2.4 NEC Article 100 Essential Definitions for Journeymen
Key Takeaways
- Article 100 contains definitions essential to the proper application of the National Electrical Code. Terms defined apply throughout the entire code unless an article-specific definition modifies the scope.
- Accessibility distinguishes three strict legal tiers: 'Accessible (as applied to wiring methods)' (removable without damaging building finishes), 'Accessible (as applied to equipment)' (not guarded by locked doors or elevation), and 'Readily Accessible' (reached quickly without climbing, obstacles, portable ladders, or tools).
- A 'Continuous Load' is defined as maximum current expected to continue for 3 hours or more, mandating a 125% multiplier for conductor ampacity and overcurrent device ratings under NEC 210.19(A) and 215.2(A).
- A 'Device' is a unit of an electrical system intended to carry or control electric energy (switches, receptacles, circuit breakers), whereas 'Utilization Equipment' actually transforms electrical energy into light, heat, or mechanical power (motors, luminaires, heaters).
- 'Bonded (Bonding)' establishes electrical conductivity and continuity between metal parts to create an effective ground-fault current path, whereas 'Grounded (Grounding)' establishes an intentional connection to the earth.
Last updated: August 2026
2.4 NEC Article 100 Essential Definitions for Journeymen
In the National Electrical Code (NEC), precision of language is paramount. On the Idaho Journeyman Electrician exam, numerous questions test exact definitions located in NEC Article 100. Misinterpreting a single legal term—such as confusing accessible with readily accessible, or overload with overcurrent—leads directly to incorrect code navigation and calculation errors.
1. The Accessibility Triad
The Code strictly differentiates three levels of access to wiring methods and electrical equipment:
+-----------------------------------------------------------------------------+
| THE ACCESSIBILITY TRIAD |
| |
| TERM DEFINITION / CRITERIA REAL-WORLD EXAMPLE |
| ----------------------------------------------------------------------- |
| Accessible Capable of being removed or Junction box located |
| (Wiring Methods) exposed without damaging the above a drop ceiling |
| building structure or finish. with lay-in tiles. |
| |
| Accessible Admitting close approach; not Panelboard behind an |
| (Equipment) guarded by locked doors, unlocked door or in a |
| elevation, or other barriers. mechanical room. |
| |
| Readily Accessible Capable of being reached Main service breaker, |
| (Fast Access) QUICKLY without: receptacle, or GFCI |
| 1. Climbing over obstacles reset switch within |
| 2. Resorting to ladders normal reach (≤6'7"). |
| 3. Using portable tools |
+-----------------------------------------------------------------------------+
[!IMPORTANT] Exam Trap: Tools & Drop Ceilings: A junction box installed above a drywall ceiling with no access panel is NOT accessible. A junction box above a lay-in acoustic tile ceiling is accessible as applied to wiring methods, but it is NOT readily accessible because reaching it requires standing on a portable ladder or stool.
2. Grounding, Bonding & Conductor Classifications
Article 100 defines the precise roles of conductors in grounding and fault-clearing paths:
+-----------------------------------------------------------------------------+
| GROUNDING & BONDING DEFINITIONS IN ACTION |
| |
| +---------------------------------------------------------------------+ |
| | SERVICE PANEL | |
| | [Neutral Bus] <==== MAIN BONDING JUMPER ====> [Ground Bus / Encl] | |
| | | | | |
| +---------|----------------------------------------------|------------+ |
| | (Grounded Neutral) | (EGC) |
| v v |
| [White Conductor: Normal Current] [Bare/Green: Fault Current] |
| | | |
| v v |
| [UTILIZATION LOAD] ==========================> [METAL MOTOR FRAME] |
| (Bonded Enclosure) |
+-----------------------------------------------------------------------------+
Key Definitions:
- Bonded (Bonding): Connected to establish electrical continuity and conductivity between metal parts to ensure an effective ground-fault current path.
- Grounded (Grounding): Connected (intentionally or accidentally) to the earth or to some conducting body that extends the connection to the earth.
- Grounded Conductor: A system or circuit conductor that is intentionally grounded (typically the white or gray neutral conductor). It carries normal return current.
- Equipment Grounding Conductor (EGC): The conductive path(s) installed to connect normally non-current-carrying metal parts of equipment, raceways, and enclosures together and to the system grounded conductor or grounding electrode conductor. Does NOT carry current under normal operating conditions.
- Grounding Electrode Conductor (GEC): A conductor used to connect the system grounded conductor or equipment to a grounding electrode (such as a ground rod, metal water pipe, or concrete-encased electrode/Ufer).
- Main Bonding Jumper (MBJ): The connection between the grounded circuit conductor (neutral) and the equipment grounding conductor at the service disconnect.
- Neutral Conductor: The conductor connected to the neutral point of a system that is intended to carry current under normal conditions.
