2017 NEC Definitions

Accessible (as applied to equipment).

Admitting close approach; not guarded by locked doors, elevation, or other effective means. (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 by the structure 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)

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)

Ampacity

The maximum current, in amperes, that a conductor can carry continuously under the conditions of use without exceeding its temperature rating. (CMP-6)

Appliance.

Utilization equipment, generally other than industrial, that is normally built in standardized sizes or types 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)

Approved

Acceptable to the authority having jurisdiction. (CMP-1)

Arc-Fault Circuit Interrupter (AFCI).

A device intended to provide protection from the effects of arc faults by recognizing characteristics unique to arcing and by functioning to de-energize the circuit when an arc fault is detected. (CMP-2)

Askarel

A generic term for a group of nonflammable synthetic chlorinated hydrocarbons used as electrical insulating media. (CMP-9)

Informational Note: Askarels of various compositional types are used. Under arcing conditions, the gases produced, while consisting predominantly of noncombustible hydrogen chloride, can include varying amounts of combustible gases, depending on the askarel type.

Associated Apparatus [as applied to Hazardous (Classified) Locations].

• Apparatus in which the circuits are not necessarily intrinsically safe themselves but that affects the energy in the intrinsically safe circuits and is relied on to maintain intrinsic safety. Such apparatus is one of the following:
• Electrical apparatus that has an alternative type of protection for use in the appropriate hazardous (classified) location

Electrical apparatus not so protected that shall not be used within a hazardous (classified) location

(CMP-14)

• Informational Note No. 1: Associated apparatus has identified intrinsically safe connections for intrinsically safe apparatus and also may have connections for nonintrinsically safe apparatus.
• Informational Note No. 2: An example of associated apparatus is an intrinsic safety barrier, which is a network designed to limit the energy (voltage and current) available to the protected circuit in the hazardous (classified) location, under specified fault conditions.

Associated Nonincendive Field Wiring Apparatus [as applied to Hazardous (Classified) Locations].

Apparatus in which the circuits are not necessarily nonincendive themselves but that affect the energy in nonincendive field wiring circuits and are relied upon to maintain nonincendive energy levels. Such apparatus are one of the following:Electrical apparatus that has an alternative type of protection for use in the appropriate hazardous (classified) locationElectrical apparatus not so protected that shall not be used in a hazardous (classified) location(CMP-14)Informational Note: Associated nonincendive field wiring apparatus has designated associated nonincendive field wiring apparatus connections for nonincendive field wiring apparatus and may also have connections for other electrical apparatus.

Attachment Plug (Plug Cap) (Plug).

A device that, by insertion in a receptacle, establishes a connection between the conductors of the attached flexible cord and the conductors connected permanently to the receptacle. (CMP-18)

Authority Having Jurisdiction (AHJ).

An organization, office, or individual responsible for enforcing the requirements of a code or standard, or for approving equipment, materials, an installation, or a procedure. (CMP-1)

Informational Note: The phrase “authority having jurisdiction,” or its acronym AHJ, is used in NFPA documents in a broad manner, since jurisdictions and approval agencies vary, as do their responsibilities. Where public safety is primary, the authority having jurisdiction may be a federal, state, local, or other regional department or individual such as a fire chief; fire marshal; chief of a fire prevention bureau, labor department, or health department; building official; electrical inspector; or others having statutory authority. For insurance purposes, an insurance inspection department, rating bureau, or other insurance company representative may be the authority having jurisdiction. In many circumstances, the property owner or his or her designated agent assumes the role of the authority having jurisdiction; at government installations, the commanding officer or departmental official may be the authority having jurisdiction.

Automatic.

Performing a function without the necessity of human intervention. (CMP-1)

Bathroom

An area including a basin with one or more of the following: a toilet, a urinal, a tub, a shower, a bidet, or similar plumbing fixtures. (CMP-2)

Battery System

Interconnected battery subsystems consisting of one or more storage batteries and battery chargers, and can include inverters, converters, and associated electrical equipment. (CMP-13)

Bonded (Bonding).

Connected to establish electrical continuity and conductivity. (CMP-5)

Bonding Conductor or Jumper

A reliable conductor to ensure the required electrical conductivity between metal parts required to be electrically connected. (CMP-5)

Either of the two terms bonding conductor or bonding jumper may be used. The term bonding jumper is sometimes interpreted to mean a short conductor, although some bonding jumpers may be several feet in length. The primary purpose of a bonding conductor or jumper is to ensure electrical conductivity between two conductive bodies, such as between a box and a metal raceway. Bonding jumpers are particularly important where a box has either concentric- or eccentric-type knockouts. These knockouts can impair the electrical conductivity between metal parts and may actually introduce unnecessary impedance into the grounding path.

Bonding Jumper, Equipment.

The connection between two or more portions of the equipment grounding conductor. (CMP-5)

Equipment bonding jumpers ensure that an effective ground-fault current path is not compromised by an interruption in mechanical or electrical continuity. For example, conduits entering an open-bottom switchboard are usually not mechanically connected to the switchboard. Expansion fittings may not provide electrical continuity because they are loosely joined raceways. Bonding jumpers are necessary in order to provide electrical continuity.

Bonding Jumper, Main.

The connection between the grounded circuit conductor and the equipment grounding conductor at the service. (CMP-5)

Branch Circuit.

The circuit conductors between the final overcurrent device protecting the circuit and the outlet(s). (CMP-2)

Branch Circuit, Appliance.

A branch circuit that supplies energy to one or more outlets to which appliances are to be connected and that has no permanently connected luminaires that are not a part of an appliance. (CMP-2)

Branch Circuit, General-Purpose.

A branch circuit that supplies two or more receptacles or outlets for lighting and appliances. (CMP-2)

Branch Circuit, Individual

A branch circuit that supplies only one utilization equipment. (CMP-2)

Branch Circuit, Multiwire.

A branch circuit that consists of two or more ungrounded conductors that have a voltage between them, and a grounded conductor that has equal voltage between it and each ungrounded conductor of the circuit and that is connected to the neutral or grounded conductor of the system. (CMP-2)

Building.

A structure that stands alone or that is separated from adjoining structures by fire walls. (CMP-1)

A building is generally considered to be a roofed or walled structure that is intended for supporting or sheltering any use or occupancy. However, a separate structure such as a pole, billboard sign, or water tower may also be considered to be a building. Definitions of the terms fire walls and fire doors are the responsibility of building codes. Generically, a fire wall may be defined as a wall that separates buildings or subdivides a building to prevent the spread of fire and that has a fire resistance rating and structural stability.

Cabinet

An enclosure that is designed for either surface mounting or flush mounting and is provided with a frame, mat, or trim in which a swinging door or doors are or can be hung. (CMP-9)

Cabinets are designed for surface or flush mounting with a trim to which a swinging door(s) is hung. A cutout box is designed for surface mounting with a swinging door(s) secured directly to the box. A panelboard is an electrical assembly designed to be placed in a cabinet or cutout box.

• Cable Routing Assembly
• A single channel or connected multiple channels, as well as associated fittings, forming a structural system that is used to support and route communications wires and cables, optical fiber cables, data cables associated with information technology and communications equipment, Class 2, Class 3, and Type PLTC cables, and power-limited fire alarm cables in plenum, riser, and general-purpose applications. (CMP-16)

Charge Controller.

Equipment that controls dc voltage or dc current, or both, and that is used to charge a battery or other energy storage device. (CMP-13)

Circuit Breaker

A device designed to open and close a circuit by nonautomatic means and to open the circuit automatically on a predetermined overcurrent without damage to itself when properly applied within its rating. (CMP-10)

Informational Note: The automatic opening means can be integral, direct acting with the circuit breaker, or remote from the circuit breaker.

