How To Use The National Electrical Code

Table of Contents:
Extracted from Mike Holt's best selling book Understanding the National Electrical Code.


Attitude A certain attitude is needed to understand the NEC. There are many different types of electrical installations, but the Code could not begin to consider all of them. However, to be successful in the electrical industry, you must understand the NEC. I hope this book will excite you to learn more about the Code. I have to say that the more I learn, the more I realize how much there still is to learn. As this book progresses, you will develop some insight into these rules. Yes, there are gray areas, but generally the meaning is quite clear.

The National Electrical Code (NFPA Volume 70) has been published, edited, and revised since 1897 and has been sponsored by the National Fire Protection Association (NFPA) since 1911. The NEC is considered by some to be the finest building code standard of its kind. The NEC is used not only throughout most of the United States, but also in some other countries throughout the world, such as Mexico and Puerto Rico.

The original electrical code was developed by the combined efforts of the insurance, electrical, and architectural industries. The first electrical code was assembled by the National Association of Fire Engineers in 1897.


The National Fire Protection Association (NFPA) has many other standards besides the NEC that are related to the electrical field. The NFPA standards (including the NEC) are in effect only if the legal jurisdictions have adopted them as law.

The twenty NFPA Code Panels responsible for the NEC often consult with the technical experts and members responsible for other NFPA standards. The NEC rules should correlate with the regulations in other NFPA standards.

Code Changes

Anyone may suggest a change to the National Electrical Code by submitting a proposal to the National Fire Protection Association. If you would like to submit a code change to the 1999 NEC, be sure to submit it no later than November 1999. When submitting changes, keep in mind that the primary purpose of the NEC is the protection of life and property. At the front of the NEC there are detailed instructions on how to submit a code change.

Why is the NEC so hard to figure out?


Learning to use the NEC is like learning to play the game of chess. If you have never played chess, you will need to learn the terms used to identify the game pieces, the theory of how each piece moves and how the pieces are set up on the board. Once you have this basic understanding of the game, you may start to play the game; but all you can do is make crude moves because you don't completely understand how the pieces work together.

To play the game well, you need to study the rules, understand the subtle and complicated strategies, and then practice, practice and more practice.

Learning the terms, theory, and layout of the NEC gives you just enough knowledge to be dangerous. The hard part is understanding how all the parts work together. Perhaps the most difficult part is the subtle meanings in the Code rules themselves.

The rules in the NEC are not as simple as we would want them to be. There are thousands of different applications of electrical installations and there cannot be a specific Code rule for every application. You must learn the purpose of the NEC and then use common sense when you applying the rule. Please don't get so caught up with the rule, that you forget to use common sense.

This book is designed to help you with electrical terms, theories, and how to understand the NEC rules. A companion workbook that contains over 1,000 questions is available to give you the practice you need on how to use the NEC.

Understanding Terms and Theory


There are many technical words and phrases used in the NEC. It is crucial that you understand the meanings of words like ground, grounded, grounding, and neutral. If you do not clearly understand the terms used in the Code, you will not understand the rule itself.

It isn't always the technical words that require close attention. In the NEC, even the simplest words can make a big difference. The word "or" can mean an alternate choices for equipment, wiring methods, or other requirements. Sometimes, the word "or" can mean any item in a group. The word "and" can mean an additional requirement or any item in a group. Be aware of how simple words are used.

Electricians, engineers, and other trade-related professionals have created their own terms and phrases. This is what we call slang. One of the problems with a slang terms is that they mean different things to different people and they are not used in the NEC. Example, the words sub-feeder and bond wire. The proper names associated with most slang terms have been identified. This book should help you understand the proper terms so that you no longer need to use the slang terms.


Theory is simply understanding how and why things work the way they do. Why can a bird sit on an energized power line without getting shocked? Why does installing a lot of wires close together reduce the amount of current they can individually carry? Why can't a single conductor be installed in a metal raceway? Why can the circuit breaker to a motor circuit be 40 amperes, when the conductors are only rated 20 amperes? Why can't a 20-ampere receptacle be installed on a 15-ampere circuit? If you understand why or how things work you will probably understand the Code rules.

