Understanding the NEC


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 (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)

2. Articles.

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.

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 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.

5. Exceptions.

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.

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. 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 (Ã).

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