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1 General

368.17(C). The exceptions to 404.8(A) are illustrated as follows: in (c), busway switches installed according to Exception No. 1; in (d), a switch installed adjacent to a motor according to Exception No. 2; and in (e), a hookstick-operated isolating switch installed according to Exception No. 3.

A ccessible (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.

Wiring methods located behind removable panels designed to allow access are not considered permanently enclosed and are considered exposed (as applied to wiring methods). See 300.4(C) regarding cables located in spaces behind accessible panels. Exhibit 100.2 is an example of wiring methods and equipment that are considered accessible despite being located above a sus-pended ceiling.

Scope. This article contains only those definitions essential to the proper application of this Code. It is not intended to include commonly defined general terms or commonly defined technical terms from related codes and standards. In general, only those terms that are used in two or more articles are defined in Article 100. Other definitions are included in the article in which they are used but may be referenced in Article 100.

Part I of this article contains definitions intended to apply wherever the terms are used throughout this Code. Part II con-tains definitions applicable only to articles and parts of articles specifically covering installations and equipment operating at over 600 volts, nominal.

Commonly defined general terms include those terms defined in general English language dictionaries and terms that are not used in a unique or restricted manner in the NEC. Commonly defined technical terms such as volt (abbreviated V) and ampere (abbrevi-ated A) are found in the Authoritative Dictionary of IEEE Standards Terms.

Some definitions are not listed in Article 100 but are included in the Code article in which the term is used. For articles that fol-low the common format according to the NEC Style Manual, the section number is generally XXX.2 Definition(s). For example, the definition of nonmetallic-sheathed cable is found in 334.2.

I . GeneralA ccessible (as applied to equipment). Admitting close approach; not guarded by locked doors, elevation, or other effec-tive means.

Exhibit 100.1 illustrates equipment considered accessible (as applied to equipment) in accordance with requirements elsewhere in the Code. The requirement for the accessibility of switches and circuit breakers used as switches is shown in (a) and is according to 404.8(A). In (b), the busway installation is according to

ARTICLE 100Definitions

EXHIBIT 100.1 An example of a busway and of switches considered accessible even if located above the 6 feet 7 inch maximum height of the switch handle specified in 404.8(A).

6 ft 7 in.max.

ON

OFF

ON

OFF

(a) Manually operated disconnect switch

(b) Busway installation

(c) Installation of busway switches

Chain- or rope-operated switch

Hookstick- operated switch

(e) Hookstick-operated isolating switch

(d) Switchinstalled adjacentto motor

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Article 100 ● Definitions

National Electrical Code Handbook 2014 9

A ccessible, Readily (Readily Accessible). Capable of being reached quickly for operation, renewal, or inspections without requiring those to whom ready access is requisite to actions such as to use tools, to climb over or remove obstacles, or to resort to portable ladders, and so forth.

The definition of readily accessible does not preclude using locks on service equipment doors or doors of rooms containing service equipment, provided a key or lock combination is available to those for whom ready access is necessary. If a tool is necessary to gain access, the equipment is not readily accessible. Sections 230.70(A)(1) and 230.205(A) require service-disconnecting means to be readily accessible. However, 230.205(A) permits overhead or underground primary distribution systems on services of over 1000 volts, nominal on private property to have a disconnecting means that is not readily accessible, provided there is a readily accessible means to operate the disconnecting means through a mechanical linkage or through an electronically actuated method.

Section 225.32 requires that feeder disconnecting means for separate buildings be readily accessible. A commonly used, per-mitted practice is to locate the disconnecting means in the electri-cal equipment room of an office building or large apartment building and to keep the door to that room locked to prevent access by unauthorized persons. Section 240.24(A) requires that overcurrent devices be located so as to be readily accessible. Exhibit 100.3 shows an example of a locked electrical equipment door with a warning sign that restricts access.

A djustable Speed Drive. Power conversion equipment that provides a means of adjusting the speed of an electric motor.

The definitions for adjustable speed drives and adjustable speed drive systems were relocated from 430.2 for this edition.

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.

A djustable Speed Drive System. A combination of an adjust-able speed drive, its associated motor(s), and auxiliary equipment.

A mpacity. The maximum current, in amperes, that a conduc-tor can carry continuously under the conditions of use without exceeding its temperature rating.

Ambient temperature is a condition of use. A conductor with insu-lation rated at 60°C and installed near a furnace where the ambi-ent temperature is continuously maintained at 60°C has no current-carrying capacity. Any current flowing through the con-ductor will raise its temperature above the 60°C insulation rating. Therefore, the ampacity of this conductor, regardless of its size, is zero. See the ampacity correction factors for temperature in Tables 310.15(B)(2)(a) and 310.15(B)(2)(b), or see Informative Annex B. The temperature limitation of conductors is further explained and examples are given in the commentary following 310.15(B)(2). Another condition of use is the number of conductors in a raceway or cable, because the additional conductors raise the temperature in the raceway, decreasing the available ampac-ity. [See 310.15(B)(3)(a).]

A ppliance. Utilization equipment, generally other than indus-trial, 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.

A pproved. Acceptable to the authority having jurisdiction.

EXHIBIT 100.2 An example of an accessible busway and junction box located above hung ceilings with lift-out panels.

ON

OFF

Junctionbox

Busway

Suspended ceilingwith lift-out panels

Lay-in luminaire

EXHIBIT 100.3 A warning sign on a locked electrical equipment door.



10 2014 National Electrical Code Handbook

See the definition of authority having jurisdiction and 110.2 for a better understanding of the approval process. Typically, approval of listed equipment is more readily given by an AHJ where the authority accepts a laboratory’s listing mark. Other options may be available for the jurisdiction to approve equipment, including evaluation by the inspection authority or field evaluation by a qualified laboratory or individual. Where an evaluation is con-ducted on site, industry standards such as NFPA 79, Electrical Stan-dard for Industrial Machinery, if applicable, can be used. NFPA 790, Standard for Competency of Third Party Field Evaluation Bodies, can be used to qualify evaluation services. NFPA 791, Recommended Prac-tice and Procedures for Unlabeled Electrical Equipment Evaluation, can be used to evaluate unlabeled equipment in accordance with nationally recognized standards and any requirements of the AHJ.

A rc-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.