Layout of the NEC

Contrary to popular belief, the NEC is a fairly well organized document, although parts of it are somewhat vague. Understanding the NEC structure and writing style is extremely important to understand and use the Code book effectively. The National Electrical Code is organized into 12 components.

  1. Chapters (major categories)
  2. Articles (individual subjects)
  3. Parts (divisions of an Article)
  4. Sections, Lists, and Tables (Code rules)
  5. Exceptions (Code rules)
  6. Fine Print Notes (explanatory material, not mandatory Code language)
  7. Definitions (Code rules)
  8. Superscript Letter X
  9. Marginal Notations, Code changes (|) and deletions (bullet)
  10. Table of Contents
  11. Index
  12. Appendices

A short description of each component follows:

1. Chapters.

There are nine chapters in the NEC. Each chapter is a group of articles, parts, sections, and tables. The nine chapters fall into four categories:

Chapters 1 through 4: General Rules

Chapters 5 through 7: Specific Rules (Motion Picture Projectors, Recreational Vehicles, Cranes and Hoists, X-Ray Equipment, etc.)

Chapter 8: Communication Systems (Radio and Television Equipment and Cable TV Systems)

Chapter 9: Physical Properties and NEC Examples (Tables for conductor and raceways)

2. Articles.

The NEC contains approximately 125 articles. An article is a specific subject, such as:

  1. Article 110 - General Requirements
  2. Article 250 - Grounding
  3. Article 300 - Wiring Methods
  4. Article 430 - Motors
  5. Article 500 - Hazardous (classified) Locations
  6. Article 680 - Swimming Pools
  7. Article 725 - Control Wiring
  8. Article 800 - Communication Wiring


3. Parts.

When an article is sufficiently large, the article is subdivided into parts. The parts break down the main subject of the article into organized groups of information. For example Article 250 contains nine parts, such as:

  1. Part A-General
  2. Part B-Circuit and System Grounding
  3. Part C-Grounding Electrode System


Caution The "Parts" of a Code Article are not included in the Section numbers. Because of this, we have a tendency to forget what "Part" the Code rule is relating to. For example, Table 110-34 gives the dimensions of working space clearances in front of electrical equipment. If we are not careful, we might think that this table applies to all electrical installations. But Section 110-34 is located in Part C Over-600 volt Systems of Article 110! The working clearance rule for under-600 volt systems is located in Part A of Article 110, in Table 110-26.

4. Sections, Lists, and Tables (Code rules).

Section - Each actual Code rule is called a Section and is identified with numbers, such as Section 225-26. A Code Section may be broken down into subsections by letters in parentheses, and numbers in parentheses may further break down each subsection. For example, the rule that requires all receptacles in a bathroom to be GFCI protected is contained in Section 210-8(a)(1).

Note: Note. Many in the electrical industry incorrectly use the term "Article"" when referring to a Code Section.

List - The 1999 NEC has changed the layout of some Sections that contain lists of items. If a list is part of a numeric subsection, such as Section 210-52(a)(2), then the items are listed as a., b., c., etc. However, if a list is part of a Section, then the items are identified as (1), (2), (3), (4), etc.

Tables - Tables. Many Code requirements are contained within Tables which are a systematic list of Code rules in an orderly arrangement. For example, Table 300-15 lists the burial depths of cables and raceways.

5. Exceptions.

Exceptions are italicized and provide an alternative to a specific rule. There are two types of exceptions: mandatory and permissive. When a rule has several exceptions, those exceptions with mandatory requirements are listed before those written in permissive language.

(a) Mandatory Exception. A mandatory exception uses the words "shall" or "shall not." The word "shall" in an exception means that if you are using the exception, you are required to do it in a particular way. The term "shall not" means that you cannot do something.

(b) Permissive Exception. A permissive exception uses such words as "shall be permitted", which means that it is accepted to do it in this way.

6. Fine Print Notes.

Fine Print Notes (FPN) are explanatory material, not Code rules. Fine print notes attempt to clarify a rule or give assistance, but they are not a Code requirement. For example, FPN No. 4 of Section 210-19(a) states that the voltage drop for branch circuits should not exceed 3% of the circuit voltage. This is not a Code requirement but only a suggestion; there is no NEC requirement for conductor voltage drop.

