Understanding the NEC
Extracted from Mike Holt's best selling book Understanding the National Electrical Code.
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.
Table of Contents
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.
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 1996 NEC, be sure to submit it no later than November 1997. 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.
More than 3,500 proposed changes were submitted to the NFPA for the 1996 Code, of these only a few hundred were accepted. All proposals are reviewed by the National Electrical Code Committee, which consists of twenty Code-making panels. Each Code Panel has about fifteen to twenty members who represent special interest groups, such as inspectors, electrical workers, electrical contractors, testing laboratories, manufacturers, distributors, insurance organizations, and government regulatory authorities. See the front of the NEC for a complete list of committee members and who they represent.
Each Code Panel is assigned specific Code articles, for example; Panel No. 2 is responsible for Articles 210, 215, 220, and Chapter 9, Examples 1 through 6.
Before you can use the NEC, you must remember that is intended for use by experienced persons, such as electrical contractors, inspectors, electrical engineers, and qualified electricians. The NEC is not intended to be used as an instructive or teaching manual.
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.
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: 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.
In this book the first time a glossary term is used it will be printed in boldface type. Words that are defined in Article 100 of the NEC and which are particularly important to understand will be italicized in each unit. As you read each unit, please review both the glossary terms located in the back of this book and the important NEC definitions, located in Unit 2 - Article 100.
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.
This book does not cover all theoretical aspects of the NEC. As much as we would like to, I can't put everything into one book.
Contrary to popular belief, the NEC is a fairly well-organized document. The NEC does have some areas that are somewhat vague. Understanding the NEC structure and writing style is extremely important for understanding and using the Code Book. The National Electrical Code has nine components.
- Chapters (categories)
- Articles (subjects)
- Parts (subheadings)
- Sections and Tables (Code)
- Exceptions (Code)
- Fine Print Notes (explanatory material, not Code)
- Definitions (Code)
- Superscript Letter X
- 1996 Code Changes and Deletions
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 (the scope of this book)
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)
The NEC contains approximately 125 articles. An article is a specific subject, such as grounding, services, feeders, branch circuits, fixtures, motors, appliances, air conditioning, etc.
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 230 contains eight parts, such as Part A-General, Part B-Overhead Service Conductors, and Part H-Services Exceeding 600 Volts, Nominal.
4. Sections and Tables.
The actual NEC Code rule is called a section and is identified with numbers and letters. Many in the electrical industry use the slang term article when referring to a Code section. A Code section may be broken down into subsections (by letters in parentheses) and each subsection may be broken down further by numbers in parentheses. For example, the section that requires all receptacles in a dwelling unit bathroom to be GFCI protected is Section 210-8(a)(1).
Many Code sections contain tables, which are a systematic list of Code rules in an orderly arrangement. Example, Table 310-16 contains the ampacity of conductors.
Exceptions are in italic type and provide an alternate choice to a specific rule. There are two types of exceptions: One exception is mandatory and the other is permissible. When a rule has several exceptions, those exceptions with mandatory requirements are listed before those with permissible exceptions.
A mandatory exception uses the words shall or shall not in the wording. The word shall in an exception means that if you are using the exception, you shall do it in a particular way. The term shall not in an exception means that you shall not do something. A permissible exception uses such words as shall be permitted, this means that it's okay 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; therefore, there is no NEC requirement for conductor voltage drop.
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. Definitions at the beginning of a specific article apply to that article only. Definitions in a part of an article apply only to that part, and definitions in a specific Code section only apply to that section.
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 1993 NEC are identified in the margins of the 1996 NEC in the following manner: Changes are marked with a vertical line (|) and deletions of a Code rule are identified by a bullet (•).
What does Section 210-8(b)(1) mean? The first number indicates the chapter (Chapter 2). The numbers before the hyphen indicate the article (Article 210). The numbers after the hyphen indicate the Code section (Section 8), and the letter and numbers in parentheses after the section indicate the subsection. In this case, Section 210-8(b)(1) is the rule that requires all receptacles in commercial and industrial bathrooms to be GFCI protected.
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 B Over-600-volt Systems of Article 110! The working clearance rule for under-600-volt systems is located in Part A of Article 110, Table 110-16.
Everybody wants to be able to use the NEC quickly, but unfortunately it doesn't work that way. How you use the NEC depends on your experience. An experienced Code user rarely uses the index. He or she knows which Code articles contain which rules and uses the Table of Contents instead of the index.
Let me give you an example of how handy the Table of Contents can be. What Code rule indicates the maximum number of disconnects permitted for a service? Answer: You need to know that there is an Article for Services - 230, and this article has a Part for Disconnection Means. Use the Table of Contents to find that the answer is around page 90. I'm sorry that I can't tell you the exact page number, because this book was written about six months before the actual Code Book was printed.
Once you are familiar with the NEC (completed this book) you should use the index to find your way around the Code. The index lists subjects in alphabetical order, and is 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, or appendices by numbers.
Finding information in the NEC is very difficult if you don't understand the layout of its contents. In this exercise, we will explore some of the problems and challenges you will face while using the Code Book. Please use your Code Book for this exercise.
Find the ampacity of a No. 10 THHN. The key word is ampacity. Look up ampacities in the NEC index and you should see different subheadings under the boldface word ampacity. The first sub heading is Conductors 310-15, Tables 310-16 through 310-19, B-310-1 through B-310-10, 310-61 through 310-84, and 374-6.
