DEFINITIONS

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 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 A of this article contains definitions intended to apply wherever the terms are used throughout this Code. Part B contains definitions applicable only to the parts of articles covering specifically installations and equipment operating at over 600 volts, nominal. A. General Accessible: (As applied to wiring methods.) Capable of being removed or exposed without damaging the building structure or finish, or not permanently closed in by the structure or finish of the building. (See "Concealed" and "Exposed.") Accessible: (As applied to equipment.) Admitting close approach: not guarded by locked doors, elevation, or other effective means. (See Accessible, Readily.") Accessible, Readily: (Readily Accessible.) Capable of being reached quickly for operation, renewal, or inspections, without requiring those to whom ready access is requisite to climb over or remove obstacles or to resort to portable ladders, chairs, etc. (See "Accessible.") Ampacity: The current in amperes that a conductor can carry continuously under the conditions of use without exceeding its temperature rating. Appliance: Utilization equipment, generally other than industrial, normally built in standardized sizes or types, that is installed or connected as a unit to perform one or more functions such as clothes washing, air conditioning, food mixing, deep frying, etc. Appliance Branch Circuit: See "Branch Circuit, Appliance." Approved: Acceptable to the authority having jurisdiction. Askarel: A generic term for a group of nonflammable synthetic chlorinated hydrocarbons used as electrical insulating media. 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 upon the askarel type. Attachment Plug (Plug Cap) (Cap): A device that, by insertion in a receptacle, establishes connection between the conductors of the attached flexible cord and the conductors connected permanently to the receptacle. 70-6 NATIONAL ELECTRICAL CODE Automatic: Self-acting, operating by its own mechanism when actuated by some impersonal influence, as for example, a change in current strength, pressure, temperature, or mechanical configuration. (See "Nonautomatic.") Bare Conductor: See under "Conductor." Bonding: The permanent joining of metallic parts to form an electrically conductive path that will assure electrical continuity and the capacity to conduct safely any current likely to be imposed. Bonding Jumper: A reliable conductor to assure the required electrical conductivity between metal parts required to be electrically connected. Bonding Jumper, Circuit: The connection between portions of a conductor in a circuit to maintain required ampacity of the circuit. Bonding Jumper, Equipment: The connection between two or more portions of the equipment grounding conductor. Bonding Jumper, Main: The connection between the grounded circuit conductor and the equipment grounding conductor at the service. Branch Circuit: The circuit conductors between the final overcurrent device protecting the circuit and the outlet(s). Branch Circuit, Appliance: A branch circuit supplying energy to one or more outlets to which appliances are to be connected; such circuits to have no permanently connected lighting fixtures not a part of an appliance. Branch Circuit, General Purpose: A branch circuit that supplies a number of outlets for lighting and appliances. Branch Circuit, Individual: A branch circuit that supplies only one utilization equipment. Branch Circuit, Multiwire: A branch circuit consisting of two or more ungrounded conductors having a potential difference between them, and a grounded conductor having equal potential difference between it and each ungrounded conductor of the circuit and that is connected to the neutral or grounded conductor of the system. Building: A structure that stands alone or that is cut off from adjoining doors. structures by fire walls with all openings therein protected by approved fire Cabinet: An enclosure designed either for surface or flush mounting and provided with a frame, mat, or trim in which a swinging door or doors are or may be hung. Circuit Breaker: A device designed to open and close a circuit by nonautomatic means and to open the circuit automatically on a predetermined overcurrent without damage to itself when properly applied within its rating. ARTICLE 100 - DEFINITIONS 70-7 (FPN): The automatic opening means can be integral, direct acting with the circuit breaker, or remote from the circuit breaker. Adjustable: (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. Instantaneous Trip: (As applied to circuit breakers.) A qualifying term indicating that no delay is purposely introduced in the tripping action of the circuit