7. Definitions.

Definitions are listed in Article 100 and throughout the NEC. In general, the definitions listed in Article 100 apply to more than one Code Article, such as "branch circuit", which is used in many Articles.

Definitions at the beginning of a specific Article applies only to that Article. For example, the definition of a "Swimming Pool" is contained in Section 680-4 because this term applies only to the requirements of Article 680 - Swimming Pools.

Definitions located in a Part of an Article apply only to that Part of the Article. For example, the definition of "motor control circuit" applies only to Article 430, Part F.

Definitions located in a Code Section apply only to that Code Section. For example, the definition of "Festoon Lighting" located in Section 225-6(b) applies only to the requirements contained in Section 225-6.

8. Superscript Letter x.

This superscript letter is used only in Chapter 5. The superscript letter X means the material was extracted from other NFPA documents. Appendix A, at the back of the Code Book, identifies the NFPA document and the section(s) that the material was extracted from.

9. Changes and Deletions.

Changes and deletions to the 1996 NEC are identified in the margins of the 1999 NEC in the following manner: Changes are marked with a vertical line (|) and deletions of a Code rule are identified by a bullet.

10. Table of Contents.

The Table of Contents located in the front of the Code book displays the layout of the Chapters, Articles, and Parts as well as their location in the Code book.

11. Index.

We all know the purpose of an index, but it's not that easy to use. You really need to know the correct term. Often it's much easier to use the Table of Contents.

12. Appendices.

There are four appendices in the 1999 NEC:

Appendix A - Extract Information
Appendix B - Ampacity Engineering Supervision
Appendix C - Conduit and Tubing Fill Tables
Appendix D - Electrical Calculation Examples

How to use the NEC

How fast you find things in the NEC depends on your experience. Experienced Code users often use the Table of Contents instead of the index.

For example, what Code rule indicates the maximum number of disconnects permitted for a service?

Answer. You need to know that Article 230 is for Services and that it contains a Part F. Disconnection Means. If you know this, using the Table of Contents, you'll see that the answer is contained at page 66.

People frequently use the index which lists subjects in alphabetical order. It's usually the best place to start for specific information. Unlike most books, the NEC index does not list page numbers; it lists Sections, Tables, Articles, parts, and appendices by their Section number.

Note. Many people say the Code takes them in circles, and sometimes it does. However, this complaint is often heard from inexperienced persons who don't understand electrical theory, electrical terms, and electrical practices.

Different Interpretations

Anytime there is more than one electrical person in the same room, they will argue Code. When people have a difference of opinion, it's often because one is talking about one point and the other is talking about another, or simply they don't know what they're talking about.

Electricians, contractors, some inspectors, and others love arguing Code interpretations and discussing Code requirements. Discussing the Code and its application with others is a great way to increase your knowledge of the NEC and how it can be used.

I have taken great care in researching the Code rules in this book. But I'm not perfect. If you disagree with my comments, please feel free to contact me personally. I enjoy discussing Code just as much as the next guy. I hope you learn that when you argue a Code rule, you use the specific Code section(s) and you don't just throw words into the conversation.

Note. At times in this book I have supported my comments by referring to The National Electrical Code Committee Report on Proposals [ROP], and at times to The National Electrical Code Committee Report on Comments [ROC]. This document is available from the NFPA by contacting them directly.

Warning: Understanding and knowing the Code can cause people to go around showing their co-workers how brilliant they are (I know I did). If you are going to explain the Code, please do it in a positive way and be constructive with your comments. If you know more about the Code than your supervisor or inspector (and everyone thinks he or she does), be careful how you explain your position. Attitude is everything.


Customizing your Code Book

One way for you to get comfortable with your Code book is to customize it to meet your needs. This you can do by highlighting, underlining Code rules, and using convenient tabs.

Highlighting and Underlining. As you read through this book, highlight in the NEC book those Code rules that are important to you such as yellow for general interest, and orange for rules you want to find quickly. As you use the Index and the Table of Contents, highlight terms in those areas as well. Underline or circle key words and phrases in the NEC with a red pen (not a lead pencil) and use a 6 inch ruler to keep lines straight and neat.