Clothes Closet

A nonhabitable room or space intended primarily for storage of garments and apparel. (CMP-1)

Coaxial Cable

A cylindrical assembly composed of a conductor centered inside a metallic tube or shield, separated by a dielectric material, and usually covered by an insulating jacket. (CMP-16)

Combustible Dust [as applied to Hazardous (Classified) Locations]

Dust particles that are 500 microns or smaller (i.e., material passing a U.S. No. 35 Standard Sieve as defined in ASTM E11-2015, Standard Specification for Woven Wire Test Sieve Cloth and Test Sieves), and present a fire or explosion hazard when dispersed and ignited in air. (CMP-14)

Informational Note: See ASTM E1226-2012a, Standard Test Method for Explosibility of Dust Clouds, or ISO 6184-1, Explosion protection systems — Part 1: Determination of explosion indices of combustible dusts in air, for procedures for determining the explosibility of dusts.

Combustible Gas Detection System [as applied to Hazardous (Classified) Locations]

A protection technique utilizing stationary gas detectors in industrial establishments. (CMP-14)

Communications Equipment

The electronic equipment that performs the telecommunications operations for the transmission of audio, video, and data, and includes power equipment (e.g., dc converters, inverters, and batteries), technical support equipment (e.g., computers), and conductors dedicated solely to the operation of the equipment. (CMP-16)

Informational Note: As the telecommunications network transitions to a more data-centric network, computers, routers, servers, and their powering equipment, are becoming essential to the transmission of audio, video, and data and are finding increasing application in communications equipment installations.

Communications Raceway

An enclosed channel of nonmetallic materials designed expressly for holding communications wires and cables; optical fiber cables; data cables associated with information technology and communications equipment; Class 2, Class 3, and Type PLTC cables; and power-limited fire alarm cables in plenum, riser, and general-purpose applications. (CMP-16)

Composite Optical Fiber Cable

A cable containing optical fibers and current-carrying electrical conductors. (CMP-16)

Concealed

Rendered inaccessible by the structure or finish of the building. (CMP-1)

Informational Note: Wires in concealed raceways are considered concealed, even though they may become accessible by withdrawing them.

Raceways and cables supported or located within hollow frames or permanently enclosed by the finish of buildings are considered concealed. Raceways and cables in unfinished basements; in accessible underfloor areas or attics; or behind, above, or below panels designed to allow access; and that may be removed without damage to the building structure or finish are not considered concealed. See the definition of exposed (as applied to wiring methods).

Conductive Optical Fiber Cable

A factory assembly of one or more optical fibers having an overall covering and containing non–current-carrying conductive member(s) such as metallic strength member(s), metallic vapor barrier(s), metallic armor or metallic sheath. (CMP-16)

Conductor, Bare

A conductor having no covering or electrical insulation whatsoever. (CMP-6)

Conductor, Covered

A conductor encased within material of composition or thickness that is not recognized by this Code as electrical insulation. (CMP-6)

The uninsulated grounded system conductor within the overall exterior jacket of a Type SE cable is an example of a covered conductor. Covered conductors should always be treated as bare conductors for working clearances because the covering does not have a voltage rating, so the conductors are effectively uninsulated. See the definition of insulated conductor.

Conductor, Insulated

A conductor encased within material of composition and thickness that is recognized by this Code as electrical insulation. (CMP-6)

For the covering on a conductor to be considered insulation, it is generally required to pass minimum testing required by a product standard. One such product standard is UL 83, Thermoplastic-Insulated Wires and Cables. To meet the requirements of UL 83, specimens of finished single-conductor wires must pass specified tests that measure (1) resistance to flame propagation, (2) dielectric strength, even while immersed, and (3) resistance to abrasion, cracking, crushing, and impact. Only wires and cables that meet the minimum fire, electrical, and physical properties required by the applicable product standards are permitted to be marked with the letter designations found in Table 310.104(A). Unless a voltage rating is marked on the insulation, a conductor generally should be considered as a covered conductor. However, Class 2 conductors are not permitted to have a marked voltage rating.

Conduit Body

A separate portion of a conduit or tubing system that provides access through a removable cover(s) to the interior of the system at a junction of two or more sections of the system or at a terminal point of the system.

Boxes such as FS and FD or larger cast or sheet metal boxes are not classified as conduit bodies. (CMP-9)

Conduit bodies include the short-radius type as well as capped elbows and service-entrance elbows. Conduit bodies include the LB, LL, LR, C, T, and X designs.

Connector, Pressure (Solderless)

A device that establishes a connection between two or more conductors or between one or more conductors and a terminal by means of mechanical pressure and without the use of solder. (CMP-1)

Continuous Load

A load where the maximum current is expected to continue for 3 hours or more. (CMP-2)

Control Circuit

The circuit of a control apparatus or system that carries the electric signals directing the performance of the controller but does not carry the main power current. (CMP-11)

Control Drawing [as applied to Hazardous (Classified) Locations]

A drawing or other document provided by the manufacturer of the intrinsically safe or associated apparatus, or of the nonincendive field wiring apparatus or associated nonincendive field wiring apparatus, that details the allowed interconnections between the intrinsically safe and associated apparatus or between the nonincendive field wiring apparatus or associated nonincendive field wiring apparatus. (CMP-14)

Controller

A device or group of devices that serves to govern, in some predetermined manner, the electric power delivered to the apparatus to which it is connected. (CMP-1)

A controller may be a remote-controlled magnetic contactor, switch, circuit breaker, or other device that is normally used to start and stop motors and other apparatus. Stop-and-start stations and similar control circuit components that do not open the power conductors to the motor are not considered controllers.

Cooking Unit, Counter-Mounted

A cooking appliance designed for mounting in or on a counter and consisting of one or more heating elements, internal wiring, and built-in or mountable controls. (CMP-2)

Coordination, Selective (Selective Coordination)

Localization of an overcurrent condition to restrict outages to the circuit or equipment affected, accomplished by the selection and installation of overcurrent protective devices and their ratings or settings for the full range of available overcurrents, from overload to the maximum available fault current, and for the full range of overcurrent protective device opening times associated with those overcurrents. (CMP-10)


Fuses and circuit breakers have time/current characteristics that determine the time it takes to clear the fault for a given value of fault current. Selectivity occurs when the device closest to the fault opens before the next device upstream operates. Any fault on a branch circuit should open the branch-circuit breaker rather than the feeder overcurrent protection. All faults on a feeder should open the feeder overcurrent protection rather than the service overcurrent protection.

With coordinated overcurrent protection, the faulted or overloaded circuit is isolated by the selective operation of only the overcurrent protective device closest to the overcurrent condition. The main goal of selective coordination is to isolate the faulted portion of the electrical circuit quickly while at the same time maintaining power to the remainder of the electrical system. The electrical system overcurrent protection must guard against short circuits and ground faults to ensure that the resulting damage is minimized while other parts of the system not directly involved with the fault are kept operational until other protective devices clear the fault. Where a series-rated system is used, an upstream device in the series will operate to protect a downstream device. For example, a current-limiting fuse will limit the available fault current to the downstream circuit breaker.

