The National Electrical Code is written for people who understand electrical terms, theory, and trade practices. Such persons include electrical contractors, electrical inspectors, electrical engineers, and qualified electricians. The Code was not written to serve as an instructive or teaching manual for untrained persons [90-1(c)]. Learning to use the NEC is like learning to play the game of chess. You first must learn the terms used to identify the game pieces, the concepts of how each piece moves and the layout of how the pieces are placed on the board. Once you have this basic understanding of the game, you're ready to start playing it. But all you can do is make crude moves because you really don't understand what you're doing. To play the game well, you'll need to study the rules, understand the subtle and complicated strategies, and then practice, practice, practice. The same principle applies with the Code. Learning the terms, concepts, and layout of the NEC gives you just enough knowledge to be dangerous. Perhaps most difficult is learning the subtle meanings within the Code rules themselves. Thousands of different applications of electrical installations exist, but not every application has a specific Code rule. To properly apply the NEC, you must understand the safety-related issue of the rule and then apply common sense. NEC terms and concepts The Code uses many technical terms and expressions. It's crucial that all Code users understand the meanings of basic technical and Code terms such as ampere, backfed, induction, raceway, etc. to understand how to apply the rule itself. It is not only the technical words that require close attention in the NEC; even the simplest words can make a big difference. The word "or" can imply alternate choices for equipment, wiring methods, and other requirements. Sometimes "or" can mean any item in a group. The word "and" can be an additional requirement, or any item in a group. Finally, it's critical that the Code user have a good foundation of basic electrical circuitry, math and the formulas needed to apply many of the rules. Note. Electricians, engineers, and other trade-related professionals have created their own terms and phrases (slang or jargon). One of the problems with the use of slang terms is that the words mean different things to different people, resulting in confusion. Understanding the safety related concepts behind NEC rules means understanding how and why things work the way they do (electrical theory). How does a bird sit on an energized power line without getting toasted? Why, when we install a lot of wires close together, are we required to reduce the amount of current that each conductor can carry? Why can't a single current-carrying conductor be installed within a metal raceway? Why does the NEC permit a 40A circuit breaker to protect motor circuit conductors that are only rated 20A? Why are bonding jumpers sometimes required for metal raceways containing 480Y/277V circuits, but not for 120/240V circuits? If you understand why or how things work, you have a better chance of understanding the NEC rules. The NEC Style Understanding the NEC structure and writing style is extremely important to understand and use the Code 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 10. Table of Contents 11. Index 12. Appendices 1. Chapters. Each of the nine chapters contains articles. The nine chapters fall into four groupings: General Rules: Chapters 1 through 4 Specific Rules (Hazardous locations, signs, control wiring): Chapters 5 through 7 Communication Systems (Telephone, Radio/Television, and Cable TV Systems): Chapter 8 Tables: Chapter 9 2. Articles. The NEC contains about 125 articles. An article covers a specific subject as in the following examples: Article 110-General Requirements Article 250-Grounding Article 300-Wiring Methods Article 430-Motors Article 500-Hazardous (classified) Locations Article 680-Swimming Pools Article 725-Control Wiring Article 800-Communication Wiring 3. Parts. When an Article is sufficiently large, the Article is subdivided into Parts. For example, Article 250 contains nine parts, including: Part A. General Part B. Circuit and System Grounding Part C. Grounding Electrode System 4. Sections, Lists, and Tables. Sections. 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. Many in the electrical industry incorrectly use the term "article" when referring to a Code section. Lists. 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. 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. The two types of exceptions are mandatory and permissive. When a rule has several exceptions, those exceptions with mandatory requirements are listed before those written in permissive language. 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. 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 Note, (FPN), [90-5]. A Fine Print Note contains explanatory material intended to clarify a rule or give assistance, but it is not Code requirement. FPN's often use the term "may," but never "shall." 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. Article-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. Part-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. Section-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. The superscript letter X indicates that the material was extracted from other technical standards published by the NFPA. Appendix A, at the back of the Code, identifies the NFPA documents and the section(s) from which the material was extracted. 9. Changes and deletions. Changes and deletions to the NEC are identified in the margins of the 1999 NEC in the following manner: A vertical line (|) marks changes and a bullet identifies deletion of a Code rule. Many rules in the 1999 NEC were relocated. The place from which the Code rule was removed has a bullet in the margin, and the place where the rule was inserted has a vertical line (|) in the margin. 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. The four appendices in the 1999 NEC are:
Appendix A-Extract Information Appendix B-Ampacity Engineering Supervision
Appendix C-Conduit and Tubing Fill Tables Appendix D-Electrical Calculation Examples How to find things in the Code 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. Customizing your code book One way for you to get comfortable with your Code book is to customize it to meet your needs. You can do this 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-in. ruler to keep lines straight and neat. Because of the new format of the 1999 NEC (81/2 in. x 11 in.), 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, and 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 Sections or Articles that are important to you.