2.3 Article 100 Definitions You Must Know Cold
Key Takeaways
- Article 100 definitions govern wherever the defined term appears in the Code, unless a specific article supplies its own modified definition for its scope.
- Accessible (equipment) means admitting close approach and not guarded by locked doors, elevation, or other effective means; Readily Accessible adds that reaching it must not require ladders, climbing over obstacles, or removing barriers.
- Ampacity is the maximum current a conductor can carry continuously under the conditions of use without exceeding its temperature rating.
- A Feeder runs between the service equipment or other supply source and the final branch-circuit overcurrent device; the Branch Circuit runs from that final overcurrent device to the outlets.
- The 2020 NEC added the defined terms Reconditioned and Retrofit Kit, and revised the definitions of Bonding Jumper, Supply-Side Bonding Jumper, and Overcurrent.
Why Definitions Decide Questions
NEC terms are legal terms. "Accessible" in the Code does not mean what it means in ordinary speech, and a question that turns on the difference between accessible and readily accessible has one right answer regardless of trade habit. Article 100 definitions apply wherever the term appears throughout the Code; where an individual article needs a narrower meaning for its own scope, it supplies its own definition in its .2 section.
Accessibility — Three Distinct Terms
| Term | Definition (paraphrased from Article 100) | Typical application |
|---|---|---|
| Accessible (as applied to wiring methods) | Capable of being removed or exposed without damaging the building structure or finish, or not permanently closed in by the structure or finish | Junction box above a lay-in ceiling; splices must remain accessible per 314.29 |
| Accessible (as applied to equipment) | Admitting close approach; not guarded by locked doors, elevation, or other effective means | Equipment reachable with a ladder |
| Readily Accessible | Capable of being reached quickly for operation, renewal, or inspection without requiring those to whom ready access is requisite to take actions such as to use tools (other than keys), to climb over or under, to remove obstacles, or to resort to portable ladders | Service disconnect (230.70), overcurrent devices (240.24) |
The 2020 definition of Readily Accessible contains a parenthetical that matters: tools other than keys. A locked door alone does not defeat ready accessibility where the lock is under the control of the people who need access — an informational note addresses locks under controlled or supervised industrial conditions. But an eight-foot mounting height requiring a portable ladder does defeat it.
Circuit Vocabulary
- Branch Circuit. The circuit conductors between the final overcurrent device protecting the circuit and the outlet(s).
- Appliance branch circuit — supplies outlets to which appliances are connected, with no permanently connected luminaires that are not part of an appliance.
- General-purpose branch circuit — supplies two or more receptacles or outlets for lighting and appliances.
- Individual branch circuit — supplies only one utilization equipment.
- Multiwire branch circuit — two or more ungrounded conductors with a voltage between them, and a grounded conductor with equal voltage between it and each ungrounded conductor, that is connected to the neutral or grounded conductor of the system.
- 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.
- Outlet. A point on the wiring system at which current is taken to supply utilization equipment. Note that an outlet is not the same thing as a receptacle — a hardwired luminaire is at an outlet.
- Receptacle. A contact device installed at the outlet for the connection of an attachment plug or for the direct connection of electrical utilization equipment designed to mate with the corresponding contact device. A single receptacle is a single contact device with no other contact device on the same yoke or strap; a multiple receptacle has two or more.
- Device. A unit of an electrical system, other than a conductor, that carries or controls electric energy as its principal function.
Ampacity and Related Terms
- Ampacity. The maximum current, in amperes, that a conductor can carry continuously under the conditions of use without exceeding its temperature rating.
- Continuous Load. A load where the maximum current is expected to continue for three hours or more. This drives the 125 percent rule in 210.19(A), 210.20(A), 215.2(A) and 215.3.
- Overcurrent. Any current in excess of the rated current of equipment or the ampacity of a conductor — it may result from overload, short circuit, or ground fault.
- Overload. Operation of equipment in excess of normal full-load rating, or of a conductor in excess of rated ampacity, which, when it persists for a sufficient time, would cause damage or dangerous overheating. A fault such as a short circuit or ground fault is not an overload.
Grounding and Bonding Vocabulary
These six terms are frequently swapped in distractor options:
| Term | Meaning |
|---|---|
| Grounded Conductor | A system or circuit conductor that is intentionally grounded — usually the neutral |
| Grounding Electrode | A conducting object through which a direct connection to earth is established |
| Grounding Electrode Conductor (GEC) | A conductor used to connect the system grounded conductor or the equipment to a grounding electrode or to a point on the grounding electrode system |
| Equipment Grounding Conductor (EGC) | The conductive path installed to connect normally non-current-carrying metal parts of equipment together and to the system grounded conductor or the GEC, or both |
| Bonding Jumper, Main (MBJ) | The connection between the grounded circuit conductor and the equipment grounding conductor at the service |
| Bonding Jumper, System (SBJ) | The connection between the grounded circuit conductor and the supply-side bonding jumper, the equipment grounding conductor, or both, at a separately derived system |
Two more from the same family: an Equipment Bonding Jumper is the connection between two or more portions of the equipment grounding conductor, and a Supply-Side Bonding Jumper is a conductor installed on the supply side of a service, or within a service equipment enclosure, or for a separately derived system, that ensures the required electrical conductivity between metal parts required to be electrically connected.
Service Vocabulary
- Service. The conductors and equipment connecting the serving utility to the wiring system of the premises served.
- Service Point. The point of connection between the facilities of the serving utility and the premises wiring. Everything on the utility side is outside the NEC per 90.2(B)(5).
- Service Conductors. The conductors from the service point to the service disconnecting means.
- Service Equipment. The necessary equipment, usually one or more circuit breakers or switches and fuses and their accessories, connected to the load end of service conductors and intended to constitute the main control and cutoff of the supply.
- Separately Derived System. An electrical source, other than a service, having no direct connection to circuit conductors of any other source other than through grounding and bonding connections. A transformer secondary and most generators qualify; a transfer switch that keeps the neutral solidly connected does not.
New and Revised in the 2020 Edition
- Reconditioned. Electromechanical systems, equipment, apparatus, or components that are restored to operating conditions — the 2020 Code added this term and used it in many articles to restrict reconditioning of specific equipment.
- Retrofit Kit. A general term for a complete subassembly of parts and devices for field conversion of utilization equipment.
- Overcurrent Protective Device, Branch-Circuit and Supplementary — the definitions were relocated to Article 100 in 2020.
Qualified Person
One who has skills and knowledge related to the construction and operation of the electrical equipment and installations and has received safety training to recognize and avoid the hazards involved. Both halves are required — experience alone does not make a person qualified under the Code definition.
A 200-ampere service disconnect is mounted so that the operating handle is 8 feet above the finished floor, requiring a portable ladder. How does Article 100 classify this equipment?
Which conductors are the feeder in a system running from the service equipment through a subpanel to a lighting outlet?
Under the Article 100 definition of Continuous Load, what duration of maximum current triggers the 125 percent sizing rules?
Which Article 100 term describes the connection between the grounded circuit conductor and the equipment grounding conductor at the service equipment?