Copper-Clad Aluminum Conductors

Conductors drawn from a copper-clad aluminum rod, with the copper metallurgically bonded to an aluminum core, where the copper forms a minimum of 10 percent of the cross-sectional area of a solid conductor or each strand of a stranded conductor. (CMP-6)

Cord Connector [as applied to Hazardous (Classified) Locations]

A fitting intended to terminate a cord to a box or similar device and reduce the strain at points of termination and may include an explosionproof, a dust-ignitionproof, or a flameproof seal. (CMP-14)

Types TC-ER and TC-ER-HL as a wiring method in Articles 501, 502, 503, 505, and 506 require a method of termination that currently is identified as a cord connector in the hazardous location (HazLoc) industry. However, the wiring device industry also uses the term cord connector to refer to a female electrical connector. The differentiation is addressed by use of the denotation “[as applied to hazardous (classified) locations].”

Cutout Box

An enclosure designed for surface mounting that has swinging doors or covers secured directly to and telescoping with the walls of the enclosure. (CMP-9)

Dead Front

Without live parts exposed to a person on the operating side of the equipment. (CMP-9)

Demand Factor

The ratio of the maximum demand of a system, or part of a system, to the total connected load of a system or the part of the system under consideration. (CMP-2)

Device

A unit of an electrical system, other than a conductor, that carries or controls electric energy as its principal function. (CMP-1)

Switches, circuit breakers, fuseholders, receptacles, attachment plugs, and lampholders that distribute or control but do not consume electrical energy are considered devices. Devices that consume incidental amounts of electrical energy in the performance of carrying or controlling electricity—such as a switch or a receptacle with an internal pilot light or a magnetic contactor—are considered devices and not utilization equipment. Although conductors are units of the electrical system, they are not devices.

Disconnecting Means

A device, or group of devices, or other means by which the conductors of a circuit can be disconnected from their source of supply. (CMP-1)

Dust-Ignitionproof [as applied to Hazardous (Classified) Locations]

Equipment enclosed in a manner that excludes dusts and does not permit arcs, sparks, or heat otherwise generated or liberated inside of the enclosure to cause ignition of exterior accumulations or atmospheric suspensions of a specified dust on or in the vicinity of the enclosure. (CMP-14)

Informational Note: For further information on dust-ignitionproof enclosures, see ANSI/UL 1202-2013,Enclosures for Electrical Equipment, and ANSI/UL 1203-2013, Explosionproof and Dust-Ignitionproof Electrical Equipment for Hazardous (Classified) Locations.

Dusttight

Enclosures constructed so that dust will not enter under specified test conditions. (CMP-14)

• Informational Note No. 1: Enclosure Types 3, 3S, 3SX, 4, 4X, 5, 6, 6P, 12, 12K, and 13, per ANSI/NEMA 250-2014, Enclosures for Electrical Equipment, are considered dusttight and suitable for use in unclassified locations and in Class II, Division 2; Class III; and Zone 22 hazardous (classified) locations.
• Informational Note No. 2: For further information, see ANSI/ISA-12.12.01-2013, Nonincendive Electrical Equipment for Use in Class I and II, Division 2, and Class III, Divisions 1 and 2 Hazardous (Classified) Locations.

Some dusttight constructions are only for wind-blown dust and may not be designed for combustible dusts found in Class II hazardous locations. The basic standard used to investigate dusttight enclosures for Class II, Division 2 locations is UL 1604, Electrical Equipment for Use in Class I and II, Division 2 and Class III Hazardous (Classified) Locations. A dusttight enclosure has been determined to exclude dust under specified test conditions. Combustible dust is 500 microns or smaller. The AHJ determines the suitability of a dusttight enclosure or the acceptance of a specific standard, test, or listing organization.

Duty, Continuous

Operation at a substantially constant load for an indefinitely long time. (CMP-1)

Duty, Intermittent

Operation for alternate intervals of (1) load and no load; or (2) load and rest; or (3) load, no load, and rest. (CMP-1)

Duty, Periodic

Intermittent operation in which the load conditions are regularly recurrent. (CMP-1)

Duty, Short-Time

Operation at a substantially constant load for a short and definite, specified time. (CMP-1)

Duty, Varying

Operation at loads, and for intervals of time, both of which may be subject to wide variation. (CMP-1)

Dwelling, One-Family

A building that consists solely of one dwelling unit. (CMP-1)

Dwelling, Two-Family

A building that consists solely of two dwelling units. (CMP-1)

Dwelling, Multifamily

A building that contains three or more dwelling units. (CMP-1)

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. (CMP-2)

Where dwelling units are referenced throughout the NEC, rooms in motels, hotels, and similar occupancies that have permanent provisions for living, sleeping, cooking, and sanitation are also classified as dwelling units.

Effective Ground-Fault Current Path

An intentionally constructed, low-impedance electrically conductive path designed and intended to carry current under ground-fault conditions from the point of a ground fault on a wiring system to the electrical supply source and that facilitates the operation of the overcurrent protective device or ground-fault detectors. (CMP-5)

Electric Power Production and Distribution Network

Power production, distribution, and utilization equipment and facilities, such as electric utility systems that deliver electric power to the connected loads, that are external to and not controlled by an interactive system. (CMP-13)

Electric Sign

A fixed, stationary, or portable self-contained, electrically operated and/or electrically illuminated utilization equipment with words or symbols designed to convey information or attract attention. (CMP-18)

Electric-Discharge Lighting

Systems of illumination utilizing fluorescent lamps, high-intensity discharge (HID) lamps, or neon tubing. (CMP-18)

Electrical Circuit Protective System

A system consisting of components and materials intended for installation as protection for specific electrical wiring systems with respect to the disruption of electrical circuit integrity upon exterior fire exposure. (CMP-16)

Electronically Actuated Fuse

An overcurrent protective device that generally consists of a control module that provides current-sensing, electronically derived time–current characteristics, energy to initiate tripping, and an interrupting module that interrupts current when an overcurrent occurs. Such fuses may or may not operate in a current-limiting fashion, depending on the type of control selected. (CMP-10)

Enclosed

Surrounded by a case, housing, fence, or wall(s) that prevents persons from accidentally contacting energized parts. (CMP-1)

Enclosure

The case or housing of apparatus, or the fence or walls surrounding an installation to prevent personnel from accidentally contacting energized parts or to protect the equipment from physical damage. (CMP-1)

Informational Note: See Table 110.28 for examples of enclosure types.

Energized

Electrically connected to, or is, a source of voltage. (CMP-1)

The term energized is not limited to equipment that is “connected to a source of voltage.” Equipment such as batteries, capacitors, and conductors with induced voltages must also be considered energized.

Equipment

A general term, including fittings, devices, appliances, luminaires, apparatus, machinery, and the like used as a part of, or in connection with, an electrical installation. (CMP-1)

Explosionproof Equipment

Equipment enclosed in a case that is capable of withstanding an explosion of a specified gas or vapor that may occur within it and of preventing the ignition of a specified gas or vapor surrounding the enclosure by sparks, flashes, or explosion of the gas or vapor within, and that operates at such an external temperature that a surrounding flammable atmosphere will not be ignited thereby. (CMP-14)

Informational Note: For further information, see ANSI/UL 1203-2009, Explosion-Proof and Dust-Ignition-Proof Electrical Equipment for Use in Hazardous (Classified) Locations.

Exposed (as applied to live parts)

Capable of being inadvertently touched or approached nearer than a safe distance by a person. (CMP-1)

Informational Note: This term applies to parts that are not suitably guarded, isolated, or insulated.