breaker. Inverse Time: (As applied to circuit breakers.) A qualifying term indicating that there is purposely introduced a delay in the tripping action of the circuit breaker, which delay decreases as the magnitude of the current increases. Nonadjustable: (As applied to circuit breakers.) A qualifying term indicating that the circuit breaker does not have any adjustment to alter the value of current at which it will trip or the time required for its operation. Setting: (of circuit breaker.) The value of current, time, or both at I which an adjustable circuit breaker is set to trip. Concealed: Rendered inaccessible by the structure or finish of the building. Wires in concealed raceways are considered concealed, even though they may become accessible by withdrawing them. [See "Accessible - (As applied to wiring methods)."] Conductor: Bare: A conductor having no covering or electrical insulation whatsoever. (See "Conductor, Covered.") Covered: A conductor encased within material of composition or thickness that is not recognized by this Code as electrical insulation. (See "Conductor, Bare.") Insulated: A conductor encased within material of composition and thickness that is recognized by this Code as electrical insulation. Conduit Body: A separate portion of a conduit or tubing system that provides access through a removable cover(s) to the interior of the system at a junction of two or more sections of the system or at a terminal point of the system. Boxes such as FS and FD or larger cast or sheet metal boxes are not classified as conduit bodies. Connector, Pressure (Solderless): A device that establishes a connection between two or more conductors or between one or more conductors and a terminal by means of mechanical pressure and without the use of solder. Continuous Duty: See under "Duty." Continuous Load: A load where the maximum current is expected to continue for three hours or more. 70-8 NATIONAL ELECTRICAL CODE Controller: A device or group of devices that serves to govern, in some predetermined manner, the electric power delivered to the apparatus to which it is connected. Cooking Unit, Counter-Mounted: A cooking appliance designed for mounting in or on a counter and consisting of one or more heating elements, internal wiring, and built-in or separately mountable controls. (See "Oven, Wall-Mounted.") Copper-Clad Aluminum Conductors: Conductors drawn from a copper-clad aluminum rod with the copper metallurgically bonded to an aluminum core. The copper forms a minimum of 10 percent of the crosssectional area of a solid conductor or each strand of a stranded conductor. Covered Conductor: See under "Conductor." Cutout Box: An enclosure designed for surface mounting and having swinging doors or covers secured directly to and telescoping with the walls of the box proper. (See "Cabinet.") Damp Location: See under "Location." Dead Front: Without live parts exposed to a person on the operating side of the equipment. Demand Factor: The ratio of the maximum demand of a system, or part of a system, to the total connected load of a system or the part of the system under consideration. Device: A unit of an electrical system that is intended to carry but not utilize electric energy. Disconnecting Means: A device, or group of devices, or other means by which the conductors of a circuit can be disconnected from their source of supply. Dry Location: See under "Location." Dustproof: So constructed or protected that dust will not interfere with its successful operation. Dusttight: So constructed that dust will not enter the enclosing case under specified test conditions. (FPN): For test conditions other than for rotating equipment, see Enclosures for Electrical Equipment (1000 Volts Maximum), Clause 6.5, ANSI/NEMA 250-1985. Duty: Continuous Duty: Operation at a substantially constant load for an indefinitely long time. Intermittent Duty: Operation for alternate intervals of (1) load and no load; or (2) load and rest; or (3) load, no load, and rest. Periodic Duty: Intermittent operation in which the load conditions are regularly recurrent. ARTICLE 100 - DEFINITIONS 70-9 Short-Time Duty: Operation at a substantially constant load for a short and definitely specified time. Varying Duty: Operation at loads, and for intervals of time, both of which may be subject to wide variation. Dwelling: Dwelling Unit: One or more rooms for the use of one or more persons as a housekeeping unit with space for eating, living, and sleeping, and permanent provisions for cooking and sanitation. Multifamily Dwelling: A building containing three or more dwelling units. One-Family Dwelling: A building consisting solely of one dwelling unit. Two-Family Dwelling: A building consisting solely of two dwelling units. Electric Sign: A fixed, stationary, or