Why Article 100 Matters
Article 100 is the cornerstone of the entire National Electrical Code. Every term defined here carries a specific technical meaning that may differ from its everyday usage. Misunderstanding a single definition can lead to incorrect code application, failed inspections, and unsafe installations. For exam purposes, a solid command of these definitions is essential because questions frequently test whether you can distinguish between closely related terms.
Exam Tip: Many NEC exam questions are designed to test your understanding of definitions rather than complex calculations. Never assume a term means what it does in common speech.
General Definitions
Article 100 contains definitions of terms that appear in two or more articles of the NEC. Terms used in only one article are defined within that specific article. Key general definitions include:
- Accessible (as applied to equipment): Admitting close approach; not guarded by locked doors, elevation, or other effective means.
- Accessible (as applied to wiring methods): Capable of being removed or exposed without damaging the building structure or finish.
- Dwelling Unit: A single unit providing complete and independent living facilities for one or more persons, including permanent provisions for living, sleeping, cooking, and sanitation.
- Premises Wiring: Interior and exterior wiring, including power, lighting, control, and signal circuit wiring, together with their associated hardware, fittings, and wiring devices.
Circuit Classifications
Understanding how the NEC classifies circuits is critical for applying the correct rules:
- Branch Circuit: The circuit conductors between the final overcurrent device protecting the circuit and the outlet(s). Branch circuits are further classified by their rating (15A, 20A, 30A, 40A, 50A) or as individual or multiwire.
- 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.
- Service: The conductors and equipment for delivering electric energy from the serving utility to the wiring system of the premises served.
Branch Circuit vs. Feeder
A common source of confusion is the distinction between branch circuits and feeders. The key differentiator is the final overcurrent protective device. Everything downstream of it is a branch circuit; everything upstream (back to the service or source) is a feeder.
Grounding and Bonding Terms
The NEC draws precise distinctions between grounding and bonding concepts:
- Grounded (Grounding): Connected (connecting) to ground or to a conductive body that extends the ground connection. This refers to the intentional connection to earth.
- Grounding Conductor, Equipment (EGC): The conductive path installed to connect normally non-current-carrying metal parts of equipment to the system grounded conductor, the grounding electrode conductor, or both.
- Bonding (Bonded): The permanent joining of metallic parts to form an electrically conductive path that ensures electrical continuity and the capacity to safely conduct any fault current likely to be imposed.
- Bonding Jumper: A reliable conductor to ensure the required electrical conductivity between metal parts required to be electrically connected.
Key Distinction: Grounding connects to the earth. Bonding connects metallic parts together. Both serve safety purposes, but they address different hazards.
Equipment Terminology
Several equipment-related definitions appear frequently on exams:
- Listed: Equipment, materials, or services included in a list published by a nationally recognized testing laboratory (such as UL).
- Labeled: Equipment or materials with a label, symbol, or other identifying mark from a nationally recognized testing laboratory.
- Approved: Acceptable to the authority having jurisdiction (AHJ).
- Identified (as applied to equipment): Recognizable as suitable for the specific purpose, function, use, or environment.
Installation-Related Definitions
- Concealed: Rendered inaccessible by the structure or finish of the building. Wires in concealed raceways are considered concealed even if they become accessible by withdrawing them.
- Exposed (as applied to wiring methods): On or attached to the surface, or behind panels designed to allow access.
- Wet Location: Installations underground or in concrete slabs in direct contact with the earth, and locations subject to saturation with water.
- Damp Location: Locations protected from weather and not subject to saturation with water but subject to moderate degrees of moisture.
Mastering these definitions provides the vocabulary needed to correctly interpret and apply every subsequent chapter of the NEC.