Exposed (as applied to wiring methods)

On or attached to the surface or behind panels designed to allow access. (CMP-1)

Externally Operable

Capable of being operated without exposing the operator to contact with live parts. (CMP-1)

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. (CMP-2)

Festoon Lighting

A string of outdoor lights that is suspended between two points. (CMP-18)

Field Evaluation Body (FEB)

An organization or part of an organization that performs field evaluations of electrical or other equipment. [790, 2012] (CMP-1)

Field Labeled (as applied to evaluated products)

Equipment or materials to which has been attached a label, symbol, or other identifying mark of an FEB indicating the equipment or materials were evaluated and found to comply with requirements as described in an accompanying field evaluation report. (CMP-1)

Fitting

An accessory such as a locknut, bushing, or other part of a wiring system that is intended primarily to perform a mechanical rather than an electrical function. (CMP-1)

Conduit bodies and couplings, electrical metallic tubing (EMT) connectors and couplings, and threadless connectors are considered fittings.

Garage

A building or portion of a building in which one or more self-propelled vehicles can be kept for use, sale, storage, rental, repair, exhibition, or demonstration purposes. (CMP-1)

Informational Note: For commercial garages, repair and storage, see Article 511.

Ground

The earth. (CMP-5)

Ground Fault

An unintentional, electrically conductive connection between an ungrounded conductor of an electrical circuit and the normally non–current-carrying conductors, metallic enclosures, metallic raceways, metallic equipment, or earth. (CMP-5)

Grounded (Grounding)

Connected (connecting) to ground or to a conductive body that extends the ground connection. (CMP-5)

Grounded, Solidly

Connected to ground without inserting any resistor or impedance device. (CMP-5)

Grounded Conductor

A system or circuit conductor that is intentionally grounded. (CMP-5)

Ground-Fault Circuit Interrupter (GFCI)

A device intended for the protection of personnel that functions to de-energize a circuit or portion thereof within an established period of time when a current to ground exceeds the values established for a Class A device. (CMP-2)

Informational Note: Class A ground-fault circuit interrupters trip when the current to ground is 6 mA or higher and do not trip when the current to ground is less than 4 mA. For further information, see UL 943, Standard for Ground-Fault Circuit Interrupters.

Ground-Fault Current Path

An electrically conductive path from the point of a ground fault on a wiring system through normally non–current-carrying conductors, equipment, or the earth to the electrical supply source. (CMP-5)

Informational Note: Examples of ground-fault current paths are any combination of equipment grounding conductors, metallic raceways, metallic cable sheaths, electrical equipment, and any other electrically conductive material such as metal, water, and gas piping; steel framing members; stucco mesh; metal ducting; reinforcing steel; shields of communications cables; and the earth itself.

Ground-Fault Protection of Equipment

A system intended to provide protection of equipment from damaging line-to-ground fault currents by operating to cause a disconnecting means to open all ungrounded conductors of the faulted circuit. This protection is provided at current levels less than those required to protect conductors from damage through the operation of a supply circuit overcurrent device. (CMP-5)

Grounding Conductor, Equipment (EGC)

The conductive path(s) that provides a ground-fault current path and connects normally non–current-carrying metal parts of equipment together and to the system grounded conductor or to the grounding electrode conductor, or both. (CMP-5)

• Informational Note No. 1: It is recognized that the equipment grounding conductor also performs bonding.
• Informational Note No. 2: See 250.118 for a list of acceptable equipment grounding conductors.

Grounding Electrode

A conducting object through which a direct connection to earth is established. (CMP-5)

Grounding Electrode Conductor

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. (CMP-5)

Guarded

Covered, shielded, fenced, enclosed, or otherwise protected by means of suitable covers, casings, barriers, rails, screens, mats, or platforms to remove the likelihood of approach or contact by persons or objects to a point of danger. (CMP-1)

Guest Room

An accommodation combining living, sleeping, sanitary, and storage facilities within a compartment. (CMP-2)

Guest Suite

An accommodation with two or more contiguous rooms comprising a compartment, with or without doors between such rooms, that provides living, sleeping, sanitary, and storage facilities. (CMP-2)

If a guest room or guest suite contains permanent provisions for cooking, dwelling unit requirements apply.

Handhole Enclosure

An enclosure for use in underground systems, provided with an open or closed bottom, and sized to allow personnel to reach into, but not enter, for the purpose of installing, operating, or maintaining equipment or wiring or both. (CMP-9)

Hermetic Refrigerant Motor-Compressor

A combination consisting of a compressor and motor, both of which are enclosed in the same housing, with no external shaft or shaft seals, with the motor operating in the refrigerant. (CMP-11)

Hermetically Sealed [as applied to Hazardous (Classified) Locations]

Equipment sealed against the entrance of an external atmosphere where the seal is made by fusion, for example, soldering, brazing, welding, or the fusion of glass to metal. (CMP-14)

Informational Note: For further information, see ANSI/ISA-12.12.01-2013, Nonincendive Electrical Equipment for Use in Class I and II, Division 2, and Class III, Divisions 1 and 2 Hazardous (Classified) Locations.

Hoistway

Any shaftway, hatchway, well hole, or other vertical opening or space in which an elevator or dumbwaiter is designed to operate. (CMP-12).

Hybrid System

A system comprised of multiple power sources. These power sources could include photovoltaic, wind, micro-hydro generators, engine-driven generators, and others, but do not include electric power production and distribution network systems. Energy storage systems such as batteries, flywheels, or superconducting magnetic storage equipment do not constitute a power source for the purpose of this definition. The energy regenerated by an overhauling (descending) elevator does not constitute a power source for the purpose of this definition. (CMP-4)

Identified (as applied to equipment)

Recognizable as suitable for the specific purpose, function, use, environment, application, and so forth, where described in a particular Code requirement. (CMP-1)

Informational Note: Some examples of ways to determine suitability of equipment for a specific purpose, environment, or application include investigations by a qualified testing laboratory (listing and labeling), an inspection agency, or other organizations concerned with product evaluation.

In Sight From (Within Sight From, Within Sight)

Where this Code specifies that one equipment shall be “in sight from,” “within sight from,” or “within sight of,” and so forth, another equipment, the specified equipment is to be visible and not more than 15 m (50 ft) distant from the other. (CMP-1)

Industrial Control Panel

An assembly of two or more components consisting of one of the following: (1) power circuit components only, such as motor controllers, overload relays, fused disconnect switches, and circuit breakers; (2) control circuit components only, such as push buttons, pilot lights, selector switches, timers, switches, and control relays; (3) a combination of power and control circuit components. These components, with associated wiring and terminals, are mounted on, or contained within, an enclosure or mounted on a subpanel.

The industrial control panel does not include the controlled equipment. (CMP-11)

Information Technology Equipment (ITE)

Equipment and systems rated 1000 volts or less, normally found in offices or other business establishments and similar environments classified as ordinary locations, that are used for creation and manipulation of data, voice, video, and similar signals that are not communications equipment as defined in Part I of Article 100 and do not process communications circuits as defined in 800.2. (CMP-12)

Informational Note: For information on listing requirements for both information technology equipment and communications equipment, see UL 60950-1-2014, Information Technology Equipment — Safety — Part 1: General Requirementsor UL 62368-1-2014, Audio/Video Information and Communication Technology Equipment Part 1: Safety Requirements.

Innerduct

A nonmetallic raceway placed within a larger raceway. (CMP-16)

Utility-Interactive Inverter \ Interactive Inverter

An inverter intended for use in parallel with an electric utility to supply common loads that may deliver power to the utility. (CMP-13)

The most common interactive inverters are string inverters and microinverters. String inverters are typically connected to a number of photovoltaic (PV) modules. Microinverters are usually connected to a single module. If microinverters are used in an installation, each module will have its own microinverter. String inverters and microinverters can both be interactive.