portable self-contained, electrically illuminated utilization equipment with words or symbols designed to convey information or attract attention. Enclosed: Surrounded by a case, housing, fence, or walls that will prevent persons from accidentally contacting energized parts. Enclosure: The case or housing of apparatus, or the fence or walls surrounding an installation to prevent personnel from accidentally contacting energized parts, or to protect the equipment from physical damage. (FPN): For enclosure types, see Enclosures for Electrical Equipment (1000 Volts Maximum), ANSI/NEMA 250-1985. Equipment: A general term including material, fittings, devices, appliances, fixtures, apparatus, and the like used as a part of, or in connection with, an electrical installation. Equipment Grounding Conductor: See "Grounding Conductor, Equipment." Explosionproof Apparatus: Apparatus 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. (FPN): For further information, see Explosion-Proof and Dust-Ignition-Proof Electrical Equipment for Use in Hazardous (Classified) Locations, ANSI/UL 1203- 1988. Exposed: (As applied to live parts.) Capable of being inadvertently touched or approached nearer than a safe distance by a person. It is applied to parts not suitably guarded, isolated, or insulated. (See "Accessible" and "Concealed.") 70-10 NATIONAL ELECTRICAL CODE Exposed: (As applied to wiring methods.) On or attached to the surface or behind panels designed to allow access. [See "Accessible - (As applied to wiring methods)."] Externally Operable: Capable of being operated without exposing the operator to contact with live parts. Feeder: All circuit conductors between the service equipment or the source of a separately derived system and the final branch-circuit overcurrent device. Fitting: An accessory such as a locknut, bushing, or other part of a wiring system that is intended primarily to perform a mechanical rather than an electrical function. Garage: A building or portion of a building in which one or more selfpropelled vehicles carrying volatile flammable liquid for fuel or power are kept for use, sale, storage, rental, repair, exhibition, or demonstrating purposes, and all that portion of a building that is on or below the floor or floors in which such vehicles are kept and that is not separated therefrom by suitable cutoffs. (FPN): For commercial garages, repair, and storage, see Section 511-1. General-Purpose Branch Circuit: See "Branch Circuit, General Purpose." General-Use Snap Switch: See under "Switches." General-Use Switch: See under "Switches." Ground: A conducting connection, whether intentional or accidental, between an electrical circuit or equipment and the earth, or to some conducting body that serves in place of the earth. Grounded: Connected to earth or to some conducting body that serves in place of the earth. Grounded, Effectively: Intentionally connected to earth through a ground connection or connections of sufficiently low impedance and having sufficient current-carrying capacity to prevent the buildup of voltages that may result in undue hazards to connected equipment or to persons. Grounded Conductor: A system or circuit conductor that is intentionally grounded. Grounding Conductor: A conductor used to connect equipment or the grounded circuit of a wiring system to a grounding electrode or electrodes. Grounding Conductor, Equipment: The conductor used to connect the noncurrent-carrying metal parts of equipment, raceways, and other enclosures to the system grounded conductor, the grounding electrode conductor, or both, at the service equipment or at the source of a separately derived system. ARTICLE 100 - DEFINITIONS 70-11 Grounding Electrode Conductor: The conductor used to connect the grounding electrode to the equipment grounding conductor, to the grounded conductor, or to both, of the circuit at the service equipment or at the source of a separately derived system. Ground-Fault Circuit-Interrupter: A device intended for the protection of personnel that functions to deenergize a circuit or portion thereof within an established period of time when a current to ground exceeds some predetermined value that is less than that required to operate the overcurrent protective device of the supply circuit. Ground-Fault Protection of Equipment: A system intended to provide protection of equipment from damaging line-to-ground fault currents by operating to cause a disconnecting means to open all ungrounded conductors of the faulted circuit. This protection is provided at current levels less than those required to protect conductors from damage through the operation of a supply circuit overcurrent device. Guarded: Covered, shielded, fenced, enclosed, or otherwise protected by means of suitable