Learn About the Definitions of Electrical Terms



  1. noun
  2. The physical phenomena arising from the behavior of electrons and protons that is caused by the attraction of particles with opposite charges and the repulsion of particles with the same charge.
  3. The physical science of such phenomena.
  4. The electric current used or regarded as a source of power.
  5. Intense, contagious emotional excitement.

An older term for the nominal voltage for lights and portable appliances in homes. 120 would be a more accurate and up-to-date identification of this voltage.

An older term for the nominal voltage in a home for running some major appliances. 240 would be a more accurate and up-to-date identification of this voltage.

(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.

(As applied to equipment) Admitting close approach: not guarded by locked doors, elevation, or other effective means.

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.

Alternating Current (Advantages)
As compared with DC, the advantage of AC is the reduced cost of transmission by the use of high voltage transformers.

Alternating Currents (Disadvantages)
As compared with DC, the disadvantages of AC are: The high voltage which renders it dangerous and requires more efficient insulation; alternating current cannot be used for such purposes as electroplating, charging storage batteries, etc.

Alternating Current (Effects)
There are several effects of the AC to consider in determining the size of wires. Accordingly, allowance must be made for: Self-induction, mutual induction, power factor, skin effect, eddy currents, frequency, resistance, electric hysteresis, etc.

Alternating Currents
The term alternating current refers to a current that reverses at regularly recurring intervals of time and that has alternately positive and negative values.

Ambient Temperature
The temperature of the air, water, or surrounding earth. Conductor ampacity is corrected for changes in ambient temperature including temperatures below 86°F. The cooling effect can increase the current carrying capacity of the conductor.

An electric meter used to measure current, calibrated in amperes.

The current-carrying capacity of conductors or equipment, expressed in amperes.

Ampere is the electrical unit of electrical current. It measures the amount of electrical charge that flows in an electrical circuit per one second.

The positive pole of a battery, or preferably the path by which the current passes out and enters the electrolyte on its way to the other pole; opposed to the cathode.

A non lighting item that, by its resistance, consumes electricity rather than just passing it on. Therefore, an appliance is neither a fixture (for lighting) nor a device (for passing on). Examples: fax machine, garbage disposal, or even a wired-in smoke alarm.

Arc-Fault Interrupter
A circuit breaker (or receptacle) that can trip off for line-to-neutral arcing (which would not soon trip a standard breaker) or also for in-line (series) arcing.

Current passing (through air) across a gap, that is, using the air itself like a wire.

Bonding Jumper
A bare or insulated conductor used to ensure the required electrical conductivity between metal parts required to be electrically connected. Frequently used from a bonding bushing to the service equipment enclosure to provide a path around concentric knockouts in an enclosure wall: also used to bond one raceway to another.

Branch Circuit
The circuit conductors between the final overcurrent device protecting the circuit and the outlet(s).

An automatic switching device that disconnects power to a circuit when current or heat exceeds a certain level for a certain amount of time. It clips on to one or two live busbars in a panel box and passes this liveness through itself to the circuit wire(s) attached to it, normally by means of a screw(s). Its handle is generally in one of three positions: on, tripped (the middle position), and off.

A piece of rigid metal within a panel or fusebox that distributes electricity to the various circuits by means of their connection to it.

A cable is a set of wires, usually encased in an outer protective sheath. A cord would be a cable by this definition so far, but a cable is part of a permanent installation; a cord is more flexible and often has a plug end for a portable appliance or lamp. 2-wire cable, such as 14-2 and 12-2 (which indicate wire size) refers to a cable with two insulated wires, not counting any ground wire. Likewise, 3-wire cable has three insulated wires, with any ground being additional.

The French heat unit.

Measure, in farads, or the opposition to voltage changes in an AC circuit, causing voltage to lag behind current; exhibited by condensers, two conductors separated by a nonconductor.

Capacitive Reactance
The effect of capacitance in opposing the flow of alternating or pulsating current.