Because of the new format of the 1999 NEC (81/2 x 11), I highly recommend that you highlight in green the Parts of at least the following Articles.
Article 230 - Services
Article 250 - Grounding
Article 410 - Fixtures
Article 430 - Motors

Tabbing the NEC. Tabbing the NEC permits you to quickly access Code Article, Section, or Tables. However, too many tabs will defeat the purpose.

Experience has shown that the best way to tab the Code book is to start by placing the last tab first and the first tab last (start at the back of the book and work your way toward the front). Install the first tab, then place each following tab so that they do not overlap the information of the previous tab.

The following is a list of Articles and Sections I most commonly refer to. Place a tab only on the Section s or Articles that are important to you.
1 Index, Page 621
2 Examples: Appendix D, Page 609
3 Raceway Fill Tables: Appendix C, Page 585
4 Conductor Area: Table 5 of Chapter 9, Page 564
5 Raceway Area: Table 4 of Chapter 9, Page 562
6 Satellites and Antennas: Article 820, Page 545
7 Communication: Article 800, Page 533
8 Fiber Optic Cables: Article 770, Page 527
9 Fire Alarms: Article 760, Page 519
10 Control Circuits: Article 725, Page 510
11 Emergency Circuits: Article 700, Page 501
12 Pools, Spas and Fountains: Article 680, Page 476
13 Electric Signs: Article 600, Page 433
14 Marinas: Article 555, Page 431
15 Mobile/Manufactured: Article 550, Page 398
16 Carnivals, Circuses, and Fairs: Article 525, Page 387
17 Health Care Facilities: Article 517, Page 359
18 Gasoline Dispensers: Article 514, Page 346
19 Hazardous Locations: Article 500, Page 309
20 Transformers: Article 450, Page 290 22 Air-Conditioning: Article 440, Page 283
23 Motors: Article 430, Page 256
24 Electric Space Heating: Article 424, Page 241
25 Appliances: Article 422, Page 236
26 Lighting Fixtures: Article 410, Page 225
27 Cords: Article 400, Page 211
28 Panelboards: Article 384, Page 207
29 Switches: Article 380, Page 204
30 Outlet and Junction Boxes: Article 370, Page 191
31 Flexible Metal Conduit: Article 350, Page 175
32 Electrical Metallic Tubing: Article 348, Page 172
33 Rigid Nonmetallic Conduit: Article 347, Page 169
34 Nonmetallic-Sheathed Cable: Article 336, Page 159
35 Electrical Nonmetallic Tubing: Article 331, Page 154
36 Cable Trays: Article 318, Page 140
37 Conductor Ampacity: Table 310-16 , Page 126
38 Wiring Methods: Article 300, Page 105
39 Grounding and Bonding: Article 250, Page 80
40 Overcurrent Protection: Article 240, Page 70
41 Services: Article 230, Page 61
42 Outside Feeder/Branch Circuit: Article 225, Page 55
43 Service/Feeder Calculations: Article 220, Page 48
44 Feeders: Article 215, Page 46
45 Branch Circuits: Article 210, Page 37
46 General Requirements: Article 110, Page 26
47 Definitions: Article 100, Page 19
48 Table of Contents, Page 2

National Electrical Code (NFPA 70)

Article 90 is the Introduction to the National Electrical Code. As with most introductions, this article is often skipped. To understand the NEC and its application better, it is very important that you thoroughly read and review this article.

Article 90 - Introduction

90-1 Purpose

(a) Practical Safeguarding. The purpose of the NEC is the protection of persons and property by minimizing the risks caused by the use of electricity, Fig. 1-1.

(b) Adequacy. The Code is intended for the application of safety. When the rules of the NEC are complied with, an installation is expected to be essentially free from hazards. However, when installations comply with the NEC, this does not mean that the electrical system will be efficient, convenient, adequate for good service, or that it will work properly.

(FPN, Fine Print Note) Hazards can occur because of overloading of circuits and improper installation of equipment. These problems often arise because the original installation did not provide for future expansion, which is not required by the Code.