covers, casings, barriers, rails, screens, mats, or platforms to remove the likelihood of approach or contact by persons or objects to a point of danger. Hoistway: Any shaftway, hatchway, well hole, or other vertical opening or space in which an elevator or dumbwaiter is designed to operate. Identified: (As applied to Equipment.) Recognizable as suitable for the specific purpose, function, use, environment, application, etc., where described in a particular Code requirement. (See "Equipment.") (FPN): Suitability of equipment for a specific purpose, environment, or application may be determined by a qualified testing laboratory, inspection agency, or other organization concerned with product evaluation. Such identification may include labeling or listing. (See "Labeled" and "Listed.") Individual Branch Circuit: See "Branch Circuit, Individual." In Sight From (Within Sight From, Within Sight): Where this Code specifies that one equipment shall be "in sight from," "within sight from," or "within sight," etc., of another equipment, one of the equipments specified is to be visible and not more than 50 feet (15.24 m) distant from the other. Insulated Conductor: See under "Conductor." Intermittent Duty: See under "Duty." Interrupting Rating: The highest current at rated voltage that a device is intended to interrupt under standard test conditions. (FPN): Equipment intended to break current at other than fault levels may have its interrupting rating implied in other ratings, such as horsepower or locked rotor current. Isolated: Not readily accessible to persons unless special means for access are used. 70-12 NATIONAL ELECTRICAL CODE Labeled: Equipment or materials to which has been attached a label, symbol, or other identifying mark of an organization acceptable to the authority having jurisdiction and concerned with product evaluation, that maintains periodic inspection of production of labeled equipment or materials and by whose labeling the manufacturer indicates compliance with appropriate standards or performance in a specified manner. Lighting Outlet: An outlet intended for the direct connection of a lampholder, a lighting fixture, or a pendant cord terminating in a lampholder. Listed: Equipment or materials included in a list published by an organization acceptable to the authority having jurisdiction and concerned with product evaluation, that maintains periodic inspection of production of listed equipment or materials, and whose listing states either that the equipment or material meets appropriate designated standards or has been tested and found suitable for use in a specified manner. (FPN): The means for identifying listed equipment may vary for each organization concerned with product evaluation, some of which do not recognize equipment as listed unless it is also labeled. The authority having jurisdiction should utilize the system employed by the listing organization to identify a listed product. Location: Damp Location: Partially protected locations under canopies, marquees, roofed open porches, and like locations, and interior locations subject to moderate degrees of moisture, such as some basements, some barns, and some cold-storage warehouses. Dry Location: A location not normally subject to dampness or wetness. A location classified as dry may be temporarily subject to dampness or wetness, as in the case of a building under construction. Wet Location: Installations underground or in concrete slabs or masonry in direct contact with the earth, and locations subject to saturation with water or other liquids, such as vehicle washing areas, and locations exposed to weather and unprotected. Multioutlet Assembly: A type of surface or flush raceway designed to hold conductors and receptacles, assembled in the field or at the factory. Multiwire Branch Circuit: See "Branch Circuit, Multiwire." Nonautomatic: Action requiring personal intervention for its control. (See "Automatic.") (FPN): As applied to an electric controller, nonautomatic control does not necessarily imply a manual controller, but only that personal intervention is necessary. Nonincendive Circuit: A circuit in which any arc or thermal effect produced, under intended operating conditions of the equipment or due to opening, shorting, or grounding of field wiring, is not capable, under specified test conditions, of igniting the flammable gas, vapor, or dust-air mixture. (FPN): For test conditions, see Electrical Equipment for Use in Class I, Division 2 Hazardous (Classified) Locations, ANSI/ISA-S12.12. ARTICLE 100 - DEFINITIONS 70-13 Outlet: A point on the wiring system at which current is taken to supply utilization equipment. Outline Lighting: An arrangement of incandescent lamps or electricdischarge lighting to outline or call attention to certain features