Article 100 of the National Electrical Code (NEC) serves as the foundation for understanding and applying the Code effectively. It provides essential definitions for terms used throughout the NEC, ensuring clarity and consistency in electrical installations.
These definitions cover a wide range of topics, from safety devices like Arc-Fault Circuit Interrupters (AFCIs) to specialized equipment such as audio signal processing systems. By clearly defining key terms, Article 100 helps electricians, engineers, and inspectors communicate accurately and adhere to safety standards.
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Article 100 Definitions
Scope
Article 100 contains only those definitions essential to the application of the NEC. It excludes commonly defined general or technical terms from related codes and standards. Definitions specific to a particular article are indicated by the article number in parentheses.
Informational Note: Definitions followed by a reference in brackets are extracted from standards such as NFPA 30A, NFPA 75, NFPA 99, and others. Only editorial changes were made to align the text with the NEC.
Key Definitions
- Accessible (as applied to equipment):
Capable of being reached for operation, renewal, and inspection. (CMP—1) - Accessible (as applied to wiring methods):
Capable of being removed or exposed without damaging the building structure or finish, or not permanently closed in or blocked by the structure, other electrical equipment, other building systems, or finish of the building. (CMP—1) - Accessible, Readily (Readily Accessible):
Capable of being reached quickly for operation, renewal, or inspections 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, and so forth. (CMP—1)
Informational Note: Use of keys is a common practice under controlled or supervised conditions and a common alternative to the ready access requirements under such supervised conditions as provided elsewhere in the NEC. - Adapter:
A device used to adapt a circuit from one configuration of an attachment plug or receptacle to another configuration with the same current rating. (520) (CMP—15) - Adjustable Speed Drive:
Power conversion equipment that provides a means of adjusting the speed of an electric motor. (CMP—11)
Informational Note: A variable frequency drive is one type of electronic adjustable speed drive that controls the rotational speed of an AC electric motor by controlling the frequency and voltage of the electrical power supplied to the motor. - Adjustable Speed Drive System:
A combination of an adjustable speed drive, its associated motor(s), and auxiliary equipment. (CMP—11) - Aircraft Painting Hangar:
An aircraft hangar constructed for the express purpose of spraying, coating, and/or dipping applications and provided with dedicated ventilation supply and exhaust. (CMP—14) - Alternate Power Source:
One or more generator sets, or battery systems where permitted, intended to provide power during the interruption of the normal electrical service; or the public utility electrical service intended to provide power during interruption of service normally provided by the generating facilities on the premises. [99:3.3.4] (517) (CMP—15) - Ambulatory Health Care Occupancy:
An occupancy used to provide services or treatment simultaneously to four or more patients that provides, on an outpatient basis, one or more of the following:- Treatment for patients that renders the patients incapable of taking action for self-preservation under emergency conditions without the assistance of others.
- Anesthesia that renders the patients incapable of taking action for self-preservation under emergency conditions without the assistance of others.
- Treatment for patients who, due to the nature of their injury or illness, are incapable of taking action for self-preservation under emergency conditions without the assistance of others.
[101:3.3.198.1] (517) (CMP—15)
- Ampacity:
The maximum current, in amperes, that a conductor can carry continuously under the conditions of use without exceeding its temperature rating. (CMP—6) - Amplifier (Audio Amplifier) (Pre-Amplifier):
Electronic equipment that increases the current or voltage, or both, of an audio signal intended for use by another piece of audio equipment. Amplifier is the term used to denote an audio amplifier. (640) (CMP—12) - Appliance:
Utilization equipment, generally other than industrial, that is fastened in place, stationary, or portable; is normally built in a standardized size or type; and is installed or connected as a unit to perform one or more functions such as clothes washing, air-conditioning, food mixing, deep frying, and so forth. (CMP—17) - Applicator:
The device used to transfer energy between the output circuit and the object or mass to be heated. (665) (CMP—12) - Approved:
Acceptable to the authority having jurisdiction. (CMP—1) - Arc-Fault Circuit Interrupter (AFCI):
A device designed to protect against arc faults by recognizing arcing characteristics and de-energizing the circuit when an arc fault is detected. (CMP—2) - Array:
A mechanically and electrically integrated group of modules with support structures, including inverters, DC-to-DC converters, and associated wiring. (690) (CMP—4) - Askarel:
A generic term for nonflammable synthetic chlorinated hydrocarbons used as electrical insulating media. (CMP—9)
Informational Note: Askarels produce noncombustible hydrogen chloride under arcing conditions, but may also release combustible gases depending on the type. - Associated Apparatus:
Apparatus that affects the energy in intrinsically safe circuits and maintains intrinsic safety. It includes:- Electrical apparatus with alternative protection for hazardous locations.
