installation of conductors outside of a premises is covered.

4. The installation of optical fiber cables and raceways. The inclusion of optical fiber cables in the NEC is odd, since these cables carry no electricity at all. They are included in the National Electrical Code for two primary reasons: (1) because they are usually installed by the same persons who install electrical wiring and (2) because optical fiber systems interact with, and depend upon, electrical and electronic systems.

The code's reference to optical raceway refers to special raceways whose use is dedicated to the optical cables they house. These are special inner ducts and possibly tubes associated with air-blown fiber. This is not defined clearly in the code, so check with your local inspector if you have any questions. Also, see 770.6 for details.

5. Wiring in of offices, warehouses, or other buildings owned by electric utilities but not part a generating facility, substation, or control facility.

B.Not Covered. This Code does not cover:

1. Ships, watercraft, trains, aircraft, automobiles, or trucks, although mobile homes and recreational vehicles are covered.

2. Installation of conductors is not covered in the NEC for underground mines. This does not exempt the above-ground installation of wiring, although self-propelled surface mining machinery and its trailing cables are excluded.

3. Railroad generation, transformation, and transmission or distribution, if used only for signaling devices, and railroad trains are not covered in the NEC.

4. Communication equipment located outdoors or indoors, if used exclusively by utilities, is not covered in the NEC.

5. Electric utility wiring exclusively under the utility company's control, used for communication, metering, generation, transformation, and distribution of electricity, whether indoors or outdoors on property owned or leased by the utility, whether out of doors by established rights on private property and public highways, streets, or roads, are not covered by the NEC.

6. Any metering, wiring, buildings, or structures on any premises that is not owned or leased by the utility company is covered by the NEC. The NEC does cover all wiring other than utility metering equipment ahead of service equipment through building structures or any other place not owned or leased by the utility.

C.Special Permission. Conditions and usages vary in different localities; therefore, the authority having jurisdiction for the enforcement of the Code must be able to grant exemptions for the installation of the wiring system equipment not under the control of the utilities. This occurs whenever utilities are connecting service-entrance conductors of the building or structure that they are serving. If such installations are outside the building or terminate just inside the building, special permission should be granted in writing.

There has been an abundance of work done by utilities, and often the work becomes a part of the Code. Should the installation of service laterals, for example, be deemed good engineering practice by utilities and acceptable by the enforcing authority, this practice may, by special permission, be permitted under the Code. This special permission does not eliminate the Special Permission under Article 100; it applies only to Section 90.2.

90.3: Code Arrangement

The Code is divided into an introduction and nine chapters. Chapters 1 through 4 deal with general applications of the Code to wiring and installations. Chapters 5, 6, and 7 supplement or amend the first four chapters, and deal with special occupancies and installations that involve special equipment or special conditions. Chapter 8 deals with communication circuits, and with the equipment and installation of radio and television. Chapter 9 deals with tables not included in, but to be used in conjunction with, the first eight chapters. Also included are examples for figuring requirements for installation. These examples are extremely valuable in the understanding of the preceding chapters.

Familiarity with the various Code chapters makes it easy to find what you want in the Code. Chapters 4 through 9 are special chapters and refer back to the first three chapters.

90.4: Enforcement

The NEC is written so that it can be enforced when adopted by agencies having the rights of inspection. The Code's enforcement and interpretation is placed in the hands of the enforcing agency or authority. These authorities are the ones who make the final decisions, hopefully using the good judgment that is essential in such interpretations. In many instances, the Code puts the entire responsibility of interpretation on the enforcing authority. For example, you will often find the phrase by special permission ; this means special permission, in writing, by the Code-enforcing authority.

The enforcing authority is vested with the right to decide on the approval of equipment and materials. However, listings from the Underwriters' Laboratory (UL), the Canadian Standards Association (CSA), or other independent testing laboratories are used for this purpose in many instances. One of the deterrents to Code understanding can be lack of communication between the inspector and the installer. Actually, the inspector is the installer's friend, and all the inspector wants is a good safe job. The best advice to offer in this respect is to get acquainted with your inspector; he or she will be understanding and helpful in most cases.

Many industries have established procedures for installation and maintenance that are very effective and in many cases far more safety oriented than the Code installations. This gives the enforcing authority the latitude to okay such installations.

90.5: Mandatory Rules, Permissive Rules, and Explanatory Material

The Code includes both mandatory and advisory rules. The mandatory rules are characterized by the word shall. This means that the rules must be strictly followed. Any time you see the word shall in the NEC, it means that you must do something in a certain way. You have no choice at all; either you do it that specific way, or you are in violation of the Code. Permissive rules are characterized by the word may. The word may gives you an option. You can do it the specific way that is stated, or you can do it another way; it is your choice.

Explanatory material in the NEC is placed in Informational Notes. These notes are important for you to read, but they are not enforceable.