Arc-fault circuit interrupters are evaluated in accordance with UL 1699, Standard for Arc-Fault Circuit-Interrupters, using testing methods that create or simulate arcing conditions to determine a product’s ability to detect and interrupt arcing faults. These devices are also tested to verify that arc detection is not inhibited by the presence of loads and circuit characteristics that mask the hazard-ous arcing condition. In addition, these devices are evaluated to determine resistance to unwanted tripping due to the presence of arcing that occurs in equipment under normal operating condi-tions or to a loading condition that closely mimics an arcing fault, such as a solid-state electronic ballast or a dimmed load.

A skarel. A generic term for a group of nonflammable synthetic chlorinated hydrocarbons used as electrical insulating media.

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.

A ttachment Plug (Plug Cap) (Plug). A device that, by insertion in a receptacle, establishes a connection between the conduc-tors of the attached flexible cord and the conductors connected permanently to the receptacle.

See 406.7 for requirements pertaining to attachment plugs and the configuration charts from NEMA WD 6, Wiring Devices — Dimensional Requirements, for general-purpose nonlocking and specific -purpose locking plugs and receptacles shown in Exhibit 406.3.

A uthority Having Jurisdiction (AHJ). An organization, office, or individual responsible for enforcing the requirements of a code or standard, or for approving equipment, materials, an installa-tion, or a procedure.

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 depart-ment, 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 installa-tions, the commanding officer or departmental official may be the authority having jurisdiction.

In the North American safety system, the importance of the role of the AHJ cannot be overstated. The AHJ verifies that an installa-tion complies with the Code. See also the definition of approved, 90.7, and 110.2.

A utomatic. Performing a function without the necessity of human intervention.

B athroom. 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.

B attery System. Interconnected battery subsystems consist-ing of one or more storage batteries and battery chargers, and can include inverters, converters, and associated electrical equipment.

This definition is suitable for use with all types of storage batter-ies. The system consists of all of the major components that are necessary to supply the desired output. A battery system can con-tain multiple batteries. Other equipment can include chargers, inverters, converters, and overcurrent protective devices.

B onded (Bonding). Connected to establish electrical continuity and conductivity.

B onding Conductor or Jumper. A reliable conductor to ensure the required electrical conductivity between metal parts required to be electrically connected.

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 conduc-tor 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 ground-ing path. Bonding jumpers may be found at service equipment [250.92(B)], equipment operating over 250 volts (250.97), and expansion fittings in metal raceways (250.98). Exhibit 100.4 shows the difference between concentric- and eccentric-type knockouts and illustrates one method of applying bonding jump-ers at these types of knockouts.




B onding Jumper, Equipment. The connection between two or more portions of the equipment grounding conductor.

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 enter-ing an open-bottom switchboard are usually not mechanically connected to the switchboard. Bonding jumpers provide electri-cal continuity. An example of potential loss of both mechanical and electrical continuity would be an installation of an expan-sion fitting intended to allow for movement in a metal conduit system as illustrated in Exhibit 100.5. Expansion fittings consist of loosely joined raceways that allow expansion without deforma-tion of the raceway. Some expansion fittings for metal conduit have an internal bonding jumper that is integral to the fitting, eliminating the need for the external bonding jumpers shown in Exhibit 100.5. Equipment bonding jumpers are also used to con-nect the grounding terminal of a receptacle to a metal box that in turn is grounded via an equipment grounding conductor (the raceway system).

B onding Jumper, Main. The connection between the grounded circuit conductor and the equipment grounding conductor at the service.

Exhibit 100.6 shows a main bonding jumper that provides the connection between the grounded service conductor and the equipment grounding conductor at the service. Bonding jumpers may be located throughout the electrical system, but a main bonding jumper is located only at the service. Main bonding jumper requirements are found in 250.28.

B onding Jumper, System. The connection between the grounded circuit conductor and the supply-side bonding jumper, or the equipment grounding conductor, or both, at a separately derived system.

The system bonding jumper can be installed in several ways. For example, if a multi-barrel lug is connected to the XO terminal of a transformer, the system bonding jumper, grounding electrode conductor, grounded conductor, and bonding jumper can be con-nected at that connector. If a multi-barrel lug is connected to the transformer or generator enclosure, a common practice is to con-nect the system bonding jumper, the grounding electrode con-ductor, and the bonding jumper or conductor to that connector. The grounded conductor should always connect directly to the XO terminal. A system bonding jumper is used to connect the equipment grounding conductor(s) or the supply-side bonding jumper to the grounded conductor of a separately derived system

Bondingjumpers

Concentricknockout

Eccentricknockout

EXHIBIT 100.4 Bonding jumpers installed around concentric or eccentric knockouts.

EXHIBIT 100.5 Equipment bonding jumpers installed to maintain electrical continuity around conduit expansion fittings. (Courtesy of the International Association of Electrical Inspectors)

EXHIBIT 100.6 A main bonding jumper installed at the service between the grounded service conductor and the equipment grounding conductor.

Grounding electrode

Grounding electrodeconductor

Neutral bus

Equipment grounding bus

Main bonding jumper (maybe wire, bus, or screw)

Ungrounded serviceconductors

Grounded service conductor

Supply side equipmentbonding jumper




either at the source (see Exhibit 250.13) or at the first system dis-connecting means (see Exhibit 250.14). A system bonding jumper is used at the derived system if the derived system contains a grounded conductor.

Like the main bonding jumper at the service equipment, the system bonding jumper provides the necessary link between the equipment grounding conductors and the system grounded con-ductor in order to establish an effective path for ground-fault cur-rent to return to the source. The requirements for system bonding jumper(s) are found in 250.30(A)(1).

B ranch Circuit. The circuit conductors between the final over-current device protecting the circuit and the outlet(s).

Exhibit 100.7 shows the difference between branch circuits and feeders. Conductors between the overcurrent devices in the pan-elboards and the duplex receptacles are branch-circuit conduc-tors. Conductors between the service equipment or source of separately derived systems and the panelboards are feeders.

B ranch Circuit, Appliance. A branch circuit that supplies energy to one or more outlets to which appliances are to be con-nected and that has no permanently connected luminaires that are not a part of an appliance.