Interactive System

An electric power production system that is operating in parallel with and capable of delivering energy to an electric primary source supply system. (CMP-4)

Interrupting Rating

The highest current at rated voltage that a device is identified to interrupt under standard test conditions. (CMP-10)

Informational Note: Equipment intended to interrupt current at other than fault levels may have its interrupting rating implied in other ratings, such as horsepower or locked rotor current.

Interrupting ratings are essential for the coordination of electrical systems. The exhibit below depicts the label of a 225-ampere frame circuit breaker, showing the interrupting capacity ratings. See the definition of short-circuit current rating.

Intersystem Bonding Termination

A device that provides a means for connecting intersystem bonding conductors for communications systems to the grounding electrode system.(CMP-16)

Intrinsically Safe Apparatus

Apparatus in which all the circuits are intrinsically safe. (CMP-14)

Is designed to be incapable of producing heat or spark sufficient to ignite an explosive atmosphere, even if the device has experienced deterioration or has been damaged.

Intrinsically Safe System [as applied to Hazardous (Classified) Locations]

An assembly of interconnected intrinsically safe apparatus, associated apparatus, and interconnecting cables, in that those parts of the system that may be used in hazardous (classified) locations are intrinsically safe circuits. (CMP-14)

Informational Note: An intrinsically safe system may include more than one intrinsically safe circuit.

Isolated (as applied to location)

Not readily accessible to persons unless special means for access are used. (CMP-1)

Kitchen

An area with a sink and permanent provisions for food preparation and cooking. (CMP-2)

Labeled

Equipment or materials to which has been attached a label, symbol, or other identifying mark of an organization that is acceptable to the authority having jurisdiction and concerned with product evaluation, that maintains periodic inspection of production of labeled equipment or materials, and by whose labeling the manufacturer indicates compliance with appropriate standards or performance in a specified manner. (CMP-1)

Equipment and conductors required or permitted by the NEC are acceptable only if they have been approved for a specific environment or application by the AHJ as stated in 110.2. Listing or labeling by a qualified testing laboratory provides a basis for approval.

Lighting Outlet

An outlet intended for the direct connection of a lampholder or luminaire. (CMP-18)

Lighting Track (Track Lighting)

A manufactured assembly designed to support and energize luminaires that are capable of being readily repositioned on the track. Its length can be altered by the addition or subtraction of sections of track.(CMP-18)

Listed

Equipment, materials, or services included in a list published by an organization that is acceptable to the authority having jurisdiction and concerned with evaluation of products or services, that maintains periodic inspection of production of listed equipment or materials or periodic evaluation of services, and whose listing states that either the equipment, material, or service meets appropriate designated standards or has been tested and found suitable for a specified purpose. (CMP-1)

Informational Note: The means for identifying listed equipment may vary for each organization concerned with product evaluation, some of which do not recognize equipment as listed unless it is also labeled. Use of the system employed by the listing organization allows the authority having jurisdiction to identify a listed product.

Live Parts

Energized conductive components. (CMP-1)

Location, Damp

Locations protected from weather and not subject to saturation with water or other liquids but subject to moderate degrees of moisture. (CMP-1)

Informational Note: Examples of such locations include partially protected locations under canopies, marquees, roofed open porches, and like locations, and interior locations subject to moderate degrees of moisture, such as some basements, some barns, and some cold-storage warehouses.

Location, Dry

A location not normally subject to dampness or wetness. A location classified as dry may be temporarily subject to dampness or wetness, as in the case of a building under construction. (CMP-1)

Location, Wet

Installations underground or in concrete slabs or masonry in direct contact with the earth; in locations subject to saturation with water or other liquids, such as vehicle washing areas; and in unprotected locations exposed to weather. (CMP-1)

Both the inside of a raceway in a wet location and a raceway installed underground are considered wet locations. Therefore, any conductors inside the raceway would be required to be suitable for wet locations.

Luminaire

A complete lighting unit consisting of a light source such as a lamp or lamps, together with the parts designed to position the light source and connect it to the power supply. It may also include parts to protect the light source or the ballast or to distribute the light. A lampholder itself is not a luminaire. (CMP-18)

Light pipes and glass fiber optics are sometimes referred to as “lighting systems.” The definition of luminaire includes such systems, because light pipes and fiber optics are actually “parts designed to distribute the light.”

Mobile Equipment

Equipment with electrical components suitable to be moved only with mechanical aids or is provided with wheels for movement by person(s) or powered devices. (CMP-14)

Motor Control Center

An assembly of one or more enclosed sections having a common power bus and principally containing motor control units. (CMP-11)

Multioutlet Assembly

A type of surface, flush, or freestanding raceway designed to hold conductors and receptacles, assembled in the field or at the factory. (CMP-18)

Multioutlet assemblies include freestanding assemblies with multiple receptacles, commonly called power poles. In dry locations, metal and nonmetallic multioutlet assemblies are permitted; however, they are not permitted to be installed if concealed. Portable assemblies, often called “power strips” or “plug strips,” are not multioutlet assemblies but are “relocatable power taps.”

Neutral Conductor

The conductor connected to the neutral point of a system that is intended to carry current under normal conditions. (CMP-5)

The neutral conductor is a current-carrying conductor that is not safe to work on while energized.

Neutral Point

The common point on a wye-connection in a polyphase system or midpoint on a single-phase, 3-wire system, or midpoint of a single-phase portion of a 3-phase delta system, or a midpoint of a 3-wire, direct-current system. (CMP-5)

Informational Note: At the neutral point of the system, the vectorial sum of the nominal voltages from all other phases within the system that utilize the neutral, with respect to the neutral point, is zero potential.

Nonautomatic

Requiring human intervention to perform a function. (CMP-1)

Nonconductive Optical Fiber Cable

A factory assembly of one or more optical fibers having an overall covering and containing no electrically conductive materials. (CMP-16)

Nonincendive Circuit [as applied to Hazardous (Classified) Locations]

A circuit, other than field wiring, in which any arc or thermal effect produced under intended operating conditions of the equipment, is not capable, under specified test conditions, of igniting the flammable gas–air, vapor–air, or dust–air mixture. (CMP-14)

Informational Note: Conditions are described in ANSI/ISA-12.12.01-2013, Nonincendive Electrical Equipment for Use in Class I and II, Division 2, and Class III, Divisions 1 and 2 Hazardous (Classified) Locations.

A nonincendive circuit employs a protection technique that prevents electrical circuits from causing a fire or explosion in a hazardous location under normal conditions. This is in contrast to an intrinsically safe circuit, whose evaluation is conducted under abnormal conditions. Because of its definition, a nonincendive circuit is a low-energy circuit, but many low-voltage, low-energy circuits, including some communications circuits and thermocouple circuits (or Class 2 or 3 circuits as defined in Article 725), are not necessarily nonincendive.

Nonincendive Component [as applied to Hazardous (Classified) Locations]

A component having contacts for making or breaking an incendive circuit and the contacting mechanism is constructed so that the component is incapable of igniting the specified flammable gas–air or vapor–air mixture. The housing of a nonincendive component is not intended to exclude the flammable atmosphere or contain an explosion. (CMP-14)

Informational Note: For further information, see ANSI/ISA-12.12.01-2013, Nonincendive Electrical Equipment for Use in Class I and II, Division 2, and Class III, Divisions 1 and 2 Hazardous (Classified) Locations.

Nonincendive Equipment [as applied to Hazardous (Classified) Locations]

Equipment having electrical/electronic circuitry that is incapable, under normal operating conditions, of causing ignition of a specified flammable gas–air, vapor–air, or dust–air mixture due to arcing or thermal means. (CMP-14)

Informational Note: For further information, see ANSI/ISA-12.12.01-2013, Nonincendive Electrical Equipment for Use in Class I and II, Division 2, and Class III, Divisions 1 and 2 Hazardous (Classified) Locations.