such as the shape of a building or the decoration of a window. Oven, Wall-Mounted: An oven for cooking purposes designed for mounting in or on a wall or other surface and consisting of one or more heating elements, internal wiring, and built-in or separately mountable controls. (See "Cooking Unit, Counter-Mounted.") Overcurrent: Any current in excess of the rated current of equipment or the ampacity of a conductor. It may result from overload (see definition), short circuit, or ground fault. (FPN): A current in excess of rating may be accommodated by certain equipment and conductors for a given set of conditions. Hence the rules for overcurrent protection are specific for particular situations. Overload: Operation of equipment in excess of normal, full-load rating, or of a conductor in excess of rated ampacity that, when it persists for a sufficient length of time, would cause damage or dangerous overheating. A fault, such as a short circuit or ground fault, is not an overload. (See "Overcurrent.") Panelboard: A single panel or group of panel units designed for assembly in the form of a single panel; including buses, automatic overcurrent devices, and equipped with or without switches for the control of light, I heat, or power circuits; designed to be placed in a cabinet or cutout box placed in or against a wall or partition and accessible only from the front. (See "Switchboard.") Periodic Duty: See under "Duty." Plenum: A compartment or chamber to which one or more air ducts are connected and that forms part of the air distribution system. Power Outlet: An enclosed assembly that may include receptacles, circuit breakers, fuseholders, fused switches, buses, and watt-hour meter mounting means; intended to supply and control power to mobile homes, recreational vehicles, or boats; or to serve as a means for distributing power required to operate mobile or temporarily installed equipment. Premises Wiring (System): That interior and exterior wiring, including power, lighting, control, and signal circuit wiring together with all of their associated hardware, fittings, and wiring devices, both permanently and temporarily installed, that extends from the service point of utility conductors or source of a separately derived system to the outlet(s). Such wiring does not include wiring internal to appliances, fixtures, motors, controllers, motor control centers, and similar equipment. Qualified Person: One familiar with the construction and operation of the equipment and the hazards involved. 70-14 NATIONAL ELECTRICAL CODE Raceway: An enclosed channel designed expressly for holding wires, cables, or busbars, with additional functions as permitted in this Code. (FPN): Raceways may be of metal or insulating material, and the term includes rigid metal conduit, rigid nonmetallic conduit, intermediate metal conduit, liquidtight flexible conduit, flexible metallic tubing, flexible metal conduit, electrical nonmetallic tubing, electrical metallic tubing, underfloor raceways, cellular concrete floor I busways. raceways, cellular metal floor raceways, surface raceways, wireways, cablebus, and Rainproof: So constructed, protected, or treated as to prevent rain from interfering with the successful operation of the apparatus under specified test conditions. Raintight: So constructed or protected that exposure to a beating rain will not result in the entrance of water under specified test conditions. Readily Accessible: (See "Accessible, Readily.") Receptacle: A receptacle is a contact device installed at the outlet for the connection of a single attachment plug. (FPN): A single receptacle is a single contact device with no other contact device on the same yoke. A multiple receptacle is a single device containing two or more receptacles. installed. Receptacle Outlet: An outlet where one or more receptacles are Remote-Control Circuit: Any electric circuit that controls any other circuit through a relay or an equivalent device. Sealable Equipment: Equipment enclosed in a case or cabinet that is provided with a means of sealing or locking so that live parts cannot be made accessible without opening the enclosure. The equipment may or may not be operable without opening the enclosure. Separately Derived System: A premises wiring system whose power is derived from generator, transformer, or converter windings and that has no direct electrical connection, including a solidly connected grounded circuit conductor, to supply conductors originating in another system. Service: The conductors and equipment for delivering energy from the electricity supply system to the wiring system of the premises served. Service Cable: Service conductors made up in the form of a cable. Service Conductors: The supply conductors that extend from the street