A device used to boost the voltage to a motor. Running capacitors are used in starting winding to increase the running torque of the motor. Starting capacitors are used in the starting winding to increase the starting torque of the motor. Two electrodes or sets of electrodes in the form of plates, separated from each other by an insulating material called the dielectric.

A complete path over which an electric current can flow.

Circuit (Series)
A circuit supplying energy to a number of devices connected in series. The same current passes through each device in completing its path to the source of supply.

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 injury to itself when properly applied within its rating. Circuit breakers can be reset.

Closed Circuit
A circuit permitting a continuous current.

An assemblage of successive convolutions of a conductor. A unit of a winding consisting of one or more insulated conductors connected in series and surrounded by common insulation, and arranged to link or produce magnetic flux.

The terminal of a three-way switch (or the wire attached to it) which makes internal contact with one or the other of the traveler terminals, depending on the position the switch is moved to.

The measure of ease with which a substance conducts electricity, measured in ohms. It is the opposite of resistance and is expressed in mhos.

An electrical path which offers comparatively little resistance. A wire or combination of wires not insulated from one another, suitable for carrying a single electric current. Busbars are also conductors. Conductors may be classed with respect to their conducting power as; (a) good; silver, copper, aluminum, zinc, brass, platinum, iron, nickel, tin, lead; (b) fair; charcoal and coke, carbon, plumbago, acid solutions, seawater, saline solutions, metallic ores, living vegetable substances, moist earth; (c) partial; water, the body, flame, linen, cotton, mahogany, pine, rosewood, lignum vitae, teak, and marble.

The state of being whole, unbroken.

Continuous Load
A load where the maximum current is expected to continue for three hours or more. Rating of the branch circuit protection device shall not be less than 125% of the continuous load.

A unit of electrical charge; the quantity of electricity passing in one second through a circuit in which the rate of flow is one ampere.

Any accidental contact between electric wires or conductors.

The flow of electrons in a wire (or other conductor). This is measured in amps (amperes). Because a house is provided with alternating current, the terms positive and negative do not apply as they do to direct current in batteries, cars, and such. Instead, in the case of 120-volt power, we tend to say that the power company is providing electricity that will flow to their neutral wire from the hot wire. This directional talk can be misleading since the actual electrons are moving back and forth sixty times per second.

The movement of electrons through a conductor; measured in amperes, milliamperes, and microamperes.

A complete reversal of alternating current, passing through a complete set of changes or motions in opposite directions, from a rise to maximum, return to zero, rise to maximum in the other direction, and another return to zero. One complete positive and one complete negative alternation of current or voltage.

Free from any electric connection to a source of potential difference and from electric charge. The term is used only with reference to current-carrying parts that are sometimes alive.

A Latin prefix often used with a physical unit to designate a quantity one-tenth of that unit.

Technically a measure of relative power levels; a measure of the loudness of a bell, siren, horn, or other noise; the strength of an audio signal.

The distance or angle by which one line departs from another.

Demand Factor
For an electrical system or feeder circuit, this is a ratio of the amount of connected load (in kva or amperes) that will be operating at the same time to the total amount of connected load on the circuit. An 80% demand factor, for instance, indicates that only 80% of the connected load on a circuit will ever be operating at the same time. Conductor capacity can be based on that amount of load.

As distinct from a fixture or appliance, an item which does not itself consume significant electricity but interrupts or passes it on in a particular fashion. For example, a switch, a receptacle, a thermostat, a breaker, a fuse.

A skeleton geometrical drawing, illustrating the principles of application of a mechanism.

Also rheostat. A switch able to dim its lights by altering the voltage it passes on. A dimmer normally gets warm when operating but will overheat if running more wattage than it is designed for.

A two-electrode electron tube containing an anode and a cathode. Diodes are used as rectifiers and detectors.

Direct Current
A unidirectional current. It may be constant or periodically fluctuating, as rectified alternating current.

Loss of electric energy as heat.

The voltage drop developed across a resistor due to the current flowing through it.