Nonincendive Field Wiring [as applied to Hazardous (Classified) Locations]

Wiring that enters or leaves an equipment enclosure and, under normal operating conditions of the equipment, is not capable, due to arcing or thermal effects, of igniting the flammable gas–air, vapor–air, or dust–air mixture. Normal operation includes opening, shorting, or grounding the field wiring. (CMP-14)

Field wiring meeting this definition requires limitations of energy under normally expected conditions of operation, such as opening, shorting, or grounding. For example, stored energy in the form of mutual inductance or capacitance could be released during an opening, shorting, or grounding of nonincendive field wiring, which defeats the purpose of this protection technique.

Nonincendive Field Wiring Apparatus [as applied to Hazardous (Classified) Locations]

Apparatus intended to be connected to nonincendive field wiring. (CMP-14)

Informational Note: For further information, see ANSI/ISA-12.12.01-2013, Nonincendive Electrical Equipment for Use in Class I and II, Division 2, and Class III, Divisions 1 and 2 Hazardous (Classified) Locations.

Nonlinear Load

A load where the wave shape of the steady-state current does not follow the wave shape of the applied voltage. (CMP-1)

Informational Note: Electronic equipment, electronic/electric-discharge lighting, adjustable-speed drive systems, and similar equipment may be nonlinear loads.

Nonlinear loads are a major cause of harmonic currents. Additional conductor heating is just one of the undesirable operational effects associated with harmonic currents. Informational Note No. 1(2) following 310.15(A)(3) points out that harmonic current is one of the factors that must be considered when determining the heat generated internally in a conductor.

Actual circuit measurements of current for nonlinear loads should be made using only true rms-measuring ammeter instruments. Averaging ammeters produces inaccurate values if used to measure nonlinear loads.

Oil Immersion [as applied to Hazardous (Classified) Locations]

Electrical equipment immersed in a protective liquid in such a way that an explosive atmosphere that may be above the liquid or outside the enclosure cannot be ignited. (CMP-14)

Optical Fiber Cable

A factory assembly or field assembly of one or more optical fibers having an overall covering. (CMP-16)

Informational Note: A field-assembled optical fiber cable is an assembly of one or more optical fibers within a jacket. The jacket, without optical fibers, is installed in a manner similar to conduit or raceway. Once the jacket is installed, the optical fibers are inserted into the jacket, completing the cable assembly.

Outlet

A point on the wiring system at which current is taken to supply utilization equipment. (CMP-1)

The term outlet is frequently misused to refer to receptacles. Although receptacle outlets are outlets, not all outlets are receptacle outlets. Other common examples of outlets include lighting outlets and smoke alarm outlets

Outline Lighting

An arrangement of incandescent lamps, electric-discharge lighting, or other electrically powered light sources to outline or call attention to certain features such as the shape of a building or the decoration of a window. (CMP-18)

Outline lighting includes low-voltage, light-emitting diodes as well as other luminaires installed to form various shapes.

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. (CMP-10)

Informational Note: A current in excess of rating may be accommodated by certain equipment and conductors for a given set of conditions. Therefore, the rules for overcurrent protection are specific for particular situations.

Overcurrent Protective Device, Branch-Circuit

A device capable of providing protection for service, feeder, and branch circuits and equipment over the full range of overcurrents between its rated current and its interrupting rating. Such devices are provided with interrupting ratings appropriate for the intended use but no less than 5000 amperes. (CMP-10)

The protection provided may be overload, short-circuit, or ground-fault, or a combination, depending on the application.

Overcurrent Protective Device, Supplementary

A device intended to provide limited overcurrent protection for specific applications and utilization equipment such as luminaires and appliances. This limited protection is in addition to the protection provided in the required branch circuit by the branch-circuit overcurrent protective device. (CMP-10)

The definition of supplementary overcurrent protective device makes two important distinctions between overcurrent protective devices. First, the use of a supplementary device is specifically limited to a few applications. Second, where it is used, the supplementary device must be in addition to and protected by the more robust branch-circuit overcurrent protective device.

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. (CMP-10)

Panelboard

A single panel or group of panel units designed for assembly in the form of a single panel, including buses and automatic overcurrent devices, and equipped with or without switches for the control of light, heat, or power circuits; designed to be placed in a cabinet or cutout box placed in or against a wall, partition, or other support; and accessible only from the front. (CMP-9)

Photovoltaic (PV) System

The total components and subsystem that, in combination, convert solar energy into electric energy for connection to a utilization load. (CMP-4)

Plenum

A compartment or chamber to which one or more air ducts are connected and that forms part of the air distribution system. (CMP-3)

Because of concerns about the transfer of products of combustion through environmental air systems, the NEC provides specific requirements—in 300.22(B), (C), and (D) and in Articles 725, 760, 770, 800, 820, 830, and 840—for the installation of wiring methods that are subject to the direct flow of environmental air. The NEC definition of the term plenum is similar to the definition of plenum contained in NFPA 90A, Standard for the Installation of Air-Conditioning and Ventilating Systems. The definition is used in conjunction with the requirements for the installation of wiring methods in spaces used for air transfer that are not specifically fabricated as ducts for environmental air.

Portable Equipment

Equipment with electrical components suitable to be moved by a single person without mechanical aids. (CMP-14)

Power Outlet

An enclosed assembly that may include receptacles, circuit breakers, fuseholders, fused switches, buses, and watt-hour meter mounting means; intended to supply and control power to mobile homes, recreational vehicles, park trailers, or boats or to serve as a means for distributing power required to operate mobile or temporarily installed equipment.(CMP-19)

Premises Wiring (System)

Interior and exterior wiring, including power, lighting, control, and signal circuit wiring together with all their associated hardware, fittings, and wiring devices, both permanently and temporarily installed. This includes (a) wiring from the service point or power source to the outlets or (b) wiring from and including the power source to the outlets where there is no service point.

Such wiring does not include wiring internal to appliances, luminaires, motors, controllers, motor control centers, and similar equipment. (CMP-1)

Informational Note: Power sources include, but are not limited to, interconnected or stand-alone batteries, solar photovoltaic systems, other distributed generation systems, or generators.

A premises wiring system does not have to be supplied by an electric utility. For example, portable generators and stand-alone photovoltaic systems can supply premises wiring systems. If there is no service point, there are no service conductors. The supply conductors are feeder conductors.

Pressurized [as applied to Hazardous (Classified) Locations]

The process of supplying an enclosure with a protective gas with or without continuous flow, at sufficient pressure to prevent the entrance of combustible dust or ignitible fibers/flyings. (CMP-14)

Process Seal [as applied to Hazardous (Classified) Locations]

A seal between electrical systems and flammable or combustible process fluids where a failure could allow the migration of process fluids into the premises’ wiring system. (CMP-14)

Purged and Pressurized [as applied to Hazardous (Classified) Locations]

The process of (1) purging, supplying an enclosure with a protective gas at a sufficient flow and positive pressure to reduce the concentration of any flammable gas or vapor initially present to an acceptable level; and (2) pressurization, supplying an enclosure with a protective gas with or without continuous flow at sufficient pressure to prevent the entrance of a flammable gas or vapor, a combustible dust, or an ignitible fiber. (CMP-14)

Informational Note: For further information, see ANSI/NFPA 496-2013, Purged and Pressurized Enclosures for Electrical Equipment.

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. (CMP-1)

Informational Note: Refer to NFPA 70E-2012, Standard for Electrical Safety in the Workplace, for electrical safety training requirements.

