National Electrical Code Summary: Article 90, Introduction.

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 electricity."
• (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 can do.
• (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 drop requirements.

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.

Learn more about Article 90 with the Mike Holt NEC General Requirements course: