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.
- 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
- 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.)
- 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.)
- 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
- 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.
- 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
- 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.)
- 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.)
- 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."
- 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