Raceway

An enclosed channel designed expressly for holding wires, cables, or busbars, with additional functions as permitted in this Code. (CMP-8)

Informational Note: A raceway is identified within specific article definitions.

Cable trays are support systems for wiring methods and are not considered to be raceways.

Rainproof

Constructed, protected, or treated so as to prevent rain from interfering with the successful operation of the apparatus under specified test conditions. (CMP-1)

Raintight

Constructed or protected so that exposure to a beating rain will not result in the entrance of water under specified test conditions. (CMP-1)

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. A multiple receptacle is two or more contact devices on the same yoke. (CMP-18)

Receptacle Outlet

An outlet where one or more receptacles are installed. (CMP-18)

Remote-Control Circuit

Any electrical circuit that controls any other circuit through a relay or an equivalent device. (CMP-3)

Retrofit Kit

A general term for a complete subassembly of parts and devices for field conversion of utilization equipment. (CMP-18)

Sealable Equipment

Equipment enclosed in a case or cabinet that is provided with a means of sealing or locking so that live parts cannot be made accessible without opening the enclosure. (CMP-1)

Informational Note: The equipment may or may not be operable without opening the enclosure.

Separately Derived System

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. (CMP-5)

Examples of separately derived systems include generators, batteries, converter windings, transformers, and solar photovoltaic systems, provided they have no direct electrical connection to another source. The earth, metal enclosures, metal raceways, and equipment grounding conductors may provide incidental connection between systems. In addition, 250.30(A)(6) permits a common grounding electrode conductor to be installed for multiple separately derived systems. This definition clarifies that those systems can still be considered to be separately derived systems as long as the separately derived systems have no direct electrical connection to service-derived systems.

Service

The conductors and equipment for delivering electric energy from the serving utility to the wiring system of the premises served. (CMP-4)

A service can only be supplied by the serving utility. If electric energy is supplied by other than the serving utility, the supplied conductors and equipment are considered feeders and not a service.

Service Cable

Service conductors made up in the form of a cable. (CMP-4)

Service Conductors

The conductors from the service point to the service disconnecting means. (CMP-4)

The term service conductors is broad and may include overhead service conductors, underground service conductors, and service-entrance conductors. This term specifically excludes any wiring on the supply side (serving utility side) of the service point. The service conductors originate at the service point (where the serving utility ends) and end at the service disconnect. These service conductors may originate only from the serving utility. The definition no longer includes service drops and service laterals; these terms now only apply to conductors that are under the control of the serving utility.

If the utility has specified that the service point is at the utility pole, the service conductors from an overhead distribution system originate at the utility pole and terminate at the service disconnecting means.

If the utility has specified that the service point is at the utility manhole, the service conductors from an underground distribution system originate at the utility manhole and terminate at the service disconnecting means. Where utility-owned primary conductors are extended to outdoor pad-mounted transformers on private property, the service conductors originate at the secondary connections of the transformers only if the utility has specified that the service point is at the secondary connections.

Service Conductors, Overhead

The overhead conductors between the service point and the first point of connection to the service-entrance conductors at the building or other structure. (CMP-4)

Service Conductors, Underground

The underground conductors between the service point and the first point of connection to the service-entrance conductors in a terminal box, meter, or other enclosure, inside or outside the building wall. (CMP-4)

Informational Note: Where there is no terminal box, meter, or other enclosure, the point of connection is considered to be the point of entrance of the service conductors into the building.

Service Drop

The overhead conductors between the utility electric supply system and the service point. (CMP

This definition correlates with the definition of the term service lateral. Service-drop and service lateral conductors are conductors on the line side of the service point and are not subject to the NEC. Overhead conductors on the load side of the service point are overhead service conductors.

The utility specifies the location of the service point. Exact locations of the service point can vary from utility to utility as well as from occupancy to occupancy.

Service-Entrance Conductors, Overhead System

The service conductors between the terminals of the service equipment and a point usually outside the building, clear of building walls, where joined by tap or splice to the service drop or overhead service conductors. (CMP-4)

Service-Entrance Conductors, Underground System

The service conductors between the terminals of the service equipment and the point of connection to the service lateral or underground service conductors. (CMP-4)

Informational Note: Where service equipment is located outside the building walls, there may be no service-entrance conductors or they may be entirely outside the building.

Service Equipment

The necessary equipment, usually consisting of a circuit breaker(s) or switch(es) and fuse(s) and their accessories, connected to the load end of service conductors to a building or other structure, or an otherwise designated area, and intended to constitute the main control and cutoff of the supply. (CMP-4)

Service equipment may consist of circuit breakers or fused switches that are provided to disconnect all ungrounded conductors in a building or other structure from the service-entrance conductors. Individual meter socket enclosures are not considered service equipment according to 230.66.

The disconnecting means at any one location in a building or other structure is not allowed to consist of more than six circuit breakers or six switches. The disconnecting means is required to be readily accessible either outside or inside nearest the point of entrance of the service-entrance conductors.

Service Lateral

The underground conductors between the utility electric supply system and the service point. (CMP-4)

Service-drop and service-lateral conductors are conductors on the line side of the service point and are not subject to the requirements of the NEC. In other words, these conductors are under the exclusive control of the utility. Underground conductors on the load side of the service point are underground service conductors.

Service Point

The point of connection between the facilities of the serving utility and the premises wiring. (CMP-4)

Informational Note: The service point can be described as the point of demarcation between where the serving utility ends and the premises wiring begins. The serving utility generally specifies the location of the service point based on the conditions of service.

The exact location for a service point is generally determined by the utility and may vary from utility to utility. Only those conductors that are located on the premises wiring side of the service point are covered by the NEC.

Conductors on the serving utility side of the service point generally are not covered by the NEC. For example, a typical suburban residence has overhead conductors from the utility pole to the house. If the utility specifies that the service point is at the point of attachment of the overhead conductors to the house, the overhead conductors are service-drop conductors that are not covered by the NEC because the conductors are not on the premises wiring side of the service point. Alternatively, if the utility specifies that the service point is at the pole, the overhead conductors are considered overhead service conductors, and the NEC would apply to these conductors.

Short-Circuit Current Rating

The prospective symmetrical fault current at a nominal voltage to which an apparatus or system is able to be connected without sustaining damage exceeding defined acceptance criteria. (CMP-10)

Show Window

Any window, including windows above doors, used or designed to be used for the display of goods or advertising material, whether it is fully or partly enclosed or entirely open at the rear and whether or not it has a platform raised higher than the street floor level. (CMP-2)

Signaling Circuit

Any electrical circuit that energizes signaling equipment. (CMP-3)

Simple Apparatus [as applied to Hazardous (Classified) Locations]

An electrical component or combination of components of simple construction with well-defined electrical parameters that does not generate more than 1.5 volts, 100 mA, and 25 mW, or a passive component that does not dissipate more than 1.3 watts and is compatible with the intrinsic safety of the circuit in which it is used. (CMP-14)

• Informational Note: The following apparatus are examples of simple apparatus:
• Passive components; for example, switches, junction boxes, resistance temperature devices, and simple semiconductor devices such as LEDs
• Sources of stored energy consisting of single components in simple circuits with well-defined parameters; for example, capacitors or inductors, whose values are considered when determining the overall safety of the system
• Sources of generated energy; for example, thermocouples and photocells, that do not generate more than 1.5 volts, 100 mA, and 25 mW

Special Permission

The written consent of the authority having jurisdiction. (CMP-1)

The AHJ for enforcement of the NEC is responsible for making interpretations and granting special permission contemplated in a number of the rules as stated in 90.4.

