Reviewing the most current definitions in the NEC
Misunderstandings often occur in the field when people have different ideas of what words mean in the Code. The NEC contains Art. 100 (see SIDEBAR: What’s in 100? below) for this very reason. There, you’ll find definitions of key terms that appear in more than one Article. As a point of clarification, key terms appearing in only one Article are defined at the start of that Article.
The maximum current, in amperes, a conductor can carry continuously, where the temperature of the conductor won’t be raised in excess of its insulation temperature rating.
Analysis: The ampacity of a conductor is the maximum current it can carry (under the conditions of use), continuously, without exceeding its temperature rating. Previous editions of the Code didn’t include the word “maximum” in the definition, although a maximum seemed fairly obvious. This change corrects that omission.
An area that includes a basin and one or more of the following: toilet, urinal, tub, shower, bidet, or similar plumbing fixture.
Analysis: All 15A and 20A, 125V receptacles in bathrooms must be GFCI-protected [210.8(A)(1)]. As
non-traditional plumbing fixtures (e.g., bidets) and small rooms for their use are becoming more common, this definition needed updating. If a room contains only a basin and bidet, people call it a bathroom.
Bonding conductor or jumper
A conductor that ensures electrical conductivity between metal parts of the electrical installation.
Analysis: The 2008 NEC (and previous editions) referred only to “bonding jumpers.” This implies a short conductor, but length isn’t actually part of the meaning. For example, bonding conductors that connect grounding electrodes can be several feet long, and bonding jumpers for communications systems electrodes may exceed 20 ft.
Bonding jumper, system
The connection between the neutral conductor and the supply-side bonding jumper (SSBJ) or equipment grounding conductor (or both) at a separately derived system (Fig. 1).
Fig. 1. Article 100 clearly defines the meaning of a system bonding jumper.
An unintentional electrical connection between an ungrounded conductor and the metal parts of enclosures, raceways, or equipment.
Analysis: The NEC moved this definition from 250.2 to Art. 100 because the term is used in multiple Articles of the Code.
This term is no longer in the NEC.
Analysis: Recent revisions to Art. 100 and Art. 250 have made this term obsolete. The definition of “grounding conductor” has become nearly identical to the definition of “grounding electrode conductor,” resulting in confusion. The two terms have been (incorrectly) used interchangeably in past NEC editions. For example, in the 2008 Code, 250.64 refers to the installation of “grounding electrode conductors,” yet 250.64(A) refers to “grounding conductors,” not “grounding electrode conductors.” The use of more accurate and more specific terms, such as “grounding electrode conductor,” “bonding jumper,” or “bonding conductor,” in place of “grounding conductor” helps clarify the intention of the NEC.
The highest short circuit current at rated voltage the device is identified to interrupt under standard test conditions.
Analysis: The previous definition of interrupting rating referred to a device that’s “intended” to interrupt current. This change uses a defined term (“identified”) instead of an undefined one (“intended”).
Intersystem bonding termination
A device that provides a means to connect bonding conductors for communications systems to the grounding electrode system, in accordance with 250.94 (Fig. 2).
Fig. 2. This revision removes the requirements from the definition, leaving them in Art. 250 where they belong.
Analysis: The previous definition said where to locate this device (at the service equipment). This was a requirement inside of definition, and that’s never a good idea. In addition, this structure isn’t allowed by the NFPA NEC Style Manual. This revision removes the requirements from the definition, leaving them in Art. 250 where they belong.
Separately derived system
A wiring system whose power is derived from a source of electric energy or equipment other than the electric utility service. This includes a generator, battery, solar photovoltaic system, transformer, or converter winding, where there’s no direct electrical connection from circuit conductors of one system to circuit conductors of another system, other than connections through the earth, metal raceways, or equipment grounding conductors.
Analysis: The NEC previously said a separately derived system must not have any connections between itself and another system (such as the utility supply). While this makes good sense, it isn’t possible in all applications. Connections between systems occur through metallic enclosures, raceways, and similar equipment as well as through earth via grounding electrodes. This change clarifies that such incidental interconnections are permitted.
Service conductors, overhead
Overhead conductors between the service point and the first point of connection to the service-entrance conductors at the building/structure (Fig. 3).
Fig. 3. The NEC now clearly defines both overhead and underground service conductors.
Analysis: This is the first of many changes to terms related to the service and service conductors. These changes are part of a collective effort to help Code users understand the subtle differences between the many different types of service conductors.
Service conductors, underground
Underground conductors between the service point and the first point of connection to the service-entrance conductors in a terminal box, meter, or other enclosure, inside or outside the building wall (Fig. 4).
Fig. 4. The NEC defines underground service conductors as those between the service point and the first point of connection to the service-entrance conductors in a terminal box, meter, or other enclosure, inside or outside the building wall.
Analysis: This new term distinguishes between service lateral conductors and other service conductors installed underground. Underground service conductors are on the customer side of the service point, whereas service laterals (also installed underground) are on the electric utility side of the service point.
Overhead conductors between the utility electric supply and the service point.
Analysis: This term has been revised to clarify that only overhead conductors on the utility side of the service point are considered a service drop. Conductors installed overhead on the customer side are now “overhead service conductors.”
The definition of “service conductors” states that only conductors on the customer side of the service point are service conductors, so “service conductor” isn’t used here. A service drop does not contain service conductors.
Service-entrance conductors, overhead system
The conductors between the terminals of service equipment and service drop or overhead service conductors.
Analysis: The change clarifies that overhead service-entrance conductors begin at the end of the service drop or at the end of customer-owned overhead service conductors. These conductors end at the service equipment. Because they’re on the customer side of the service point, they’re service conductors.
Service-entrance conductors, underground system
The conductors between the terminals of service equipment and service lateral or underground service conductors.
Analysis: This change clarifies that underground service entrance conductors begin at the end of the utility’s service lateral or at the end of customer-owned underground service conductors. These conductors end at the service equipment. Because they’re on the customer side of the service point, they’re service conductors.
Underground conductors between the utility electric supply and the service point.
Analysis: This change clarifies that only underground conductors on the utility side of the service point are a “service lateral.” Conductors installed underground on the customer side are now “underground service conductors.”
[Art. 230]. The point where the electrical utility conductors make contact with premises wiring.
Analysis: The term “service point” is an important definition. It’s also such a simple one that it isn’t always fully understood. It’s the point where the serving utility ends and the premises wiring begins. The service point can be at the utility transformer, at the service weatherhead, or at the meter socket enclosure. Exactly where depends on where the utility conductors terminate.
As you go about your electrical work, you’re likely to be speaking with someone who’s using the old definitions — and thinking one thing while saying another. That’s never a good situation. To correct it, review the current Art. 100 definitions during each discussion in which key terms crop up. Don’t assume you understand or are understood — make sure.
SIDEBAR: What’s in 100?
Article 100 has two parts:
- Part I: Defines terms used throughout the Code for systems operating up through
- Part II: Defines terms that apply to systems operating at more than 600V, nominal.
SIDEBAR: Why a System Bonding Jumper?
The system bonding jumper provides a low-impedance fault current path to the power supply to facilitate the clearing of a ground fault (by opening the circuit overcurrent device). For more information, see 250.4(A)(5), 250.28, and 250.30(A)(1).