Caution: The NEC does not contain any rule that requires consideration for future expansion of electrical use. The NEC is concerned solely with safety; but the electrical designer must be concerned with safety, efficiency, convenience, good service, and future expansion. Often, electrical systems are designed and installed that exceed NEC requirements. However, the inspector does not have the authority to require installations to exceed the NEC requirements, unless additional requirements have been adopted by local ordinance.

(b) Intention. The Code is not a how-to book; it is not intended as a design specification or an instruction manual for untrained persons.

90-2 Scope

The National Electrical Code is not intended to apply to all electrical installations. Sub-section (a) explains what is covered and sub-section (b) explains what is not covered by the NEC.

(a) Covered. The Code covers most electrical installations, including most buildings, mobile homes, recreational vehicles, floating buildings, yards, carnivals, parking and other lots, and private industrial substations. Also covered are conductors and equipment that connect to the supply of electricity, conductors and equipment outside on the premises, and the installation of fiber optic cable.

Installation within buildings 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 must be installed in accordance with the NEC.

(b) Not Covered. The Code does not cover:

  1. (1) Installations in cars, trucks, boats, ships, planes, electric trains, or underground mines.
  2. (2) Self-propelled mobile surface mining machinery and their attendant electrical trailing cable.
  3. (3) Railway power, signaling and communications wiring.
  4. (4) Communications equipment under the exclusive control of a communication utility, such as telephone and cable TV companies, are covered by their own wiring and equipment rules and are not required to comply with the NEC. However, the interior and exterior wiring of phone, communications, and CATV not under the exclusive control of communication utilities must comply with NEC Chapter 8.
  5. (5) Installations, including associated lighting, under the exclusive control of electric utilities for the purpose of power generation, distribution, control, transformation, and transmission are not required to comply with the NEC. This includes installations located in buildings used exclusively by utilities for such purposes, outdoors on property owned or leased by the utility, or on public highways, streets, roads, etc., or outdoors on private property by established rights such as easements.

Note. Any wiring installation such as lighting fixtures on private property without established rights (such as easements) and not intended for the purpose of communications, metering, generation, control, transformation, transmission, and distribution of electric energy, must be installed according to the NEC requirements, even if installed by the electric utility, Fig. 1-3.

90-3 Code Arrangement

The Code is divided into the Introduction and nine chapters. These chapters are divided as follow:
General rules: Introduction and Chapters 1 through 4 apply in general to all installations, this represents the scope of this book.

Special rules: Chapters 5 through 7 apply to special occupancies, equipment, or conditions and may modify the general rules of Chapters 1 through 4. Examples include; aircraft hangers, health care facilities, x-ray equipment, etc.

Communications Systems: Chapter 8 covers communications systems (phone, CATV, satellite dishes, etc.). This chapter of the NEC is independent of the other chapters. This means that the rules of Chapters 1 through 4 do not apply to Chapter 8, unless there is a specific reference in Chapter 8 to a rule in Chapters 1 through 4.

Tables: Chapter 9 consists of tables that are used for raceway sizing and conductor fill and voltage drop.

90-4 Enforcement

The NEC, while purely advisory, is intended to be a document that can be adopted by governmental bodies and other inspection departments. It is up to these bodies, states, counties, cities, etc., to adopt the NEC as a legal requirement for electrical installations.

The enforcement of complying with the NEC falls under the authority having jurisdiction. For the purposes of this book, the authority having jurisdiction (AHJ) will be considered the electrical inspector. Generally, the electrical inspector is employed by some government agency and is responsible to an advisory council or board for his or her decisions or rulings.

An inspector's authority and responsibilities include:

Interpretation of the NEC Rules. This means that the inspector must have a specific rule upon which to base his/her interpretations. If an inspector rejects your installation, you have the right to know the specific NEC rule that you violated, but naturally, we must be realistic in the recognition that we must often submit to a higher authority, Fig. 1-4.

Note. The art of getting along with the electrical inspector, is knowing what the Code says and when to choose your battles.

Approval of Equipment and Materials. The electrical inspector is the person who decides the approval of equipment. However, if equipment is listed by a qualified electrical testing laboratory (listing agency), its internal wiring does not need to be reinspected at the time of installation [90-7].

