Understanding the National Electrical Code®

A fundamental understanding of how the National Electrical Code® (NEC®) is structured and organized is important to passing any electrical exam.

The NEC® is organized by Chapters, Articles, Parts, Section and Subsections.

NEC structure

There are nine Chapters, Chapter 1 contains General information. Chapter 2 is specific to Wiring and Protection. Chapter 3 covers Wiring Methods and Materials. Chapter 4 includes Equipment for General Use. Chapter 5, 6, and 7 apply to Special Occupancies, Equipment and Conditions. Chapter 8 covers Communications Systems and Chapter 9 contains Tables.

NEC structure 2

Articles are chapter subdivisions that cover specific subjects such as Definitions, Branch Circuits, Health Care Facilities, etc. Articles, depending on the subject, are typically subdivided into Parts and designated by Roman numerals. Parts are usually overlooked, but they can be exceptionally useful when searching for a specific code reference. Sections contain the “rules”. Sections can be subdivided up to three levels, these levels of subdivision are called Subsections.

Exceptions provide alternate methods to the rule under specific conditions. Exceptions only apply to Sections or Subsections and they immediately follow the main rule to which they apply.

The Table of Contents is a very useful tool. It provides a road map of the National Electrical Code®. It is organized by Chapters, Articles and Parts.

Informative Annexes are not part of the enforceable requirements of the Code Book, they are included for informational purposes only. Some of the more useful Informative Annexes are Annex A which lists Product Safety Standards, Annex C contains Conduit and Tubing Fill Tables for Conductors and Fixture Wires of the Same Size, Annex D has examples of various calculations, and Annex I provides Recommended Tightening Torque Tables.

The Index is an alphabetical list of words and phrases with corresponding code references. The Index can be the most useful part of the codebook.

Article 90 is the Introduction to the National Electrical Code®. It contains the purpose, scope, and other administrative provisions. Section 90.3 and Fig. 90.3 provides how the NEC® is arranged. Chapters 1-4 apply generally to all electrical installations. Chapters 5-7 supplements or modifies Chapters 1-7. Chapter 8 is not subject to the requirements of Chapter 1-7 except where the requirements are specifically referenced in Chapter 8. Chapter 9, the Tables Chapter, is applicable as referenced. Section 90.5 tells us that Mandatory Rules are identified with the terms shall or shall not. Permissive Rules are allowed, but not required, and use the terms shall be permitted or shall not be required. Explanatory Materials are included in the form of Informational Notes. Informational Notes are not enforceable code requirements.

Changes are indicated with gray shading within sections. An entire figure caption with gray shading indicates a change to an existing figure. New sections, tables, and figures are indicated by a bold, italic N in a gray box to the left of the new material. An N next to an Article title indicates that the entire Article is new. Where one or more complete paragraphs have been deleted, the deletion is indicated by a bullet (•) between the paragraphs that remain.

Understanding the NEC® can only be achieved by using it. It’s going to take time and patience.PET Logo Book Only


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