National Electrical Code Top Ten Tips: Article 100 -- Definitions

Based on the 2023 NEC.

My remarks in are parentheses. Please note, I 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. It will, however, help you better understand and use the NEC.

These are the 10 Article 100 definitions I deem most important, based on the pervasiveness of confusion and the potential costs of same. That is not to say other definitions are not also important. Also note that in your particular situation, there may be several definitions more important to you than these. Make a point of learning the NEC definitions, rather than assuming on the fly.

Definitions that appear in Article 100 apply to more than one Article in the NEC. A definition that is used only in one Article will appear in section 2 of that Article (e.g., 410.2). What if you come across a word you don't know, and it's not in subsection 2 or Article 100? Then look it up. If there's more than one definition for that word, consider the context in which it's being used.

A great way to get up to speed is to set aside "Definition Day" two or three times a week. Keep track of where you left off, each time. What you do is read the first three definitions, slowly. Read them a second time. The next Definition Day, you read those again and add one definition. The next Definition Day, you add one more. From this point forward, you drop the "oldest" definition as you add one more. You will have read all of these definitions several times. By sheer osmosis, most of them will stick. If you work with a particular Article that has its own definition(s) in section 2, then study those.

Now, for my list.

1. Ampacity. "The maximum 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.) Note that the word "maximum" was added with the 2003 NEC. From a composition standpoint, this is an unnecessary addition. The meaning is obvious without it.
    
2. Bonding. The 2017 definition is "Connected to establish electrical continuity and conductivity." The 2020 revision kept this definition. The 2023 revision also kept it. And that is a shame. I don't think this definition is, well, definitive. What do they mean by "electrical continuity" and how does that differ from conductivity? Can you have a chunk of 4 gage wire that is electrically continuous but not conductive? Or conductive but not electrically continuous? Puzzling....
   
   I like an earlier definition better, so here it is: "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." The reason for the newer definition is it's presumably simpler. People were questioning how they were supposed to know how much current was likely to be imposed. This new definition just gave them something different to question.
   
   Here is a definition that makes better sense, though it is not (yet) in the NEC. "A metallic path that is mechanically sound enough to reliably provide electrical continuity between metallic objects, with the purpose of eliminating dangerous differences of potential." If you use this definition in your work, while also using the Article 250 Part V details, you will correctly bond things.
   
   Bonding is not the same as grounding, but bonding jumpers are essential components of the bonding system, which eventually ties into 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.) Nice, simple definition.
    
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. The 2017 definition is "The earth." The 2020 revision kept this definition. So did the 2023 revision. I'm happy about that, for multiple reasons. Here's an earlier definition: "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." Can you guess one reason I'm happy this definition has survived three Code cycles now?
   
   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.
    
6. 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.)
    
7. Grounding conductor. This term disappeared with the 2017 NEC. Here's the (earlier) definition: "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.) This term came back with the 2023 revision (we missed you!), but now as two variations:
   1. Grounding conductor, equipment. Equipment Grounding Conductor or EGC. It's actually a bonding conductor, and 250.118 lists which kinds of wiring methods can be used for this purpose. Metallic objects are bonded to each other to eliminate dangerous differences of potential. At some point, this system of bonding conductors connects to the power source ground. I'll discuss its definition in #8 below.
   2. Grounding conductor, impedance. Impedance Grounding Conductor. A conductor that connects the system neutral point to the impedance device in an impedance grounded system.
   
8. Grounding equipment conductor. Yes, I am visiting this one again, since #7 consists of two variations. Here's the 2020 definition: "A conductive path(s) that is part of an effective ground-fault current path and connects normally on-current carrying metal parts of equipment together and to the system grounded conductor or to the grounding electrode conductor, or both." This is a slight update to the 2017 definition. I think it's more precise. The 2023 definition is the same.
   
   Here's an earlier definition: "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 one.)
    
9. 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.")
    
10. Listed. "Equipment, materials, or services included in a list published by an organization that is 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.)