main or from transformers to the service equipment of the premises supplied. Service Drop: The overhead service conductors from the last pole or other aerial support to and including the splices, if any, connecting to the service-entrance conductors at the building or other structure. ARTICLE 100 - DEFINITIONS 70-15 Service-Entrance Conductors, Overhead System: The service conductors between the terminals of the service equipment and a point usually outside the building, clear of building walls, where joined by tap or splice to the service drop. Service-Entrance Conductors, Underground System: The service conductors between the terminals of the service equipment and the point of connection to the service lateral. (FPN): Where service equipment is located outside the building walls, there may be no service-entrance conductors, or they may be entirely outside the building. Service Equipment: The necessary equipment, usually consisting of a circuit breaker or switch and fuses, and their accessories, located near the point of entrance of supply conductors to a building or other structure, or an otherwise defined area, and intended to constitute the main control and means of cutoff of the supply. Service Lateral: The underground service conductors between the street main, including any risers at a pole or other structure or from transformers, and the first point of connection to the service-entrance conductors in a terminal box or meter or other enclosure with adequate space, inside or outside the building wall. Where there is no terminal box, meter, or other enclosure with adequate space, the point of connection shall be considered to be the point of entrance of the service conductors into the building. Service Point: Service point is the point of connection between the facilities of the serving utility and the premises wiring. Setting (of Circuit Breaker): See under "Circuit Breaker." Short-Time Duty: See under "Duty." Show 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. Sign: See "Electric Sign." Signaling Circuit: Any electric circuit that energizes signaling equipment. Solar Photovoltaic System: The total components and subsystems that, in combination, convert solar energy into electrical energy suitable for connection to a utilization load. Special Permission: The written consent of the authority having jurisdiction. Switchboard: A large single panel, frame, or assembly of panels on which are mounted, on the face or back, or both, switches, overcurrent and other protective devices, buses, and usually instruments. Switchboards are generally accessible from the rear as well as from the front and are not intended to be installed in cabinets. (See "Panelboard.") 70-16 NATIONAL ELECTRICAL CODE Switches: Bypass Isolation Switch: A bypass isolation switch is a manually operated device used in conjunction with a transfer switch to provide a means of directly connecting load conductors to a power source, and of disconnecting the transfer switch. General-Use Switch: 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. General-Use Snap Switch: A form of general-use switch so constructed that it can be installed in flush device boxes or on outlet box covers, or otherwise used in conjunction with wiring systems recognized by this Code. Isolating Switch: A switch intended for isolating an electric 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. Motor-Circuit Switch: A switch, rated in horsepower, capable of interrupting the maximum operating overload current of a motor of the same horsepower rating as the switch at the rated voltage. Transfer Switch: A transfer switch is a device for transferring one or more load conductor connections from one power source to another. (FPN): A transfer switch may be either automatic or nonautomatic. Thermally Protected: (As applied to motors.) The words "Thermally Protected" appearing on the nameplate of a motor or motor-compressor indicate that the motor is provided with a thermal protector. Thermal Protector: (As applied to motors.) A protective device for assembly as an integral part of a motor or motor-compressor that, when properly applied, protects the motor against dangerous overheating due to overload and failure to start. (FPN): The thermal protector may consist of one or more sensing elements integral with the motor or motor-compressor and an external control device. Utilization Equipment: Equipment that utilizes electric energy for electronic, electromechanical, chemical, heating, lighting, or similar purposes. Varying Duty: See under "Duty." Ventilated: Provided with a means to permit circulation of air sufficient to remove an excess of heat, fumes, or vapors. Volatile Flammable Liquid: A flammable liquid having a flash point below 38°C (100°F), or a flammable