Two or more 20-ampere small-appliance branch circuits are required by 210.11(C)(1) for dwelling units. Section 210.52(B)(1) requires that these circuits supply receptacle outlets located in rooms such as the kitchen and pantry. These small-appliance branch circuits are not permitted to supply other outlets or perma-nently connected luminaires. (See 210.52 for details.)

B ranch Circuit, General-Purpose. A branch circuit that supplies two or more receptacles or outlets for lighting and appliances.

B ranch Circuit, Individual. A branch circuit that supplies only one utilization equipment.

Exhibit 100.8 illustrates an individual branch circuit with a single receptacle for connection of one piece of utilization equipment (e.g., one dryer, one range, one space heater, one motor). See 210.23 for permissible loads on individual branch circuits and see 210.21(B)(1), which requires the single receptacle to have an ampere rating not less than that of the branch circuit. A branch circuit supplying one duplex receptacle that supplies two cord-and-plug-connected appliances or similar equipment is not an individual branch circuit.

B ranch 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 volt-age between it and each ungrounded conductor of the circuit and that is connected to the neutral or grounded conductor of the system.

See 210.4, 240.15(B)(1), and 300.13(B) for specific information about multiwire branch circuits.

B uilding. A structure that stands alone or that is cut off from adjoining structures by fire walls with all openings therein pro-tected by approved fire doors.

A building is generally considered to be a roofed or walled struc-ture that is intended for supporting or sheltering any use or occu-pancy. However, a separate structure such as a pole, billboard sign, or water tower may also 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 sepa-rates buildings or subdivides a building to prevent the spread of fire and that has a fire resistance rating and structural stability. Fire doors (and fire windows) are used to protect openings in

EXHIBIT 100.7 Feeder (circuits) and branch circuits.

Branch Circuits

Panelboard

Panelboard

Feeder

Feeder

Serviceequipment

Generator

EXHIBIT 100.8 An individual branch circuit, supplying only one piece of utilization equipment via a single receptacle.

Single receptacle

Panelboard

Individual branch circuit

Utilizationequipment




walls, floors, and ceilings against the spread of fire and smoke within, into, or out of buildings.

C abinet. An enclosure that is designed for either surface mount-ing or flush mounting and is provided with a frame, mat, or trim in which a swinging door or doors are or can be hung.

Both cabinets and cutout boxes are covered in Article 312. Cabinets are designed for surface or flush mounting with a trim to which a swinging door(s) is hung. Cutout boxes are designed for surface mounting with a swinging door(s) secured directly to the box. Panel-boards are electrical assemblies designed to be placed in a cabinet or cutout box. (See the definitions of cutout box and panelboard.)

C able Routing Assembly. A single channel or connected mul-tiple 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 infor-mation technology and communications equipment, Class 2 and Class 3 cables, and power-limited fire alarm cables.

C harge Controller. Equipment that controls dc voltage or dc current, or both, and that is used to charge a battery or other energy storage device.

C ircuit 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.

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

A djustable (as applied to circuit breakers). A qualifying term indicating that the circuit breaker can be set to trip at various values of current, time, or both, within a predetermined range.

I nstantaneous Trip (as applied to circuit breakers). A qualify-ing term indicating that no delay is purposely introduced in the tripping action of the circuit breaker.

I nverse Time (as applied to circuit breakers). A qualifying term indicating that there is purposely introduced a delay in the trip-ping action of the circuit breaker, which delay decreases as the magnitude of the current increases.

N onadjustable (as applied to circuit breakers). A qualifying term indicating that the circuit breaker does not have any adjust-ment to alter the value of the current at which it will trip or the time required for its operation.

S etting (of circuit breakers). The value of current, time, or both, at which an adjustable circuit breaker is set to trip.

C lothes Closet. A nonhabitable room or space intended primar-ily for storage of garments and apparel.

This definition helps to determine whether the rules of 240.24(D), 410.16, and 550.11(A) apply to an installation. If the definition

does not apply, the area may be classified as something other than a clothes closet, such as a bedroom. Other requirements may then be applied, such as 210.52 and 210.70.

C ommunications 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 equip-ment (e.g., computers), and conductors dedicated solely to the operation of the equipment.

This definition indicates that communications equipment includes related power supplies and computers. These related items are subject to the same requirements that apply to communications equipment. This definition correlates with NFPA 76, Standard for the Fire Protection of Telecommunications Facilities.

Communications Raceway. An enclosed channel of nonme-tallic materials designed expressly for holding communications wires and cables, typically communications wires and cables and optical fiber and data (Class 2 and Class 3) in plenum, riser, and general-purpose applications.

C oncealed. Rendered inaccessible by the structure or finish of the building.

Raceways and cables supported or located within hollow frames or permanently closed in by the finish of buildings are considered concealed. Open-type work — such as 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 — is not considered concealed. [See definition of exposed (as applied to wiring methods).]

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

C onductor, Bare. A conductor having no covering or electrical insulation whatsoever.

C onductor, Covered. A conductor encased within material of composition or thickness that is not recognized by this Code as electrical insulation.

The green-covered equipment grounding conductors contained within a nonmetallic -sheathed cable and the uninsulated grounded system conductors within the overall exterior jacket of a Type SE cable are examples of covered conductors. Covered conductors should always be treated as bare conductors for working clearances because the covering does not have an insu-lation rating, so the conductors are effectively uninsulated. See the definition of insulated conductor that follows and the require-ments in Article 310.

C onductor, Insulated. A conductor encased within material of composition and thickness that is recognized by this Code as electrical insulation.




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) dielec-tric 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 should be consid-ered a covered conductor. See 310.104 for the requirements of insulated conductor construction and applications.

C onduit 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.

Conduit bodies include the short-radius type as well as capped elbows and service-entrance elbows. Some conduit bodies are referred to in the trade as “condulets” and include the LB, LL, LR, C, T, and X designs. A typical conduit body is shown in Exhibit 100.9. See 300.15 and Article 314 for rules on the usage of conduit bodies. Type FS and Type FD boxes, which are not classi-fied as conduit bodies, are listed with boxes in Table 314.16(A).

C onnector, 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.

C ontinuous Load. A load where the maximum current is expected to continue for 3 hours or more.

C ontrol 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.

C ontroller. 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.

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 and, in the case of motors, is required by 110.9 and 430.82 to be capable of inter-rupting the stalled rotor current of the motor. Stop-and-start sta-tions and similar control circuit components that do not open the power conductors to the motor are not considered controllers.