3. Circuit Topography: Branch Circuits vs. Feeders vs. Services
+-----------------------------------------------------------------------------+
| CIRCUIT TOPOGRAPHY SPECTRUM |
| |
| [UTILITY POLE / TRANSFORMER] |
| | |
| v (Service Drop / Lateral) |
| [SERVICE POINT] (Boundary of utility ownership & premises wiring) |
| | |
| v (Service-Entrance Conductors) |
| [MAIN SERVICE DISCONNECT / OCPD] |
| | |
| v (FEEDER: Between Service Disconnect and Subpanel OCPD) |
| [DISTRIBUTION SUBPANEL / OCPD] |
| | |
| v (BRANCH CIRCUIT: Between Final OCPD and Outlets) |
| [OUTLETS: Receptacles, Switches, Luminaires, Hardwired Loads] |
+-----------------------------------------------------------------------------+
Definitional Rules:
- Service Point: The point of connection between the facilities of the serving utility and the premises wiring.
- Service Conductors: The conductors from the service point to the service disconnecting means.
- 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.
- Branch Circuit: The circuit conductors between the final overcurrent device protecting the circuit and the outlet(s).
4. Hardware Terms: Devices vs. Equipment vs. Utilization Equipment
| Term | Official Article 100 Definition | What It Includes | What It DOES NOT Include |
|---|---|---|---|
| Device | A unit of an electrical system, other than a conductor, that carries or controls electric energy as its principal function. | Switches, receptacles, circuit breakers, fuses, relays, contactors. | Motors, lights, heaters, appliances (these consume power). |
| Utilization Equipment | Equipment that utilizes electric energy for electronic, electromechanical, chemical, heating, lighting, or similar purposes. | Motors, luminaires, water heaters, ranges, transformers powering loads. | Wall switches, standard receptacles, disconnect switches. |
| Equipment | A general term including fittings, devices, appliances, luminaires, apparatus, machinery, and like parts used as a part of, or in connection with, an electrical installation. | Comprehensive umbrella term covering all electrical hardware. | Non-electrical framing or structural lumber. |
5. Overcurrent, Overload & Fault Classifications
+-----------------------------------------------------------------------------+
| OVERCURRENT CLASSIFICATION TAXONOMY |
| |
| OVERCURRENT |
| (Any current in excess of rated equipment ampacity) |
| | |
| +--------------------+--------------------+ |
| | | |
| v v |
| OVERLOAD FAULT CONDITIONS |
| • Excessive operating demand • Direct insulation failure |
| • Persists over time • Massive instantaneous current |
| • Examples: Motor mechanical jam, • Types: |
| too many heaters on one circuit 1. Short Circuit (Phase-Phase) |
| • No insulation breakdown 2. Ground Fault (Phase-Ground) |
+-----------------------------------------------------------------------------+
Critical Code Distinctions:
- 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 that, when it persists for a sufficient length of time, would cause damage or dangerous overheating. A fault, such as a short circuit or ground fault, is NOT an overload.
- Short Circuit: An abnormal connection of relatively low impedance, whether made intentionally or accidentally, between two points of different potential (e.g., hot-to-hot or hot-to-neutral).
- Ground Fault: An unintentional, electrically conductive connection between an ungrounded conductor of an electric circuit and the normally non-current-carrying conductors, metallic enclosures, metallic raceways, metallic equipment, or earth.
6. Other High-Yield Article 100 Definitions
Continuous Load
Definition: A load where the maximum current is expected to continue for 3 hours or more.
- Exam Application: Under NEC 210.19(A)(1) and 215.2(A)(1), branch circuit and feeder conductors/OCPDs must be sized for 125% of the continuous load plus 100% of noncontinuous loads.
In Sight From (Within Sight From / Within Sight)
Definition: Where specified that equipment shall be "in sight from," the specified equipment shall be visible and not more than 50 feet (15 m) distant from the other.
- Exam Application: Motor disconnects, HVAC disconnects, and water heater servicing disconnects must be visible and within 50 ft.
Separately Derived System (SDS)
Definition: An electrical source, other than a service, having no direct connection(s) to circuit conductors of any other electrical source other than those established by grounding and bonding connections.
- Common Examples: Distribution transformers (480V Delta to 208Y/120V Wye), standalone solar systems, or generators where the transfer switch switches the neutral conductor.
Ampacity
Definition: The maximum current, in amperes, that a conductor can carry continuously under the conditions of use without exceeding its temperature rating.
Test Your Knowledge
An electrical disconnect switch is installed inside a commercial mechanical room on a wall at a height of 5 feet above the finished floor. The room is accessible through an unlocked door, and there are no obstructions in front of the switch. How is this disconnect classified under NEC Article 100?
A
B
C
D
Test Your Knowledge
Which of the following is defined under NEC Article 100 as 'a unit of an electrical system, other than a conductor, that carries or controls electric energy as its principal function'?
A
B
C
D
Test Your Knowledge
According to NEC Article 100, what is the maximum distance allowable between two pieces of equipment for one to be considered 'in sight from' the other?
A
B
C
D