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National Electrical Code Articles and Information

National Electrical Code Summary: Article 90 -- Introduction

Based on the 2020 NEC

by Mark Lamendola

NEC Article 90 draws boundaries around the National Electrical Code—boundaries many people fail to understand. For example, Article 90 has long made it clear the NEC is not intended as design specification or instruction manual. The National Electrical Code has one purpose only. Logically, Article 90 belongs in Chapter 1 (along with Article 80)

90.1 has four subdivisions:

90.2 describes the scope of the Code—what it covers and what it does not cover.

90.3 explains how the Code is arranged. Please note the influence of the international and engineering communities. For example, the Code uses the "dot" system of enumeration and the "Appendices" are called "Annexes."

90.4 gives the Authority Having Jurisdiction (AHJ) some flexibility in enforcement.

90.5 distinguishes between mandatory rules, permissive rules, and explanatory material. These often get confused. An example is a Fine Protection Note (FPN) that discusses voltage drop. The Code does not require addressing voltage drop—it merely explains that it is an additional consideration and gives a "rule of thumb." Unfortunately, many people have over-engineered to get "the Code-required drop" or have under-engineered because they were "within the Code requirements." The Code does not give voltage drop requirements.

90.6 discusses formal interpretations.

90.7 adds a dose of common sense regarding equipment inspections. For example, a product that is Listed (e.g., by U.L.) can be assumed to be adequate for the stated purpose and need not be inspected again (except for alterations or damage).

90.8 alerts the user to allow for expansion and to know that the Code does specify various restrictions on the number of wires and circuits in a given enclosure.

90.9 discusses units of measurement.

How the NEC is arranged

  1. The first four Chapters of the NEC apply to all installations.
  2. Article 90 precedes Chapter One, and establishes the authority of the NEC.
  3. Article 80 follows the body of the NEC; it exists as Annex H. It provides the requirements for administration.
  4. Chapters 5, 6, and 7 are the "special" chapters, covering special: occupancies, equipment, and conditions (in that order).
  5. Chapter 8 provides the requirements for communications systems.
  6. Chapter 9 provides tables.
  7. The appendices provide mostly reference information.
  8. Appendix D contains examples that every NEC user should study.

Try your NEC moxy:

  • Do you know the difference between bonding and grounding? Hint: Look in the NEC, Article 100.
  • Does the NEC refer to grounding incorrectly in any of its articles? Yes! So be careful to apply the Article 100 definitions. Don't ground where you should bond.
  • When doing motor load calculations, which Article covers hermetic motors? Answer: While Article 440 covers the application of hermetic motors, it does so only by amending Article 430 because hermetic motors are a special case of motors. For motor load calculations, refer to Article 430.
  • Does the NEC provide a voltage drop requirement? Yes! It does so in a special case, which is Article 648 Sensitive Electronic Equipment. But for general applications, it does not provide a requirement; it merely provides a recommendation in a couple of FPNs.
  • Take our Code Quizzes.

Remember other applicable codes, rules, standards, and references:

  • OSHA's electrical worker safety rules.
  • IEEE standards.
  • NETA standards.
  • NFPA standards.
  • International Codes (if applicable to the installation).
  • State Codes (if the state has them).
  • Local ordinances and permit requirements.
  • Local fire codes.
  • Manufacturer requirements or guidelines.
  • Customer security requirements.
  • Industry standards.
  • Your company's own internal standards, practices, and procedures.
  • Engineering drawing notes.


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