C ooking 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 mount-able controls.

C oordination (Selective). Localization of an overcurrent con-dition 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 avail-able fault current, and for the full range of overcurrent protective device opening times associated with those overcurrents.

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 over-loaded 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.

Selective coordination requirements include emergency sys-tems, legally required standby systems, and critical operations power systems in 700.28, 701.27, and 708.54, respectively.

EXHIBIT 100.9 Typical conduit bodies. (Courtesy of the National Electrical Contractors Association)




Requirements for selective coordination for elevator feeders are in 620.62. In 517.30(G), coordination is required only for faults that exceed 0.1 second in duration.

C opper-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.

C utout Box. An enclosure designed for surface mounting that has swinging doors or covers secured directly to and telescoping with the walls of the box proper.

D ead Front. Without live parts exposed to a person on the oper-ating side of the equipment.

D emand 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.

D evice. A unit of an electrical system, other than a conductor, that carries or controls electric energy as its principal function.

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

D isconnecting 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.

See also references for disconnecting means in the index.

D usttight. Constructed so that dust will not enter the enclosing case under specified test conditions.

Requirements for enclosures are found in 110.28, and Table 110.28, Enclosure Selection, provides a basis for selecting enclosure types that are dusttight. (See also the commentary fol-lowing the definition of enclosure.) Some dusttight constructions are only for wind-blown dust and may not be designed for com-bustible dusts found in Class II hazardous locations. The basic standard used to investigate dusttight enclosures for Class II, Divi-sion 2 locations is UL 1604, Electrical Equipment for Use in Class I and II, Division 2 and Class III Hazardous (Classified) Locations.

D uty, Continuous. Operation at a substantially constant load for an indefinitely long time.

D uty, Intermittent. Operation for alternate intervals of (1) load and no load; or (2) load and rest; or (3) load, no load, and rest.

D uty, Periodic. Intermittent operation in which the load condi-tions are regularly recurrent.

D uty, Short-Time. Operation at a substantially constant load for a short and definite, specified time.

D uty, Varying. Operation at loads, and for intervals of time, both of which may be subject to wide variation.

D welling, One-Family. A building that consists solely of one dwelling unit.

D welling, Two-Family. A building that consists solely of two dwelling units.

D welling, Multifamily. A building that contains three or more dwelling units.

D welling Unit. A single unit, providing complete and inde-pendent living facilities for one or more persons, including per-manent provisions for living, sleeping, cooking, and sanitation.

Where dwelling units are referenced throughout the Code, it is important to note that some rooms in motels, hotels, and similar occupancies can be classified as dwelling units if they satisfy the requirements of the definition. Exhibit 100.10 illustrates a motel or hotel room that clearly meets the definition because it has perma-nent provisions for living, sleeping, cooking, and sanitation. See also the definition of mobile home in 550.2.

E ffective Ground-Fault Current Path. An intentionally con-structed, 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.

E lectric 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.

EXHIBIT 100.10 An example of a motel or hotel room considered to be a dwelling unit.

Living

Sleeping

Eating

Clo

set

Coo

kingBath area

Ref

.




E lectric Sign. A fixed, stationary, or portable self-contained, electrically illuminated utilization equipment with words or sym-bols designed to convey information or attract attention.

E lectric-Discharge Lighting. Systems of illumination utiliz-ing fluorescent lamps, high-intensity discharge (HID) lamps, or neon tubing.

E lectronically Actuated Fuse. An overcurrent protective device that generally consists of a control module that provides current-sensing, electronically derived time–current characteris-tics, 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.

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

E nclosure. The case or housing of apparatus, or the fence or walls surrounding an installation to prevent personnel from acci-dentally contacting energized parts or to protect the equipment from physical damage.

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

Enclosures are required by 110.28 to be marked with a number that identifies the environmental conditions in which that type of enclosure can be used. Enclosures that comply with the require-ments for more than one type of enclosure are marked with mul-tiple designations. See the commentary following 110.28 for details on enclosure markings and types as well as Table 110.28, which lists the types of enclosures required to be used in specific locations.

E nergized. Electrically connected to, or is, a source of voltage.

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. Also see the definitions of exposed (as applied to live parts) and live parts.

E quipment. A general term, including fittings, devices, appli-ances, luminaires, apparatus, machinery, and the like used as a part of, or in connection with, an electrical installation.

This definition clarifies that machinery is considered equipment. For further information on machinery, see Article 670 and NFPA 79, Electrical Standard for Industrial Machinery.

E xplosionproof 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.

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

E xposed (as applied to live parts). Capable of being inadver-tently touched or approached nearer than a safe distance by a person.

The installation instructions should be consulted to ensure that live parts are properly guarded. See 110.27 for the requirements for guarding live parts. Also see the definitions of energized and live parts.

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

E xposed (as applied to wiring methods). On or attached to the surface or behind panels designed to allow access.

See Exhibit 100.2, which illustrates wiring methods that would be considered exposed because they are located above a suspended ceiling with lift-out panels.

E xternally Operable. Capable of being operated without expos-ing the operator to contact with live parts.

F eeder. 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.

See the commentary following the definition of branch circuit, including Exhibit 100.7, which illustrates the difference between branch circuits and feeders.

F estoon Lighting. A string of outdoor lights that is suspended between two points.

F itting. An accessory such as a locknut, bushing, or other part of a wiring system that is intended primarily to perform a mechani-cal rather than an electrical function.

Condulets, conduit couplings, EMT connectors and couplings, and threadless connectors are considered fittings.

G arage. 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.

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

G round. The earth.

G round Fault. An unintentional, electrically conductive connec-tion between an ungrounded conductor of an electrical circuit and the normally non–current-carrying conductors, metallic enclo-sures, metallic raceways, metallic equipment, or earth.

G rounded (Grounding). Connected (connecting) to ground or to a conductive body that extends the ground connection.

G rounded, Solidly. Connected to ground without inserting any resistor or impedance device.




G rounded Conductor. A system or circuit conductor that is intentionally grounded.

G round-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.

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.

The commentary following 210.8 contains a list of applicable cross-references for GFCIs. See Exhibits 210.6 through 210.8 for further information on GFCIs.

G round-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.