liquid whose temperature is above its flash point, or a Class II combustible liquid having a vapor pressure not exceeding 40 psia (276 kPa) at 38°C (100°F) whose temperature is above its flash point. Voltage (of a Circuit): The greatest root-mean-square (effective) difference of potential between any two conductors of the circuit concerned. (FPN): Some systems, such as 3-phase 4-wire, single-phase 3-wire, and 3-wire direct-current may have various circuits of various voltages. ARTICLE 100 - DEFINITIONS 70-17 Voltage, Nominal: A nominal value assigned to a circuit or system for the purpose of conveniently designating its voltage class (e.g., 120/240, 480Y/277, 600). The actual voltage at which a circuit operates can vary from the nominal within a range that permits satisfactory operation of equipment. (FPN): See Voltage Ratings for Electric Power Systems and Equipment (60 Hz), ANSI C84.1-1989. Voltage to Ground: For grounded circuits, the voltage between the given conductor and that point or conductor of the circuit that is grounded; for ungrounded circuits, the greatest voltage between the given conductor and any other conductor of the circuit. Watertight: So constructed that moisture will not enter the enclosure under specified test conditions. (FPN): For test conditions other than for rotating equipment, see Enclosure for Electrical Equipment (1000 Volts Maximum), Section 250-5.07, Hosedown Test, NEMA Standards Publication No. 250-1979. Weatherproof: So constructed or protected that exposure to the weather will not interfere with successful operation. (FPN): Rainproof, raintight, or watertight equipment can fulfill the requirements for weatherproof where varying weather conditions other than wetness, such as snow, ice, dust, or temperature extremes, are not a factor. Wet Location: See under "Location." B. Over 600 Volts, Nominal Whereas the preceding definitions are intended to apply wherever the terms are used throughout this Code, the following definitions are applicable only to parts of the article specifically covering installations and equipment operating at over 600 volts, nominal. Circuit Breaker: See under "Switching Devices." Cutout: See under "Switching Devices." Disconnect (Isolator): See under "Switching Devices." Disconnecting Means: See under "Switching Devices." Fuse: An overcurrent protective device with a circuit opening fusible part that is heated and severed by the passage of overcurrent through it. (FPN): 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. Expulsion 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, extinguishes the arc. Power 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. Vented Power Fuse: A fuse with provision for the escape of arc gases, liquids, or solid particles to the surrounding atmosphere during circuit interruption. 70-18 NATIONAL ELECTRICAL CODE Nonvented Power Fuse: A fuse without intentional provision for the escape of arc gases, liquids, or solid particles to the atmosphere during circuit interruption. Controlled Vented Power Fuse: A fuse with provision for controlling discharge circuit interruption such that no solid material may be exhausted into the surrounding atmosphere. (FPN): 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 conduction members in the path of the discharge where the distance between the vent and such insulation or conduction members conforms to manufacturer's recommendations. Interrupter Switch: See under "Switching Devices." Multiple Fuse: An assembly of two or more single-pole fuses. Oil (Filled) Cutout: See under "Switching Devices." Power Fuse: See under "Fuse." Regulator Bypass Switch: See under "Switching Devices." Switching Device: A device designed to close, open, or both, one or more electric circuits. Switching Devices: Circuit Breaker: A switching device capable of making, carrying, and breaking currents under normal circuit conditions, and also making, carrying for a specified time, and breaking currents under specified abnormal circuit conditions, such as those of short circuit. Cutout: 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. Disconnecting (or Isolating) Switch (Disconnector, Isolator): A mechanical switching device used for isolating a circuit or equipment from a source of power. Disconnecting Means: A device, group of devices, or other means whereby the conductors of a circuit can be disconnected from their source of supply. Interrupter Switch: A switch capable of making, carrying, and interrupting specified currents. Oil 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. Oil Switch: An oil switch is a switch having contacts that operate under oil (or askarel or other suitable liquid). Regulator Bypass Switch: A specific device or combination of devices designed to bypass a regulator.