Constructed or protected so that dust will not interfere with its successful operation.

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

Duty, Continuous
A service requirement that demands operation at a substantially constant load for an indefinitely long time.

Duty, Intermittent
A service requirement that demands operation for alternate intervals of load and no load, load and rest, or load, no load, and rest.

Duty, Periodic
A type of intermittent duty in which the load conditions regularly reoccur.

Duty, Short Time
A requirement of service that demands operations at a substantially constant load for a short and definitely specified time.

Duty, Varying
A requirement of service that demands operation at loads, and for intervals of time, both of which may be subject to wide variation.

Symbol for voltage.

The ground; considered as a medium for completing an electric circuit.

Electric Circuit
The path (whether metallic or nonmetallic) of an electric current.

Electrical Horsepower
746 watts.

Electrical Units
In the practical system, electrical units comprise the volt, the ampere, the ohm, the watt, the watt-hour, the coulomb, the henry, the mho, the joule, and the farad.

A person who is versed in the knowledge of electricity (Jake Electric).

The destruction of life by means of electric current.

A magnet produced by passing an electric current through and insulated wire conductor coiled around a core of soft iron, as in the fields of a dynamo or motor.

Electromotive Force (EMF)
An energy-charge relation that results in electric pressure (voltage), which produces or tends to produce charge flow.

The smallest charge of negative electricity known.

Energy Efficiency
The efficiency of an electric machine measured in watt-hours or kilowatt-hours; the watt-hour efficiency.

Explosion Proof
Designed and constructed to withstand and internal explosion without creating an external explosion or fire.

Practical unit of electrostatic capacity in the electromagnetic system. A condenser is said to have a capacity of one farad if it will absorb one coulomb (that is, one ampere per second), of electricity when subjected to a pressure of one volt. The unit of capacitance.

Faraday Effect
A discovery made by Faraday that a wave of light polarized in a certain plane can be turned about by the influence of a magnet so that the vibrations occur in a different plane.

A measure of length equal to six feet, used chiefly in taking soundings, measuring cordage, etc.

A circuit, such as conductors in conduit or a busway run, which carries a large block of power from the service equipment to a sub-feeder panel or a branch circuit panel or to some point at which the block power is broken into smaller circuits.

Fiber Optics
Piping light is the science that deals with the transmission of light through extremely thin fibers of glass, plastic, or other transparent material.

Or luminaire. A nonportable electrically-produced light assembly; distinguished from appliance or device.

That property by virtue of which certain solids and fluids become luminous under the influence of radiant energy.

An elementary physical cause capable of modifying the motion of a mass.

A prescribed form, principle, or rule expressed in mathematical terms, chemical symbols, etc.

A rule or principle expressed in algebraic language.

The number of periods occurring in the unit of time-periodic processes, such as in the flow of electric charge. The number of complete cycles per second existing in any form of wave motion; such as the number of cycles per second of an alternating current.

A strip of wire or metal inserted in series with a circuit which, when it carries an excess of current over its rated capacity, will burn out. Also called a cutout.

Like a panel, a usual main source of the circuits in a home. It contains fuses rather than breakers.

A current indicator. It consists of a magnetic needle suspended within a coil of wire and free to swing over the face of a graduated dial. The movement of the needle shows the direction of the current and indicates whether it is a strong or weak one. There are numerous types of galvanometers such as astatic, tangent, sine, differential, ballistic, and D’Arsonval.

A combining of more than one device side-by-side, as, a three-gang switch box.

A general name given to a machine for transforming mechanical energy into electrical energy.

A ground-fault interrupter. A device to prevent electrocution, which serves also as a receptacle or (less commonly) as a breaker. I consider the letters GFCI confusing because they stand for ground-fault circuit interrupter and the word circuit is vague and distracting. GFI clearly states the function it performs: ground-fault interrupter. Since the 1973 Code has required GFI protection for more and more receptacle locations in homes. If connected to properly, a GFI receptacle is also able to sense and disrupt ground-faults at any standard receptacles wired on from it.