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 duct-ing; reinforcing steel; shields of communications cables; and the earth itself.

G round-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 pro-tection is provided at current levels less than those required to protect conductors from damage through the operation of a sup-ply circuit overcurrent device.

See the commentary following 230.95, 426.28, and 427.22.

G rounding 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 elec-trode conductor, or both.

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.

G rounding Electrode. A conducting object through which a direct connection to earth is established.

G rounding 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.

Grounding electrode conductors are covered extensively in Article 250, Part III. These conductors are required by 250.62 to be cop-per, aluminum, or copper-clad aluminum and are required to be

sized according to 250.66 and Table 250.66. Exhibit 100.6 and Exhibit 250.1 show a grounding electrode conductor in a typical grounding system for a single-phase, 3-wire service.

G uarded. 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.

G uest Room. An accommodation combining living, sleeping, sanitary, and storage facilities within a compartment.

G uest 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.

Some requirements for guest rooms in hotels, motels, and similar occupancies are found in 210.60. If a guest room or guest suite meets the definition of a dwelling unit, additional dwelling unit requirements may apply.

H andhole Enclosure. An enclosure for use in underground sys-tems, 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.

Exhibit 100.11 shows the installation of one type of handhole enclosure. Handhole enclosures are required by 314.30 to be “identified” for use in underground systems.

H ermetic 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.

EXHIBIT 100.11 An example of a handhole enclosure. (Courtesy of Quazite/Hubbell Lenoir City, Inc.)




H oistway. Any shaftway, hatchway, well hole, or other vertical opening or space in which an elevator or dumbwaiter is designed to operate.

H ybrid 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 defini-tion. The energy regenerated by an overhauling (descending) elevator does not constitute a power source for the purpose of this definition.

I dentified (as applied to equipment). Recognizable as suit-able for the specific purpose, function, use, environment, application, and so forth, where described in a particular Code requirement.

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

I n 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.

Several requirements are in the Code for a disconnecting means to be in sight from the equipment that it controls. For example, 430.102 requires the disconnecting means to be in sight from the controller. Of the three exceptions, two permit the disconnect to be located elsewhere. Both of these exceptions require that the disconnect be capable of being locked open. Exhibit 430.18 depicts requirements for the placement of a disconnecting means that is not in sight of a motor.

I ndustrial Control Panel. An assembly of two or more com-ponents 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 cir-cuit 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.

I nteractive System. An electric power production system that is operating in parallel with and capable of delivering energy to an electric primary source supply system.

I nterrupting Rating. The highest current at rated voltage that a device is identified to interrupt under standard test conditions.

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. Sections specifically dealing with interrupting ratings are 110.9, 240.60(C), 240.83(C), and 240.86. Exhibit 100.12 depicts the label of a 1600-ampere frame circuit breaker, showing the interrupting capacity ratings. See also the definition of short-circuit current rating.

I ntersystem Bonding Termination. A device that provides a means for connecting intersystem bonding conductors for com-munications systems to the grounding electrode system.

An intersystem bonding termination is a dedicated location for terminating the equipment grounding conductors required in Chapter 8 and 770.93 to the service, building, or structure’s grounding electrode system. This important safety measure pre-vents voltage differences between the equipment grounding con-ductors of the communication system and the power system. Frequently in new construction, the grounding electrode, the race-way, and the grounding electrode conductor are hidden behind walls and are not accessible for bonding connection.

I solated (as applied to location). Not readily accessible to persons unless special means for access are used.

K itchen. An area with a sink and permanent provisions for food preparation and cooking.

L abeled. 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

EXHIBIT 100.12 Interrupting ratings information on the label of a 1600-ampere frame circuit breaker.




production of labeled equipment or materials, and by whose labeling the manufacturer indicates compliance with appropriate standards or performance in a specified manner.

Equipment and conductors required or permitted by this Code are acceptable only if they have been approved for a specific environ-ment or application by the AHJ as stated in 110.2. See 90.7 regard-ing the examination of equipment for safety. Listing or labeling by a qualified testing laboratory provides a basis for approval.

L ighting Outlet. An outlet intended for the direct connection of a lampholder or luminaire.

L ighting 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.

L isted. 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.

Informational Note: The means for identifying listed equipment may vary for each organization concerned with product evalua-tion, 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.

See also the definitions of approved, authority having jurisdiction (AHJ), identified (as applied to equipment), and labeled, which all have distinctly different meanings.

L ive Parts. Energized conductive components.

The definition of live parts is associated with all voltage levels, not just voltage levels that present a shock hazard. See the definitions of energized and exposed.

L ocation, Damp. Locations protected from weather and not subject to saturation with water or other liquids but subject to moderate degrees of moisture.

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

L ocation, Dry. A location not normally subject to dampness or wetness. A location classified as dry may be temporarily sub-ject to dampness or wetness, as in the case of a building under construction.

L ocation, 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.

The inside of a raceway in a wet location and a raceway installed underground are considered wet locations. Therefore, any con-ductors contained therein would be required to be suitable for wet locations.

A general requirement for protection against corrosion and deterioration is found in 300.6(D), which also identifies numerous examples of wet locations. The requirements for luminaires installed in wet locations are found in 410.10(A). See also patient care area in 517.2 for a definition of wet procedure locations in a patient care area. Suitable enclosures for wet locations can be found in Table 110.28.

L uminaire. 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.

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

Luminaire is the term specified by IESNA, the ANSI/UL safety standards, and the ANSI/NEMA performance standards for light-ing products previously referred to as “light fixtures” in the United States. Luminaire is also the term used in IEC standards and accepted globally.

M otor Control Center. An assembly of one or more enclosed sections having a common power bus and principally containing motor control units.

M ultioutlet Assembly. A type of surface, flush, or freestanding raceway designed to hold conductors and receptacles, assembled in the field or at the factory.

The definition of multioutlet assembly includes a reference to a freestanding assembly with multiple outlets, commonly called a power pole. In dry locations, metallic and nonmetallic multioutlet assemblies are permitted; however, they are not permitted to be installed if concealed. See Article 380 for details on recessing mul-tioutlet assemblies. Exhibit 100.13 shows a multioutlet assembly used for countertop appliances. Portable assemblies, often called “power strips” or “plug strips,” are not multioutlet assemblies but are “relocatable power taps.”