The first (310-15) and last (374-6) listings are section numbers. The B-310-1 through B-310-10 are tables, but the B indicates that they are found in Appendix B at the back of the NEC. If you turn to the beginning of Appendix B in the back of your Code Book, the very first line tells you that the appendix is not part of the Code and that it is included only for informational purposes.
Back to the index. If we turn to Section 310-15 of the NEC, it tells us that the ampacity can be determined by one of two methods. In almost all cases we will use the method listed in subsection (a), which refers to Table 310-16. Find Table 310-16 in your Code Book, the first column (down) is the conductor size in American Wire Gauge or kcmil. Go down until you find the number 10. Now move across to the right to the THHN column (third column), you will find that No. 10 THHN has an ampacity of 40 amperes.
This ampacity is used only when there are no more than three conductors in the raceway or earth, based on an ambient temperature of 86°F (conditions listed at the top of Table 310-16). What is the No. 10 THHN ampacity if there are 6 conductors in the raceway? What if the ambient temperature is 106°F? What is ambient temperature anyway? It seems we're getting more questions than answers!
What is the maximum size circuit breaker (overcurrent protection device) that can be used to protect a No. 10 THHN conductor?
The Index has no reference to size, and the subheading for circuit breakers refers you to sections that will not give you the answer. Try looking up the word conductors, nothing there about breakers. Looks as if we are at a dead end. The problem is not the NEC or it's index; it's our lack of knowledge of the NEC terms. If you don't know that a circuit breaker is an overcurrent protection device (Article 240) you will go in circles trying to use the index. The key words are conductor overcurrent protection. Go to the subheading overcurrent protection under conductors. The 240-3 and 240-4 listings mean Sections 240-3 and 240-4.
Go to Section 240-3 in the NEC, now we seem to be getting somewhere. Section 240-3 contains the requirement of conductor overcurrent protection. But, all this section says is that conductors must be protected at their ampacity as specified in Section 310-15. If you go to Section 310-15, you will find a FPN (Fine Print Note) that refers you to Table 310-16.
The ampacity of No. 10 THHN is 40 amperes. Can we really put a 40- breaker on No. 10 THHN rated 40 amperes? No, the 40 amperes listed in the table has an obelisk symbol next to 40. The obelisk refers to the note at the bottom of Table 310-16, which indicates that the maximum overcurrent protection for No. 10 conductors is 30 amperes. The No. 10 THHN conductor has an ampacity of 40 amperes, but the maximum overcurrent protection device (circuit breaker) permitted on the conductor is 30 amperes.
You are wiring a motor control circuit with No. 18 fixture wire (TF, TFF, TFFN). How do you know the ampacity of No. 18 TF? Why isn't the ampacity of No. 18 TF, TFF or TFFN listed in Table 310-16? Again, it seems that we're getting more questions than answers.
If you don't know that TF stands for fixture wire, you would not be able to find the answer. Now, go back to ampacities in the index. There is a subheading fixture wires, and it lists Table 402-3. If you look at Section 402-3, you will find all kinds of information; but, it doesn't mention anything about ampacity. So, where is the ampacity? Look at Section 402-5, which is immediately after Table 402-3. Why didn't the index simply say Table 402-5 instead of Table 402-3? I don't know. There are some things about the NEC that you just have to know, and the only way to learn is through practice and experience.
Many people say the Code takes you in circles; it sometimes does, but most often, you take yourself in circles. The problem generally isn't the Code, but your inexperience in using and understanding the NEC. Becoming proficient with the NEC is a matter of practice.
This book should help you understand the NEC terms, the structure of the NEC, how to use the NEC, and what the NEC means. This can get you off to a great start, but you need to practice what you are learning to become truly proficient.
A certain attitude is required to understand the NEC. There are many different types of electrical installations, but the Code could not begin to consider all of them. If you are in the electrical industry, it is essential for your success that you 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 is still to learn.
There are some Code rules that the industry calls gray areas. As this book progresses, you will develop some insight into these rules. Yes, there are gray areas; but, generally the Code is quite clear.
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.
As you read this book, highlight those areas in your Code Book that are important to you. If there is any area of this book you don't understand, don't worry about it now. Simply highlight this book and later you can review these highlighted areas. It will be easier to understand those difficult areas when you have completed this book.
CAUTION: Before you get into the Code Book, review the following suggestions. Many of the Code articles are broken down into parts; the information following a part heading applies to that part only. ALWAYS remember which part you are in. You wouldn't want to be reading a rule in the over-600 volt-systems for an installation under 600 volts!
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.
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
(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. (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, installations complying with the NEC does not mean that the electrical system will be efficient, convenient, adequate for good service, or that it will work.
(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 adopted by local ordinance. (c) Design or Instruction Manual. The Code is not a how-to book, it is not intended as a design specification or an instruction manual for untrained persons.
The purpose of the NEC is for the protection of persons and property. The NEC is for safety. 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 does cover 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 approves the use of products and enforces the requirements of the NEC, but they can't make up their own rules. Mandatory rules use the word shall. Explanatory material is contained in the Fine Print Notes (FPN).
If you would like the information (with graphics) past Article 90, please consider ordering my best selling book "Understanding the 1996 National Electrical Code". Call my office toll free 1-888-NEC-CODE (632-2633) for more information.
God Bless, Mike