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.

The common reference point for the voltage of a home's electrical system. It refers to an intended or unintended connectedness to the earth. The neutral wires of circuits and of the system are grounded, but a ground wire means a separate grounding wire keeping metal parts of devices, fixtures, or appliances from staying accidentally energized and endangering people or equipment. Installed in homes since the 1960s, these wires are to be either bare or green-covered. The ground wire is not connected to be part of the normal path of the circuit, as a neutral is. When a ground wire does carry current, it is taking care of an otherwise dangerous situation; in fact, it is supposed to carry so much flow suddenly, that it causes the breaker of the circuit to trip, thereby also alerting us that a problem needs attention. If things were not grounded, people's bodies would more often be a path for current from a hot wire touching the metal to get to ground (without our having enough conductivity to trip a normal breaker!).

Ground Fault Circuit Interrupter
A device intended for personal protection that functions to de-energize a circuit or portion thereof within an established period of time when a current to ground exceeds some predetermined value that is less than required to operate the overcurrent protection 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 operations of a supply circuit overcurrent device.

The term ground is a generic term that may mean neutral, equipment grounding conductor, earth, center tap of a transformer, or two-pole generator winding. The term ground is too generic in meaning to be properly used in discussions of electricity as it may mean too many different things.

Connected to earth or to some conducting body that serves in place of the earth.

Grounded Conductor
A system or circuit conductor that is intentionally grounded, usually gray or white in color.

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.

Any short circuit finding at least some of its path to the earth by way of something other than the neutral wire. It is a leaking of current off the intended path. Most shocks are an example.

Grounded Fixture Wire
That grounded wire attached within and coming from the light fixture itself would be the ungrounded fixture wire (white or gray).

A Grounded Leg
White wire that serves only one ungrounded conductor (a.k.a. hot conductor).

Grounding Conductor
A conductor used to connect metal equipment enclosures and/or the system grounded conductor to a grounding electrode, such as the ground wire run to the water pipe at a service; also may be a bare or insulated conductor used to ground motor frames, panel boxes, and other metal equipment enclosures used throughout electrical systems. In most conduit systems, the conduit is used as the ground conductor.

Grounding Electrode
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.

Grounding Equipment Conductor
The conductor used to connect the non current-carrying metal parts of equipment, raceways, and other enclosures to the system grounded conductor, the grounding electrode conductor, or both, of the circuit at the service equipment or at the source of a separately derived system.

Heat (Electric)
The heat produced in a conductor by the passage of an electric current through it.

Hertz (HZ)
Hertz is the unit of frequency. It measures the number of cycles per second.

Horsepower (HP)
Unit used to express rate of work, or power. One horsepower=746 watts. Work done at the rate of 33,000 foot-pounds per minute or 550 foot-pounds per second.

Or live. (As an adjective:) Having electrical force (voltage) in relation to ground/earth, especially 120 volts. Hot is the term used because anything even slightly connected to ground (like us!) could get agitated as a path this force uses toward ground. (As a noun:) The wire/terminal/contact that is to be hot, especially the wire from a breaker to lights/appliances.

Having voltage in relation to ground, especially 120 volts.

Symbol for electric current.

The total opposition in which a circuit offers the flow of alternating current at a given frequency; a combination of resistance and reactance, measured in ohms.

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, the specified equipment is to be visible and not more than 50´ distant from the other.

The process by which an electrical conductor becomes electrified when near a charged body and becomes magnetized.

The intake or energy absorbed by a machine during its operation, as distinguished from the output of useful energy delivered by it.

A device for fastening and supporting a conductor. Glass and porcelain are employed almost universally for supporting overhead wires.

Interrupter Rating
The highest current at rated voltage that a device is intended to interrupt under standard test conditions.

An electrically charged atom or radical.

Jacobi’s Law
A law of electric motors which states that the maximum work of a motor is performed when its counter electromotive force is equal to one half the electromotive force expended on the motor.