N eutral Conductor. The conductor connected to the neutral point of a system that is intended to carry current under normal conditions.

It is important to remember that the neutral conductor is a current-carrying conductor and is not safe to work on while energized.

N eutral 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.

Informational Note: At the neutral point of the system, the vecto-rial 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.

Exhibit 100.14 illustrates four examples of a neutral point in a system.

N onautomatic. Requiring human intervention to perform a function.

N onlinear Load. A load where the wave shape of the steady-state current does not follow the wave shape of the applied voltage.

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 in mod-ern circuits. Additional conductor heating is just one of the unde-sirable operational effects often associated with harmonic currents. Informational Note No. 1 following 310.15(A)(3) addresses that harmonic current, as well as fundamental current, should be used in 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 instru-ments. Averaging ammeters produces inaccurate values if used to measure nonlinear loads. See the commentary following 310.15(B)(5)(c).

O utlet. A point on the wiring system at which current is taken to supply utilization equipment.

This term 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.

O utline 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.

Outline lighting includes low-voltage, light-emitting diodes as well as other luminaires installed to form various shapes. See Article 600 for requirements for outline lighting.

O vercurrent. 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.

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

O vercurrent 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.

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

O vercurrent Protective Device, Supplementary. A device intended to provide limited overcurrent protection for specific applications and utilization equipment such as luminaires and

EXHIBIT 100.13 A multioutlet assembly installed to serve countertop appliances. (Courtesy of Legrand/Wiremold®)

Neutral conductor

Neutral point

Neutral conductor Neutral conductor

Wye Connections in aPolyphase System

Midpoint of a Single-Phase,3-Wire System

Neutral conductor

Single-Phase Portion of a 3-Phase

Delta System

Midpoint of a 3-Wire,Direct-Current System

Neutralpoint Neutral

point

Neutralpoint

EXHIBIT 100.14 Four examples of a neutral point.




appliances. This limited protection is in addition to the protec-tion provided in the required branch circuit by the branch-circuit overcurrent protective device.

There are two levels of overcurrent protection within branch cir-cuits: branch-circuit overcurrent protection and supplementary overcurrent protection. The devices used to provide overcurrent protection are different, and the differences are found in the prod-uct standards UL 489, Molded-Case Circuit Breakers, Molded-Case Switches and Circuit-Breaker Enclosures, and UL 1077, Supplementary Protectors for Use in Electrical Equipment.

The NEC requires that all branch circuits use only branch-circuit-rated overcurrent protective devices to protect branch cir-cuits, but it permits supplementary overcurrent protective devices for limited use downstream of the branch-circuit-rated overcur-rent protective device.

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 supple-mentary device must be in addition to and be protected by the more robust branch-circuit overcurrent protective device.

O verload. 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.

P anelboard. 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 with-out 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.

P hotovoltaic (PV) System. The total components and sub-system that, in combination, convert solar energy into electric energy suitable for connection to a utilization load.

P lenum. A compartment or chamber to which one or more air ducts are connected and that forms part of the air distribution system.

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 meth-ods 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 con-junction 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. The air-handling space

under a computer room floor has specific requirements as given in Article 645.

P ower Outlet. An enclosed assembly that may include recep-tacles, 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.

P remises Wiring (System). Interior and exterior wiring, includ-ing 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.

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

For this edition, a new informational note was added to clarify what a premises wiring system is. 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.

Q ualified 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.

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

This definition points out that safety training that qualifies a worker is training in hazard recognition and avoidance. See 110.6 in NFPA 70E®, Standard for Electrical Safety in the Workplace®, for the training requirements for qualified and unqualified persons who may be exposed to electrical hazards.

R aceway. An enclosed channel of metallic or nonmetallic mate-rials designed expressly for holding wires, cables, or busbars, with additional functions as permitted in this Code.

Cable trays (see Article 392) are support systems for wiring meth-ods and are not considered to be raceways.

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

R ainproof. Constructed, protected, or treated so as to prevent rain from interfering with the successful operation of the appa-ratus under specified test conditions.




See the commentary following 110.28.

R aintight. Constructed or protected so that exposure to a beat-ing rain will not result in the entrance of water under specified test conditions.

Table 110.28 provides information on enclosure types that are considered to be raintight. Related requirements for raintight boxes and cabinets are found in 300.6(A)(2).

R eceptacle. A receptacle is a contact device installed at the outlet for the connection of an attachment plug. A single recep-tacle 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.

R eceptacle Outlet. An outlet where one or more receptacles are installed.

R emote-Control Circuit. Any electrical circuit that controls any other circuit through a relay or an equivalent device.

Retrofit Kit. A general term for a complete subassembly of parts and devices for field conversion of utilization equipment.

S ealable Equipment. Equipment enclosed in a case or cabi-net that is provided with a means of sealing or locking so that live parts cannot be made accessible without opening the enclosure.

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

S eparately 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.

Examples of separately derived systems include generators, bat-teries, 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 connec-tion between systems. In addition, 250.30(A)(6) permits a com-mon grounding electrode conductor to be installed for multiple separately derived systems. This definition clarifies that those sys-tems 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. The grounded circuit con-ductors are not intended to be directly connected.

S ervice. The conductors and equipment for delivering elec-tric energy from the serving utility to the wiring system of the premises served.

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.

S ervice Cable. Service conductors made up in the form of a cable.

S ervice Conductors. The conductors from the service point to the service disconnecting means.

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 serv-ing utility ends) and end at the service disconnect. These service conductors may originate only from the serving utility. The defini-tion no longer includes service drops and service laterals, which are now conductors 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 sys-tem originate at the utility pole and terminate at the service dis-connecting means.

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

See Article 230, Part VIII, and the commentary following 230.200 for information on service conductors exceeding 1000 volts, nominal.

S ervice 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.

S ervice Conductors, Underground. The underground conduc-tors 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.

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.

S ervice Drop. The overhead conductors between the utility electric supply system and the service point.

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

In Exhibit 100.15, the service-drop conductors run from the utility pole and connect to the service-entrance conductors at the ser-vice point. Conductors on the utility side of the service point are not covered by the NEC. The utility specifies the location of the




service point. Exact locations of the service point may vary from utility to utility as well as from occupancy to occupancy.

S ervice-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.

