Definitions and general rules

Why it matters

The NEC is precise about words. "Grounded" and "grounding" mean different conductors; a "receptacle" is not the same as an "outlet"; and whether a load is "continuous" changes how big the wire and breaker must be. Exam questions often hinge on a single definition, and so do inspection calls. If you misread a defined term, you misapply the rule that uses it.

Awareness level only. Reading definitions is safe desk work, but applying them in the field requires employer or apprenticeship training and supervision by a licensed electrician.

Where definitions live

Article 100 holds the definitions used in two or more articles. Since the 2023 edition, Article 100 also collects most definitions that used to sit at the start of individual articles, so look there first. A few articles still carry their own terms. When a word is defined, the code means exactly that definition, not the everyday meaning.

Use Article 100 alphabetically, the way you would use a dictionary. When a section uses a word you are unsure about, stop and look it up before applying the rule.

Key definitions to know cold

These terms come up in almost every lesson of this course. The wording below is a plain-English paraphrase: read the exact definitions in the code book.

• Ampacity: the maximum current 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. Continuous loads usually require the branch circuit and overcurrent device to be sized at 125% of the load.
• Branch circuit: the circuit conductors between the final overcurrent device (the breaker or fuse) and the outlets.
• Feeder: conductors between the service equipment (or another power source) and the final branch-circuit overcurrent device.
• Service: the conductors and equipment that deliver energy from the utility to the premises wiring system.
• Outlet: a point on the wiring system where current is taken to supply equipment. A receptacle outlet, a lighting outlet and a smoke-alarm box are all outlets.
• Receptacle: a contact device installed at an outlet for the connection of an attachment plug. A duplex receptacle is two receptacles on one yoke.
• Grounded conductor: a system conductor that is intentionally grounded, usually the neutral (white or gray).
• Equipment grounding conductor (EGC): the conductive path that connects normally non-current-carrying metal parts together and back to the system grounded conductor or grounding electrode conductor (green, green-yellow or bare). It carries fault current, not normal current.
• Bonding (bonded): connected to establish electrical continuity and conductivity.
• Readily accessible: capable of being reached quickly, without climbing over obstacles, removing obstacles or using portable ladders.
• Qualified person: one who has the skills and knowledge related to the construction and operation of the equipment and has received safety training to recognise and avoid the hazards involved.
• Dwelling unit: a single unit providing complete and independent living facilities, including permanent provisions for living, sleeping, cooking and sanitation.
• Approved: acceptable to the authority having jurisdiction (AHJ), usually the electrical inspector.

Worked examples

Is it continuous? A store's display lighting runs from 9 a.m. to 9 p.m. Maximum current continues for more than three hours, so it is a continuous load. A 16 A continuous load needs a circuit rated at least 16 × 1.25 = 20 A.

Outlet or receptacle? A kitchen countertop has six duplex receptacles on one circuit. That is six receptacle outlets but twelve receptacles. Questions that ask "how many receptacles" and "how many outlets" have different answers.

Grounded vs grounding. On a 120 V circuit, current flows out on the black (ungrounded) conductor and back on the white (grounded) conductor. The bare copper (equipment grounding conductor) carries current only during a fault, long enough to trip the breaker. Mixing up "grounded" and "grounding" is one of the most common exam errors.

Readily accessible. A disconnect mounted above a ceiling tile, reachable only with a ladder, is accessible but not readily accessible. Rules that say "readily accessible" are not met.

Other general rules in Chapter 1

Article 110 sets requirements for every installation. A few you will use constantly:

• Equipment must be listed or labelled where required, and installed per its listing and instructions (110.3(B)).
• Work must be done in a "neat and workmanlike manner" (110.12).
• Terminations must respect conductor and terminal temperature ratings (110.14(C)), which affects conductor sizing.
• Working space in front of electrical equipment (110.26), so a person can work safely.

Common mistakes

• Using everyday meanings for defined words ("outlet" as a synonym for "receptacle").
• Forgetting the three-hour test for continuous loads, or applying 125% to a non-continuous load.
• Calling the neutral the "ground".
• Ignoring "readily" in "readily accessible".

Quick recap

Defined terms mean exactly what Article 100 says. Know ampacity, continuous load, branch circuit, feeder, service, outlet, receptacle, grounded conductor, equipment grounding conductor, bonding, readily accessible, qualified person and AHJ. Article 110 adds general rules for every job. Confirm wording in the edition your jurisdiction enforces (NFPA 70; checked on 2026-10-23).