- Electrical apparatus without protection, which must not be used in hazardous locations.
(CMP—14)
Informational Note No. 1: Associated apparatus has connections for intrinsically safe and nonintrinsically safe apparatus.
Informational Note No. 2: Examples include intrinsic safety barriers, which limit energy in hazardous locations.
Informational Note No. 3: Refer to ANSI/UL 913, ANSI/UL 60079-11, and ANSI/ISA RP 12.06.01 for additional information.
- Associated Nonincendive Field Wiring Apparatus:
Apparatus that affects energy in nonincendive field wiring circuits and maintains nonincendive energy levels. It includes:- Electrical apparatus with alternative protection for hazardous locations.
- Electrical apparatus without protection, which must not be used in hazardous locations.
(CMP—14)
Informational Note No. 1: This apparatus has connections for nonincendive field wiring and other electrical apparatus.
Informational Note No. 2: Refer to ANSI/UL 121201 for additional information.
- Attachment Fitting, Weight-Supporting (WSAF):
A device that connects utilization equipment conductors to branch-circuit conductors via a weight-supporting ceiling receptacle. (CMP—18)
Informational Note No. 1: Unlike attachment plugs, WSAFs do not use cords and support the weight of utilization equipment.
Informational Note No. 2: Refer to ANSI/NEMA WD 6 for standard configurations. - Attachment Plug (Plug Cap) (Plug):
A device that connects the conductors of a flexible cord to the conductors of a receptacle. (CMP—18) - Audio Autotransformer:
A transformer with a single winding and multiple taps for use with amplifier loudspeaker signal outputs. (640) (CMP—12) - Audio Signal Processing Equipment (Audio Equipment):
Equipment that produces or processes electronic signals for amplification and reproduction as acoustic signals within the human hearing range (20-20 kHz). (640) (CMP—12)
Informational Note: Includes loudspeakers, microphones, mixers, MIDI equipment, and audio playback devices. - Audio System:
The complete set of equipment and wiring used to create a functional audio signal processing, amplification, and reproduction system. (640) (CMP—12) - Audio Transformer:
A transformer with two or more electrically isolated windings and multiple taps for use with amplifier loudspeaker signal outputs. (640) (CMP—12) - Authority Having Jurisdiction (AHJ):
An organization or individual responsible for enforcing code requirements or approving equipment, materials, installations, or procedures. (CMP—1)
Informational Note: The AHJ can be a fire marshal, building official, electrical inspector, or other authorized entity. - Automatic:
Performing a function without human intervention. (CMP—1)
Referenced Standards
The definitions in Article 100 are aligned with the following NFPA standards:
- NFPA 30A—2021: Code for Motor Fuel Dispensing Facilities and Repair Garages
- NFPA 33—2021: Standard for Spray Application Using Flammable or Combustible Materials
- NFPA 75—2020: Standard for the Fire Protection of Information Technology Equipment
- NFPA 79—2021: Electrical Standard for Industrial Machinery
- NFPA 99—2021: Health Care Facilities Code
- NFPA 101®—2022: Life Safety Code®
- NFPA 110—2019: Standard for Emergency and Standby Power Systems
- NFPA 303—2021: Fire Protection Standard for Marinas and Boatyards
- NFPA 307—2021: Standard for the Construction and Fire Protection of Marine Terminals, Piers, and Wharves
- NFPA 499—2021: Recommended Practice for the Classification of Combustible Dusts and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas
- NFPA 501—2022: Standard on Manufactured Housing
- NFPA 790—2021: Standard for Competency of Third-Party Field Evaluation Bodies
- NFPA 1192—2021: Standard on Recreational Vehicles
Summary Table
| Term | Definition | Reference |
|---|---|---|
| Accessible (Equipment) | Capable of being reached for operation, renewal, and inspection. | CMP—1 |
| Accessible (Wiring Methods) | Capable of being removed or exposed without damaging the building structure or finish or not permanently closed in or blocked by the structure, other electrical equipment, other building systems, or finish of the building. | CMP—1 |
| Readily Accessible | Capable of being reached quickly for operation, renewal, or inspections 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, and so forth. | CMP—1 |