Only the inspector can approve equipment [90-4]. He or she can reject the use of any equipment and can approve nonlisted equipment. The primary basis of equipment approval by the inspector is listing and labeling by qualified testing laboratories [90-7 and 110-2].

Waiver of Rules. Waiver of specific requirements of the Code or permitting alternate methods. When an installation does not comply with normal NEC rules, the inspector may waive specific requirements of the Code or permit alternate methods. This is permitted only where it is ensured that equivalent electrical safety can be achieved.

Waiver of new Code requirements on materials. Waiver of new Code requirements. If the 1999 Code requires materials, products, or construction that are not yet available, the inspector may allow materials, products, and construction methods that were acceptable in the 1996 Code.

Note. It takes time for manufacturers to redesign, manufacture, and distribute new products to meet new Code requirements.

Ensure that equipment is installed properly [90-7]. It is the inspector's responsibility to ensure that the equipment is installed according to the equipment's listed or labeled instructions [110-3(b)].

Equipment Installation. It is the inspector's responsibility to ensure that the electrical equipment is installed to the equipment listing or labeling instructions. The inspector is also responsible for detecting any field modification of equipment. Listed equipment may not be modified in the field without the approval of the listing agency or the electrical inspector [90-7, 110-3(b)].

90-5 Mandatory Rules and Explanatory Material

(a) Mandatory Rules. Rules that identify actions that are specifically required or prohibited are characterized by the use of the terms "shall" or "shall not."

Section 110-3(b) states that listed or labeled equipment "shall" be installed, used, or both, in accordance with any instructions included in the listing or labeling.

(b) Permissive Rules. Rules which identify actions that are allowed but not required, such as options or alternative methods are characterized by the use of the terms "shall be permitted" or "shall not be required." A "permissive rule" is often an exception to the general requirement.

Section 250-102(d) states that the equipment bonding jumper can be installed inside or outside of a raceway or enclosure.

(c) Explanatory Material. Explanatory material, such as references to other standards, references to related Sections of the Code, or information related to a Code rule is included in the form of a Fine Print Note (FPN). Fine Print Notes are informational only and are not to be enforced. Most FPN's contain a reference to another related Code Section.

90-6 Formal Interpretations

National Fire Protection Association (NFPA) formal interpretation procedures are listed in the Regulations Governing Committee Projects, available from the NFPA Secretary of the Standards Council. This is a very time-consuming process and is rarely done. Not only that, but formal interpretations are not legally binding.

90-7 Product Safety

Product safety evaluation is done by nationally recognized independent testing laboratories that publish lists of equipment that meet nationally recognized test standards. Products and materials that are listed, labeled, or identified by a responsible and respected organization, are the basis of approval by the electrical inspector. National testing laboratories decrease the need for inspectors to reinspect or evaluate the electrical equipment at the time of installation.


The purpose of the NEC is for the protection of persons and property.
The NEC is a safety standard.
The NEC is not intended as a design specification or an instruction manual for untrained persons.
The NEC covers most electrical installations, but not all.
The NEC does not cover cars, trucks, boats, ships, planes, underground mines, trains, utility controlled communication equipment, and utility power distribution locations.
The NEC covers commercial parking lot lighting installed by the electric utility on private property.
The NEC is divided into an Introduction and nine Chapters.
Product evaluation is done by nationally recognized independent testing laboratories, not the electrical inspector.
The authority having jurisdiction (AHJ) approves the use of products and enforces the requirements of the NEC, but they cannot make-up their own rules.
Mandatory Code rules use the word shall.
Permissive Rules identify actions that are allowed but not required, such as options or alternative methods.
Explanatory material is contained in the Fine Print Notes (FPNs).
Product safety evaluation is done by nationally recognized independent testing laboratories.

If you would like the information (with graphics), please consider ordering my best selling book "Understanding the 1999 National Electrical Code". Call my office toll free 1-888-NEC CODE or Click here for more details.

God Bless, Mike

Special thanks to Mike Holt, renowned author and educator, for allowing us to share this information with you. You can learn more on this and other subjects through his excellent educational materials and seminars.




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