See Exhibit 100.15 for an illustration of service-entrance conduc-tors in an overhead system. The system shows a service drop from a utility pole to attachment on a house and service-entrance conductors from point of attachment (spliced to service-drop con-ductors), down the side of the house, through the meter socket, and terminating in the service equipment. In this instance, the service point is at the drip loop. The conductors on the line side of the service point are under the control of the utility.

S ervice-Entrance Conductors, Underground System. The service conductors between the terminals of the service equip-ment and the point of connection to the service lateral or under-ground service conductors.

See Exhibit 100.16 for an illustration of service-entrance conductors in an underground system. The illustration on the top shows under-ground service lateral conductors run from a pole to a service point underground. The conductors from the service point into the build-ing are underground service conductors. The illustration on the bot-tom shows service lateral conductors run from a utility transformer.

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.

S ervice Equipment. The necessary equipment, usually con-sisting 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.

Service equipment may consist of circuit breakers or fused switches that are provided to disconnect all ungrounded conduc-tors in a building or other structure from the service-entrance con-ductors. 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 and is required to be readily accessible either outside or inside nearest the point of entrance of the service-entrance conductors. Requirements for service conductors outside the building are in 230.6, and those for disconnecting means are throughout Article 230, Part VI.

S ervice Lateral. The underground conductors between the util-ity electric supply system and the service point.

Service-drop conductors

Service-entranceconductors

Service point

EXHIBIT 100.15 Conductors in an overhead service.

EXHIBIT 100.16 Underground systems showing service laterals run from a pole (top) and from a transformer (bottom).

Service lateral

Service point

Service point

Service-entrance conductorsUnderground service conductor

Underground service conductorService lateral Terminal box Service-entrance conductors

Meter andserviceequipment

Meter andserviceequipment




This definition correlates with the definition of the term service-drop conductors. Service-drop and service lateral conductors are conductors on the line side of the service point and are not sub-ject to the requirements of the NEC. Underground conductors on the load side of the service point are underground service conductors.

As Exhibit 100.16 shows, the underground service laterals may be run from poles or from transformers and with or without terminal boxes, provided they terminate at the service point. The next transition would be to the underground service conductors, which would connect to the service-entrance conductors, or they may terminate in a terminal box, meter, or some other enclosure, which may be inside or outside of the building. Conductors on the utility side of the service point are not covered by the NEC. The utility specifies the location of the service point. Exact locations of the service point may vary from utility to utility as well as from occupancy to occupancy.

S ervice Point. The point of connection between the facilities of the serving utility and the premises wiring.

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 condi-tions of service.

The location of the service point is generally determined by the utility. Only those conductors that are located on the premises wiring side of the service point are covered by the NEC.

Any conductor on the serving utility side of the service point generally is not covered by the NEC. For example, a typical subur-ban 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 Code because the conductors are not on the prem-ises wiring side of the service point. Alternatively, if the utility specifies that the service point is at the pole, the overhead con-ductors are considered overhead service conductors, and the NEC would apply to these conductors.

Exact locations for a service point may vary from utility to utility as well as from occupancy to occupancy.

S hort-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.

The short-circuit current rating is marked on the equipment nameplate as shown in Exhibit 100.17. This value must not be exceeded. Otherwise, the equipment can be damaged by short-circuit currents, posing a hazard to personnel and property. See also the definition of interrupting rating.

S how Window. Any window 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.

S ignaling Circuit. Any electrical circuit that energizes signal-ing equipment.

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S pecial Permission. The written consent of the authority hav-ing jurisdiction.

The A HJ for enforcement of the Code is responsible for making inter-pretations and granting special permission contemplated in a num-ber of the rules as stated in 90.4. For requirements governing special permission situations, see 110.26(A)(1)(b), 230.2(B), and 426.14.

S tructure. That which is built or constructed.

S ubstation. An enclosed assemblage of equipment (e.g., switches, interrupting devices, circuit breakers, buses, and transformers) through which electric energy is passed for the purpose of distribu-tion, switching, or modifying its characteristics.

S urge Arrester. A protective device for limiting surge volt-ages by discharging or bypassing surge current; it also prevents continued flow of follow current while remaining capable of repeating these functions.

S urge-Protective Device (SPD). A protective device for limit-ing 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:

EXHIBIT 100.17 Short-circuit current rating on equipment nameplate.




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

Type 2: Permanently connected SPDs intended for installa-tion 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.

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

Type 1 and Type 2 surge-protective devices (SPDs) for perma-nently connected devices on circuits not exceeding 600 volts are included in UL 1449, Transient Voltage Surge Suppressors. Require-ments related to SPDs are found in Article 280.

S witch, 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 disconnect-ing the transfer switch.

S witch, 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.

S witch, General-Use Snap. A form of general-use switch con-structed 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.

S witch, 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.

S witch, Motor-Circuit. A switch rated in horsepower that is capable of interrupting the maximum operating overload cur-rent of a motor of the same horsepower rating as the switch at the rated voltage.

S witch, Transfer. An automatic or nonautomatic device for transferring one or more load conductor connections from one power source to another.

S witchboard. A large single panel, frame, or assembly of panels on which are mounted on the face, back, or both, switches, over-current and other protective devices, buses, and usually instru-ments. These assemblies are generally accessible from the rear as well as from the front and are not intended to be installed in cabinets.

Busbars are required to be arranged to avoid inductive overheat-ing. Service busbars are required to be isolated by barriers from the remainder of the switchboard. Although not required, most modern switchboards are totally enclosed to minimize the prob-

ability of spreading fire to adjacent combustible materials and to guard live parts.

S witchgear. An assembly completely enclosed on all sides and top with sheet metal (except for ventilating openings and inspec-tion 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.

This definition was revised for the 2014 Code. It formerly appeared as metal-enclosed power switchgear. The revised definition is inclu-sive of all types of switchgear governed by the NEC. The generic term can be used in most Code text where the term switchboard is already mentioned, and where the use of the term switchgear is appropriate. According to ANSI C37.20, Standard for Metal-Enclosed Low-Voltage Power Circuit Breaker Switchgear, the term switchgear includes “metal-enclosed low-voltage power circuit-breaker switchgear,” “metal-clad switchgear,” and “metal-enclosed inter-rupter switchgear.”

Informational Note: All switchgear subject to NEC require-ments 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.

