Electrical Definitions


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Electrical Definitions

Letter - S

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.



The windings which receive the energy by induction from the primary.


Separately Derived System

A premises wiring system whose power is derived from a battery, from a solar photovoltaic system, or from a 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.



The conductors and equipment for delivering electric energy from the serving utility to the wiring system of the premises served.


Service Cable

Service conductors made up in the form of a cable.


Service Conductors

The conductors from the service point to the service disconnecting means.


Service Drop

Run of cables from the power company's aerial power lines to the point of connection to a customer's premises.


Service Equipment

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


Service Lateral

he 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, inside or outside the building wall. Where there is no terminal box, meter, or other enclosure, the point of connection is considered to be the point of entrance of the service conductors into the building.


Service Point

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


Service Raceway

The raceway that encloses the service-entrance conductors.


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.


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.


Signaling Circuit

Any electric circuit that energizes signaling equipment.



A term characterizing a circuit energized by a single alternating voltage source.


Slip Rings

The rotating contacts which are connected to the loops of a generator.


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.



The stationary coils of a generator.



That which is built or constructed.



A short duration high voltage condition.


Switch, Bypass Isolation

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


Switch, General-Use

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.


Switch, General-Use Snap

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


Switch, Isolating

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.


Switch, Motor-Circuit

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


Switch, Transfer

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



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



That part of a circuit run from a lighting outlet box where a luminaire or lamp-holder is installed down to an outlet box that contains the wall switch that turns the light or other load on or off: it is a control leg of the branch circuit.


Synchronous Motor

An alternating current motor which operates at the speed of rotation of the magnetic flux.