National Electrical Code Articles and Information
National Electrical Code Summary: Article 90 -- Introduction
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.
NEC 90.1 has four subdivisions:
- (A) says the purpose of the NEC is the practical safeguarding of
people and property "from hazards arising from the use of
- (B) distinguishes from the adequacy concept (provisions necessary
for safety) and other concepts. The Code is a minimum standard.
Further effort may be required for an installation to be efficient,
convenient, or adequate for good service or future expansion. This
is a fundamental concept upon which many Code disagreements arise.
The Code is not a target you’d like to hit. It is the minimum you
- (C) clearly states the Code is not intended to be a design
specification or instruction manual.
- (D) ties the Code to international standards. The Code-making
panels do have members who are in countries other than the USA. The
intention is to draw on the collective wisdom of the international
community. Many people who make the Code what it is are also members
of the IEEE. Standards published by the IEEE frequently get review
from people who serve on NEC committees and vice-versa.
NEC 90.2 describes the scope of the Code—what it covers and what it
does not cover.
NEC 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."
NEC 90.4 gives the Authority Having Jurisdiction (AHJ) some
flexibility in enforcement.
NEC 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
NEC 90.6 discusses formal interpretations.
NEC 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).
NEC 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.
NEC 90.9 discusses units of measurement.
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Learn more about:
How the NEC is arranged
- The first four Chapters of the NEC apply to all installations.
- Article 90 precedes Chapter One, and establishes the authority of the NEC.
- Article 80 follows the body of the NEC; it exists as Annex H. It provides the requirements for administration.
- Chapters 5, 6, and 7 are the "special" chapters, covering special: occupancies, equipment, and conditions (in that order).
- Chapter 8 provides the requirements for communications systems.
- Chapter 9 provides tables.
- The appendices provide mostly reference information.
- 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.