T hermal 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.

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.

T hermally Protected (as applied to motors). The words Ther-mally Protected appearing on the nameplate of a motor or motor-compressor indicate that the motor is provided with a thermal protector.

U ngrounded. Not connected to ground or to a conductive body that extends the ground connection.

U ninterruptible Power Supply. A power supply used to pro-vide alternating current power to a load for some period of time in the event of a power failure.

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.

U tility-Interactive Inverter. An inverter intended for use in parallel with an electric utility to supply common loads that may deliver power to the utility.




U tilization Equipment. Equipment that utilizes electric energy for electronic, electromechanical, chemical, heating, lighting, or similar purposes.

V entilated. Provided with a means to permit circulation of air sufficient to remove an excess of heat, fumes, or vapors.

See the commentary following 110.13(B).

V olatile 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 combus-tible 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.

The flash point of a liquid is defined as the minimum temperature at which it gives off sufficient vapor 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.

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

Informational Note: Some systems, such as 3-phase 4-wire, single-phase 3-wire, and 3-wire direct current, may have vari-ous 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 the circuit of a 2-wire feeder or branch-circuit (sin-gle-phase and the grounded conductor) derived from these sys-tems would be the lower voltage between 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.

V oltage, 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).

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 C84.1-2006, Voltage Rat-ings for Electric Power Systems and Equipment (60 Hz).

For a list of nominal voltages to use in computing branch-circuit and feeder loads, see 220.5(A).

V oltage 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.

This definition can be best illustrated using examples.

System Voltage to Ground

480/277-volt wye 277208/120-volt wye 1203-phase, 3-wire ungrounded 480-volt 480

For a 3-phase, 4-wire delta system with the center of one leg grounded, there are three voltages to ground — that is, on a 240-volt system, two legs would each have 120 volts to ground, and the third, or high, leg would have 208 volts to ground. See 110.15, 230.56, and 408.3(E) for requirements pertaining to special mark-ings and arrangements on such circuit conductors.

W atertight. Constructed so that moisture will not enter the enclosure under specified test conditions.

Unless an enclosure is hermetically seal ed, it is possible for mois-ture to enter the enclosure. See the requirements related to water-tight enclosures in 110.28 and Table 110.28 and the additional information given in the accompanying commentary.

W eatherproof. Constructed or protected so that exposure to the weather will not interfere with successful operation.

Informational Note: Rainproof, raintight, or watertight equip-ment 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.

For information on enclosures considered to be weatherproof based on exposure to specific environmental conditions, see 110.28 and the accompanying commentary.

II. Over 600 Volts, NominalPart II contains definitions applicable only to the articles and parts of articles specifically covering installations and equipment operating at over 600 volts, nominal.

The definitions in Part I are intended to apply wherever the terms are used throughout this Code. The definitions in Part II are applicable only to articles and parts of articles specifically covering installations and equipment operating at over 600 volts, nominal.

E lectronically Actuated Fuse. An overcurrent protective device that generally consists of a control module that provides cur-rent sensing, electronically derived time–current characteristics, energy to initiate tripping, and an interrupting module that inter-rupts current when an overcurrent occurs. Electronically actu-ated fuses may or may not operate in a current-limiting fashion, depending on the type of control selected.

Although they are called fuses because they interrupt current by melting a fusible element, electronically actuated fuses respond to a signal from an electronic control, rather than from the heat generated by actual current passing through a fusible element. Electronically actuated fuses have controls similar to those of electronic circuit breakers.


Article 110 ● Requirements for Electrical Installations 110.3


F use. An overcurrent protective device with a circuit-opening fusible part that is heated and severed by the passage of overcur-rent through it.

Informational Note: A fuse comprises all the parts that form a unit capable of performing the prescribed functions. It may or may not be the complete device necessary to connect it into an electrical circuit.

C ontrolled Vented Power Fuse. A fuse with provision for con-trolling discharge circuit interruption such that no solid material may be exhausted into the surrounding atmosphere.

Informational Note: The fuse is designed so that discharged gases will not ignite or damage insulation in the path of the discharge or propagate a flashover to or between grounded members or con-duction members in the path of the discharge where the distance between the vent and such insulation or conduction members conforms to manufacturer’s recommendations.

E xpulsion Fuse Unit (Expulsion Fuse). A vented fuse unit in which the expulsion effect of gases produced by the arc and lining of the fuseholder, either alone or aided by a spring, extin-guishes the arc.

N onvented Power Fuse. A fuse without intentional provision for the escape of arc gases, liquids, or solid particles to the atmo-sphere during circuit interruption.

P ower Fuse Unit. A vented, nonvented, or controlled vented fuse unit in which the arc is extinguished by being drawn through solid material, granular material, or liquid, either alone or aided by a spring.

V ented Power Fuse. A fuse with provision for the escape of arc gases, liquids, or solid particles to the surrounding atmosphere during circuit interruption.

M ultiple Fuse. An assembly of two or more single-pole fuses.

S witching Device. A device designed to close, open, or both, one or more electrical circuits.

C ircuit Breaker. A switching device capable of making, carrying, and interrupting currents under normal circuit conditions, and also of making, carrying for a specified time, and interrupting currents under specified abnormal circuit conditions, such as those of short circuit.

C utout. An assembly of a fuse support with either a fuseholder, fuse carrier, or disconnecting blade. The fuseholder or fuse carrier may include a conducting element (fuse link) or may act as the disconnecting blade by the inclusion of a nonfusible member.

D isconnecting Means. A device, group of devices, or other means whereby the conductors of a circuit can be disconnected from their source of supply.

D isconnecting (or Isolating) Switch (Disconnector, Isolator). A mechanical switching device used for isolating a circuit or equip-ment from a source of power.

I nterrupter Switch. A switch capable of making, carrying, and interrupting specified currents.

O il Cutout (Oil-Filled Cutout). A cutout in which all or part of the fuse support and its fuse link or disconnecting blade is mounted in oil with complete immersion of the contacts and the fusible portion of the conducting element (fuse link) so that arc interruption by severing of the fuse link or by opening of the contacts will occur under oil.

O il Switch. A switch having contacts that operate under oil (or askarel or other suitable liquid).

R egulator Bypass Switch. A specific device or combination of devices designed to bypass a regulator.


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