The tying together of two single wire conductors so that the union will be good, both mechanically and electrically.

Is the unit of energy.

Joule’s Law
The law first stated by Joule, that the quantity of heat developed in a conductor by the passage of an electric current is proportional to the resistance of the conductor, to the square of the strength of the current, and to the duration of the flow.

A short piece of wire within a box, going between two wire nuts or between two devices' terminals. It passes a function (hot, switched, neutral) from one place to the other. A pigtail does this too but only goes from a wire nut to a device or fixture wire.

Junction Box
As distinguished from any electrical box, a box used only for making connections, not for also supporting a switch, receptacle, or light. The boxes for these others usually also have connections and splices in them in addition.

Kilovolt (KV)
A unit of pressure equal to one thousand volts.

A unit of electrical power, equal to one thousand watts. Electric power is usually expressed in kilowatts. As the watt is equal to 1/746 horsepower, the kilowatt or 1,000 watts = 1.34 hp. Careful distinction should be made between kilowatts and kilovolt amperes.

The symbol for inductance.

Items to which a label, trademark, or other identifying mark of nationally recognized testing labs has been attached to identify the items as having been tested and meeting appropriate standards.

The escape of electric current through defects in insulation or other causes.

Line and Load
These are relative terms. In relation to a given switch or device, line refers to wires or voltage being supplied to it from upstream or from the direction of the main service panel. With regard to the same device, load refers to wires (or terminals) that are downstream from or controlled by it. So wires from a switch or GFI might be load wires with respect to that switch but line wires with respect to another switch downstream from it. Another use of the term load is to refer to the energy user(s) along the circuit's path, such as a light or appliance. By providing resistance, these items limit current and, in the process, do useful things.

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.

Location, Damp
A location subject to a moderate amount of moisture such as some basements, barns, cold storage, warehouses, and the like.

Location, Dry
A location not normally subject to dampness or wetness: a location classified as dry may be temporarily subject to dampness or wetness, as in the case of a building under construction.

Location, Wet
A location subject to saturation with water or other liquids.

Power expended without accomplishing useful work.

Made Circuit
A closed or completed circuit.

A unit of electrical resistance equal to one million ohms.

An instrument for measuring extremely high resistance.

A unit of pressure equal to one million volts.

A test instrument for measuring the insulation resistance of conductors and other electrical equipment; specifically, a megohm (million ohms) meter; this is a registered trademark of the James Biddle Co.

An electric indicating instrument as a voltmeter, ammeter, etc.

The opposite of positive. A potential less than that of another potential or of the earth. In electrical apparatus, the pole or direction toward which the current is supposed to flow.

An electric circuit in which the parts are connected in some special manner and cannot be classed as in series, in parallel, or in series-parallel.

White wire that carries the unbalance load between two hot (ungrounded conductor). A neutral must be serving two ungrounded conductors (a.k.a. hot conductor) that read 240 volts between those two ungrounded (hot) conductors.

A proton and an electron in very close union existing in the nucleus. A particle having the weight of a proton but carrying no electric charge. It is located in the nucleus of an atom.

Noninductive Circuit
A circuit in which the magnetic effect of the current flowing has been reduced by one or several methods to a minimum or to zero.

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

The unit of electrical resistance. Resistance is one ohm when a DC voltage of one volt will send a current of one ampere through.

Ohm (symbol Ω) is the electrical unit of resistance. The Ohm unit was named after George Simon Ohm.

An instrument for measuring resistance in ohms. Take a look at this diagram to see how an ohmmeter is used to check a small control transformer. The ohmmeter's pointer deflection is controlled by the amount of battery current passing through the moving coil. Before measuring the resistance of an unknown resistor or electrical circuit, the ohmmeter must first be calibrated. If the value of resistance to be measured can be estimated within reasonable limits, a range selected that will give approximately half-scale deflection when the resistance is inserted between the probes. If the resistance is unknown, the selector switch is set on the highest scale. Whatever range is selected, the meter must be calibrated to read zero before the unknown resistance is measured.

