National Electrical Code 2005: Understanding Terms

By Consulting Specifying Engineer Staff October 31, 2004

By Ken Seaton, P.E.PrincipalSeaton & Associates


Editor’s Note: This is the second installment in a regular monthly column that will cover significant new issues raised by the 2005 Edition of the National Electrical Code.

Most electrical engineers are familiar with the many technical words and phrases used in the NEC. Understanding the meanings of words such as ground, grounded, grounding and neutral is essential. But if you do not clearly understand the terms used in a code book, you will have difficulty understanding the rules themselves. The 2005 NEC has some new and changed definitions that you should become familiar with.

Some may be obvious. But keep in mind that it isn’t always the technical words that require close attention. Even the simplest words can make a big difference in how one interprets the code. For example, the word “or” can mean an alternate choice for equipment, wiring methods or other requirements. But sometimes, the word “or” will mean any item in a group.

Likewise, the word “and” means an additional requirement or any item in a group. In addition, electricians, engineers and other professionals have their own slang. One of the problems with slang is that it means different things to different people. Consequently, these words are not used in the NEC.

In the 2005 NEC, a few definitions have been added. Three of the more significant ones are: system bonding jumper, grounding electrode and coordination (selective). The definition of device was revised to clarify requirements where the word is used.

The following are key definitions that have been added or amended in 2005 NEC:

Authority Having Jurisdiction (AHJ). The organization, office or individual responsible for approving equipment, materials, an installation or a procedure.

Bonding Jumper, System. The (physical) connection between the grounded circuit conductor and the equipment grounding conductor at a separately derived system.

Coordination (Selective). Localization of an overcurrent condition to restrict outages to the current or equipment affected, accomplished by the choice of overcurrent protective devices and their ratings or settings.

Device. A unit of an electrical system that is intended to carry or control, but not utilize, electric energy.

Dwelling Unit. A single unit, providing complete and independent living facilities for one or more persons, including permanent provisions for living, sleeping, cooking and sanitation.

Energized. Electrically connected to (a supply system), or is, a source of voltage (and current).

Grounded, Solidly. Connected to ground without inserting any resistor or impedance device.

Grounding Electrode. A device that establishes a (low impedance) electrical connection to earth.

Grounding Electrode Conductor. The conductor used to connect the grounding electrode(s) to the equipment grounding conductor, or to both, at the service, at each building or structure where supplied by a feeder(s) or branch.

Guest Room. An accommodation combining living, sleeping, sanitary and storage facilities within a compartment.

Handhole Enclosure. An enclosure identified for use in underground systems, provided with an open or closed bottom, and sized to allow personnel to reach into, but not enter, for the purpose of installing, operating or maintaining equipment or wiring or both.

Outline Lighting. An arrangement of incandescent lamps, electrical discharge lighting or other electrically powered light sources to outline or call attention to certain features, such as the shape of a building or the decoration of a window.

Separately Derived System. A premises wiring system whose power is derived from a source of electric supply or equipment other than a service. Such systems have no direct electrical connection, including a solidly connected grounded circuit conductor, to supply conductors originating in another system.

Supplementary Overcurrent Protective Device. A device intended to provide limited overcurrent protection for specific applications and utilization equipment, such as luminaries (lighting fixtures) and appliances. This limited protection is in addition to the protection provided in the required branch circuit overcurrent protective device.