| Adapter | A device used to adapt a circuit from one configuration of an attachment plug or receptacle to another configuration with the same current rating. | 520, CMP—15 |
| Adjustable Speed Drive | Power conversion equipment that provides a means of adjusting the speed of an electric motor. | CMP—11 |
| Adjustable Speed Drive System | A combination of an adjustable speed drive, its associated motor(s), and auxiliary equipment. | CMP—11 |
| Aircraft Painting Hangar | An aircraft hangar constructed for the express purpose of spraying, coating, and/or dipping applications and provided with dedicated ventilation supply and exhaust. | CMP—14 |
| Alternate Power Source | One or more generator sets, or battery systems where permitted, intended to provide power during the interruption of the normal electrical service; or the public utility electrical service intended to provide power during interruption of service normally provided by the generating facilities on the premises. | [99:3.3.4], 517, CMP—15 |
| Ambulatory Health Care Occupancy | An occupancy used to provide services or treatment simultaneously to four or more patients that provides, on an outpatient basis, one or more of the following: Treatment for patients that renders the patients incapable of taking action for self-preservation under emergency conditions without the assistance of others; Anesthesia that renders the patients incapable of taking action for self-preservation under emergency conditions without the assistance of others; Treatment for patients who, due to the nature of their injury or illness, are incapable of taking action for self-preservation under emergency conditions without the assistance of others. | [101:3.3.198.1], 517, CMP—15 |
| Ampacity | The maximum current, in amperes, that a conductor can carry continuously under the conditions of use without exceeding its temperature rating. | CMP—6 |
| Amplifier | Electronic equipment that increases the current or voltage, or both, of an audio signal intended for use by another piece of audio equipment. Amplifier is the term used to denote an audio amplifier. | 640, CMP—12 |
| Appliance | Utilization equipment, generally other than industrial, that is fastened in place, stationary, or portable; is normally built in a standardized size or type; and is installed or connected as a unit to perform one or more functions such as clothes washing, air-conditioning, food mixing, deep frying, and so forth. | CMP—17 |
| Applicator | The device used to transfer energy between the output circuit and the object or mass to be heated. | 665, CMP—12 |
| Approved | Acceptable to the authority having jurisdiction. | CMP—1 |
| Term | Definition | Reference |
|---|---|---|
| Arc-Fault Circuit Interrupter (AFCI) | A device that detects arc faults and de-energizes the circuit. | CMP—2 |
| Array | A group of modules with support structures, inverters, and wiring. | 690, CMP—4 |
| Askarel | Nonflammable synthetic chlorinated hydrocarbons used as electrical insulating media. | CMP—9 |
| Associated Apparatus | Apparatus that affects energy in intrinsically safe circuits and maintains intrinsic safety. | CMP—14 |
| Associated Nonincendive Field Wiring Apparatus | Apparatus that affects energy in nonincendive field wiring circuits and maintains nonincendive energy levels. | CMP—14 |
| Attachment Fitting, Weight-Supporting (WSAF) | A device connecting utilization equipment to branch-circuit conductors via a weight-supporting ceiling receptacle. | CMP—18 |
| Attachment Plug (Plug Cap) (Plug) | A device connecting flexible cord conductors to receptacle conductors. | CMP—18 |
| Audio Autotransformer | A transformer with a single winding and multiple taps for amplifier loudspeaker signals. | 640, CMP—12 |
| Audio Signal Processing Equipment | Equipment that produces or processes audio signals for amplification and reproduction. | 640, CMP—12 |
| Audio System | The complete set of equipment and wiring for audio signal processing, amplification, and reproduction. | 640, CMP—12 |
| Audio Transformer | A transformer with isolated windings and multiple taps for amplifier loudspeaker signals. | 640, CMP—12 |
| Authority Having Jurisdiction (AHJ) | An organization or individual responsible for enforcing code requirements or approving equipment. | CMP—1 |
| Automatic | Performing a function without human intervention. | CMP—1 |