Saturday, July 18, 2009

National Electrical Code Top Ten Tips: Article 100, Definitions

Our remarks in are parentheses. Please note, we do quote from copyrighted material. While the NFPA does allow such quotes, it does so only for the purposes of education regarding the National Electrical Code. This article is not a substitute for the NEC.

These are the 10 NEC definitions we deem most important, based on the pervasiveness of confusion and the potential costs of same.

  1. Ampacity. "The current, in amperes, that a conductor can carry continuously under the conditions of use without exceeding its temperature rating." (Ampacity varies depending on many factors. You must use the appropriate NEC Tables to determine the correct ampacity.)
  2. Bonding. "The permanent joining of metallic parts to form an electrically conductive path that ensures electrical continuity and the capacity to conduct safely any current likely to be imposed." (This is not the same as grounding, but bonding jumpers are essential components of the bonding system, which is an essential component of the grounding system. Please note that the NEC does not authorize the use of the earth as a bonding jumper—that’s because the resistance of the earth is more than 100,000 times greater than that of a bonding jumper.)
  3. Continuous Load. "A load where the maximum current is expected to continue for 3 hours or more." (That is the maximum running current, exclusive of starting current.)
  4. Feeder. "All circuit conductors between the service equipment, the source of a separately derived system, or other power supply source and the final branch-circuit overcurrent device." (If there is no branch circuit, a circuit originating at the service equipment is a feeder. This is a common approach for powering large motors.)
  5. Ground. "A conducting connection, whether intentional or accidental, between an electrical circuit or equipment and the earth or to some conducting body that serves in place of the earth." (Please note, simply driving an electrode into the earth does not constitute grounding a circuit. The ground must be made with respect to the supply—service entrance or separately derived system—because electrons are always trying to get back to the source. See
  6. for more information on this topic.)
  7. Grounded conductor. "A system or circuit conductor that is intentionally grounded." (This conductor isn’t meant to serve as the grounding path. It is simply a conductor that is grounded. The neutral is grounded on the service side of the service transformer.)
  8. Grounding conductor. "A conductor used to connect equipment or the grounded circuit of a wiring system to a grounding electrode or electrodes." (This is your supply "ground wire," not the neutral.)
  9. Grounding equipment conductor. "The conductor used to connect the non-current-carrying metal parts of equipment, raceways, and other enclosures to the system grounding conductor, the grounding electrode conductor, or both, at the service equipment or at the source of a separately derived system." (Note the difference between this and the preceding items.)
  10. Labeled. "Equipment or materials to which has been attached a label…acceptable to the authority having jurisdiction…." (It’s important to read the entire original definition, and distinguish this from "Listed."
  11. Listed. Equipment, materials, or services included in a list…acceptable to the acceptable to the authority having jurisdiction…." (Listing is usually done by an organization like U.L. Most authorities will not recognize an item as Listed unless it is also Labeled. Here, too, reading the entire definition is a useful exercise.)

Learn more about Article 100 with the

No comments:

Post a Comment