Stand-Alone System

A system that supplies power independently of an electrical production and distribution network.(CMP-4)

Structure

That which is built or constructed, other than equipment. (CMP-1)

Surge Arrester

A protective device for limiting surge voltages by discharging or bypassing surge current; it also prevents continued flow of follow current while remaining capable of repeating these functions. (CMP-5)

Surge-Protective Device (SPD)

A protective device for limiting transient voltages by diverting or limiting surge current; it also prevents continued flow of follow current while remaining capable of repeating these functions and is designated as follows:

Type 1: Permanently connected SPDs intended for installation between the secondary of the service transformer and the line side of the service disconnect overcurrent device.

Type 2: Permanently connected SPDs intended for installation on the load side of the service disconnect overcurrent device, including SPDs located at the branch panel.

Type 3: Point of utilization SPDs.

Type 4: Component SPDs, including discrete components, as well as assemblies. (CMP-5)

Informational Note: For further information on Type 1, Type 2, Type 3, and Type 4 SPDs, see UL 1449, Standard for Surge Protective Devices.

Switch, Bypass Isolation

A manually operated device used in conjunction with a transfer switch to provide a means of directly connecting load conductors to a power source and of disconnecting the transfer switch. (CMP-13)

Switch, General-Use

A switch intended for use in general distribution and branch circuits. It is rated in amperes, and it is capable of interrupting its rated current at its rated voltage. (CMP-9)

Switch, General-Use Snap

A form of general-use switch constructed so that it can be installed in device boxes or on box covers, or otherwise used in conjunction with wiring systems recognized by this Code. (CMP-9)

Switch, Isolating

A switch intended for isolating an electrical circuit from the source of power. It has no interrupting rating, and it is intended to be operated only after the circuit has been opened by some other means. (CMP-9)

Switch, Motor-Circuit

A switch rated in horsepower that is capable of interrupting the maximum operating overload current of a motor of the same horsepower rating as the switch at the rated voltage. (CMP-11)

Switch, Transfer

An automatic or nonautomatic device for transferring one or more load conductor connections from one power source to another. (CMP-13)

Switchboard

A large single panel, frame, or assembly of panels on which are mounted on the face, back, or both, switches, overcurrent and other protective devices, buses, and usually instruments. These assemblies are generally accessible from the rear as well as from the front and are not intended to be instal⁠led in cabinets. (CMP-9)

Modern switchboards are totally enclosed to minimize the probability of spreading fire to adjacent combustible materials and to guard live parts. Busbars are arranged to avoid inductive overheating of the enclosure or any nearby metal. Service busbars are isolated by barriers from the remainder of the switchboard to avoid inadvertent contact by personnel or tools during maintenance.

Switchgear

An assembly completely enclosed on all sides and top with sheet metal (except for ventilating openings and inspection windows) and containing primary power circuit switching, interrupting devices, or both, with buses and connections. The assembly may include control and auxiliary devices. Access to the interior of the enclosure is provided by doors, removable covers, or both. (CMP-9)

Informational Note: All switchgear subject to NEC requirements is metal enclosed. Switchgear rated below 1000 V or less may be identified as “low-voltage power circuit breaker switchgear.” Switchgear rated over 1000 V may be identified as “metal-enclosed switchgear” or “metal-clad switchgear.” Switchgear is available in non–arc-resistant or arc-resistant constructions.

Thermal Protector (as applied to motors)

A protective device for assembly as an integral part of a motor or motor-compressor that, when properly applied, protects the motor against dangerous overheating due to overload and failure to start. (CMP-11)

Informational Note: The thermal protector may consist of one or more sensing elements integral with the motor or motor-compressor and an external control device.

Thermally Protected (as applied to motors)

The words Thermally Protected appearing on the nameplate of a motor or motor-compressor indicate that the motor is provided with a thermal protector. (CMP-11)

Unclassified Locations [as applied to Hazardous (Classified) Locations]

Locations determined to be neither Class I, Division 1; Class I, Division 2; Class I, Zone 0; Class I, Zone 1; Class I, Zone 2; Class II, Division 1; Class II, Division 2; Class III, Division 1; Class III, Division 2; Zone 20; Zone 21; Zone 22; nor any combination thereof. (CMP-14)

Ungrounded

Not connected to ground or to a conductive body that extends the ground connection. (CMP-5)

Uninterruptible Power Supply

A power supply used to provide alternating current power to a load for some period of time in the event of a power failure. (CMP-13)

Informational Note: In addition, it may provide a more constant voltage and frequency supply to the load, reducing the effects of voltage and frequency variations.

Utilization Equipment

Equipment that utilizes electric energy for electronic, electromechanical, chemical, heating, lighting, or similar purposes. (CMP-1)

Ventilated

Provided with a means to permit circulation of air sufficient to remove an excess of heat, fumes, or vapors.(CMP-14).

Volatile Flammable Liquid

A flammable liquid having a flash point below 38°C (100°F), or a flammable liquid whose temperature is above its flash point, or a Class II combustible liquid that has a vapor pressure not exceeding 276 kPa (40 psia) at 38°C (100°F) and whose temperature is above its flash point. (CMP-14)

The flash point is defined as the minimum temperature of a liquid at which sufficient vapor is given off to form an ignitible mixture with the air, near the surface of the liquid or within the vessel used to contain the liquid. An ignitible mixture is defined as a mixture within the explosive or flammable range (between upper and lower limits) that is capable of the propagation of flame away from the source of ignition when ignited. Some emission of vapors takes place below the flash point but not enough to form an ignitible mixture.

Voltage (of a circuit)

The greatest root-mean-square (rms) (effective) difference of potential between any two conductors of the circuit concerned. (CMP-1)

Informational Note: Some systems, such as 3-phase 4-wire, single-phase 3-wire, and 3-wire direct current, may have various circuits of various voltages.

Common 3-phase, 4-wire wye systems are 480/277 volts and 208/120 volts. The voltage of the circuit is the higher voltage between any two phase conductors (i.e., 480 volts or 208 volts). The voltage of a single-phase, 2-wire feeder or branch-circuit (with a grounded conductor) derived from these systems would be the voltage between the two conductors (i.e., 277 volts or 120 volts). The same applies to direct current (dc) or single-phase, 3-wire systems where there are two voltages.

Voltage, Nominal

A nominal value assigned to a circuit or system for the purpose of conveniently designating its voltage class (e.g., 120/240 volts, 480Y/277 volts, 600 volts). (CMP-1)

• Informational Note No. 1: The actual voltage at which a circuit operates can vary from the nominal within a range that permits satisfactory operation of equipment.
• Informational Note No. 2: See ANSI C84.1-2011, Voltage Ratings for Electric Power Systems and Equipment (60 Hz).
• Informational Note No. 3: Certain battery units may be considered to be rated at nominal 48 volts dc, but may have a charging float voltage up to 58 volts. In dc applications, 60 volts is used to cover the entire range of float voltages.

Voltage to Ground

For grounded circuits, the voltage between the given conductor and that point or conductor of the circuit that is grounded; for ungrounded circuits, the greatest voltage between the given conductor and any other conductor of the circuit. (CMP-1)

Watertight

Constructed so that moisture will not enter the enclosure under specified test conditions. (CMP-1)

Weatherproof

Constructed or protected so that exposure to the weather will not interfere with successful operation. (CMP-1)

Informational Note: Rainproof, raintight, or watertight equipment can fulfill the requirements for weatherproof where varying weather conditions other than wetness, such as snow, ice, dust, or temperature extremes, are not a factor.