90.6: Formal Interpretations

An NEC committee is set up to render official Code interpretations when these are necessary. In the majority of questions arising on the Code, the interpretations are under the inspector's jurisdiction, as will be seen in the next section. However, there may be instances when official interpretations are required. No official interpretations will be made unless the Formal Interpretation Procedures outlined in the Code are followed.

90.7: Examination of Equipment for Safety

Most equipment and materials have been tested by electrical testing laboratories such as UL, and carry their label. However, the rates that UL charge equipment makers can be prohibitively high. (They are somewhat of a monopoly.) To work around this problem, some municipalities have experimented with allowing consulting engineers to certify the equipment as being safe. If UL rates remain as high as they are now (or possibly go even higher), this method may become far more common. Extreme care must be taken by any inspection authority or testing service in judging the safety of any equipment, device, or material. Care must also be taken to assure that the equipment, device, and so on, will be used only in the way intended. Section 110.3 and Article 100 cover examination of equipment and the meaning of listed.

90.8: Wiring Planning

This section is unusual in that it mentions planning for future expansion, but does not require anything specific. It has long been good trade practice to oversize electrical components. However, this is not required by the NEC. Oversizing is a design issue, not an installation issue. Nonetheless, responsible installers should oversize the electrical equipment they are responsible for providing, if at all possible. Conduits should not be filled to capacity, and distribution equipment should have plenty of empty space.

In the design of electrical systems by installers, contractors, or electrical engineers, ample provision should be made in the raceways for adequate wiring, as well as distribution and load centers, which should be laid out in practical locations, keeping in mind their accessibility. The number of wires in enclosures and boxes should adhere to Code requirements in order to avoid fires and breakdowns and the inconveniences that accompany such troubles.

In reaching the goal of good wiring and installation, there is one requirement—good workmanship. Insulation damage, too many wires, and overfusing are points that must be carefully watched. Regardless of how good the design of the installation, cutting corners will defeat the intended product.

A.Future Expansion and Convenience. Since the invention of the electric light, the amounts of electricity used in both home and industry have continually increased. Therefore, in designing wiring systems consideration should be given to large enough raceways and, in some cases, spare raceways to accommodate the changes—future uses of electricity or expansion of operations—that are certain to come. During the design phase, it would be a good idea to review Sections 110.16 and 240.24, which describe the necessary clearance distances and accessibility for future additions.

B.Number of Circuits in Enclosure. You will find later in the NEC that there is a maximum number of conductors and circuits that you can put in a single enclosure such as raceways, boxes, and so on. These limitations for single raceways and boxes will reduce problems with short circuits and ground faults in a circuit.

Severe damage could be done to conductor insulation by pulling too many conductors into raceways, or by pulling around too many bends. There are even times, when pulling large sizes of conductors, that the 360 degrees in total bends between pull boxes and the like could be too many. Since the Code is not intended to be a design manual, it is up to the designer and the inspection authority to watch for these things. The Code has taken into account (derated), as you will find in Article 310, certain numbers of current-carrying conductors in raceways to avoid overheating of conductors and raceways.

90.9: Units of Measurement

Metric units, together with our own units of measurement, are used in the NEC. In the 2011 edition, metric units are set in standard text, and English units are contained in parentheses. Horsepower, wire sizes, box sizes, and conduit sizes are generally set primarily in English units.

1

GENERAL

Article 100—DEFINITIONS

The National Electrical Code (NEC) contains a great number of definitions, which are very important for interpreting the Code. If you have any doubt as to the exact meaning of a general term, 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.”

But if you need the definition of a more specific term, you may have to find it in the article where it would be dealt with most directly. As you continue through the Code, you will find additional definitions scattered throughout other articles. These definitions are usually specific to that article and are therefore included with that article 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 circuit, see Figure 100-2. For an illustration of service drop, see Figure 100-3. Service-lateral and service-entrance equipment are illustrated in Figures 100-4 and 100-5, respectively.

FIGURE 100-1 A motor circuit. The branch circuit extends from point A to point C

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

FIGURE 100-3 Illustrating the service drop attached to a building or other structure

FIGURE 100-4 Illustrating the service lateral extending from point A to point B. The service entrance is from point B to point C

FIGURE 100-5 Showing the service-entrance equipment that will serve as the electrical disconnect

Article 110—REQUIREMENTS FOR ELECTRICAL INSTALLATIONS

Article 110 is bypassed 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.

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, including special conditions. The identification, in most cases, is by labeling on the equipment.

If the preceding information is not available, it becomes the responsibility of the authority having jurisdiction to decide the suitability of the equipment.

2. The wiring material and equipment must have their parts properly designed so that the enclosure will protect other equipment.

3. Adequate splice-wire bending is required. The exact measurements are found in Tables 312.6(A) and (B) of the NEC.

4. Electrical insulation may be checked.

5. Heating effects must be taken into consideration on conductors. In Article 310, there are tables for 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.