(noun:) A physical discontinuity at some point along the path of some part of a circuit. Unlike an overload or short, an open involves current no longer being able to flow. This might be intentional, as when we turn a switch off, but in regard to troubleshooting an open is typically a break, gap, or deterioration.

Open Circuit
A circuit, the electrical continuity of which has been interrupted, as by opening a switch.

Technically, any point along a circuit where a light or appliance receives its final connections to the hot and neutral of the circuit. The outlet may consist of a receptacle for a cord to plug into, or it may be a box at which the item using the electricity is hard-wired. In practice, however, we usually mean a receptacle. The following are not outlets: switch, breaker, junction box.

The current, voltage, power, or driving force delivered by a circuit or device.

Overcurrent is any current load in excess of the safety rating of equipment or the ampacity of a conductor. Overcurrent may result from an overload, a short circuit, or a ground fault. Overcurrent does not always cause a fire.

Load greater than the load for which the system or mechanism was intended. A fault, such as a short circuit or ground fault, is not an overload.

Abbreviation for power.

Or panel box or breaker box. The large metal box containing breakers for circuits. The main panel or service panel would be the central source for the home and would be receiving its power from the power company. There can be subpanels in a home, fed from the main panel and containing some of the home's circuit breakers. Some people still use the term fuse box to refer to a panel, but that term should relate to something having fuses. The term panel could refer to either a breaker box or a fuse box.

A single panel or group of panel units designed for assembly in the form of a single panel: includes buses and may come with or without switches and/or automatic overcurrent protective devices for the control of light, heat, or power circuits of individual as well as aggregate capacity. It is designed to be placed in a cabinet or cutout box that is in or against a wall or partition and is accessible only from the front.

The maximum instantaneous value of a varying voltage or current.

Peak Current
The maximum value of an alternating current.

The time required for a complete cycle of alternating current or voltage; for 60 cycles per second, a period would be 1/60 second.

Phantom Voltage
An inconsequential voltage many testers will detect. It may register as a lower or a full voltage found on a wire that is connected neither to hot nor to neutral/ground. It seems to come about by means of capacitance or inductance from a hot wire that is near the unconnected wire over a good distance in the same cable.

Phantom Voltage With Phantom Load
Which is the consumption of electricity by a TV when it is plugged in but not turned on, or a charger when it is plugged in but not charging anything.

Descriptive of the effect that light has on electric circuits, through a device controlled by light.

A cable that has an appropriate connector on one end and loose wires on the other. It is designed to patch into an existing line or to terminate the ends of a long run.

Chamber or space forming a part of an air conditioning system.

The term used to describe a terminal with fewer electrons than normal so that it attracts electrons. Electrons flow into the positive terminals of a voltage source.

The rate at which work is done; it is usually expressed as the number of foot-pounds in one minute, that is, if you lift 33,000 foot-pounds in one minute, you have done 1 horsepower of work.

The smallest quantity of electricity which can exist in the free state. A positively charged particle in the nucleus of an atom.

A switch or circuit breaker that has a high contact opening speed.

Symbol for resistance.

So constructed, projected, or treated as to prevent rain from interfering with the successful operation of the apparatus under specified test conditions.

So constructed or protected that exposure to a beating rain will not result in the entrance of water.

Opposition offered to the flow of AC by the inductance or capacity of a part; measured in ohms.

Also plug-in; or, loosely, outlet or plug. A device that serves as the outlet for lights or appliances to connect to a circuit by means of a cord with a plug on the end.

Recovery Voltage
The voltage impressed upon the fuse after a circuit is cleared.

An electromagnetic device which permits control of current in one circuit by a much smaller current in another circuit.

The opposition offered by a substance or body to the passage through it of an electric current which converts electric energy into heat. Resistance is the reciprocal of conductance.

Resistance Drop
The voltage drop in place with the current.

An aggregation of one or more units possessing the property of electrical resistance. Resistors are used in electric circuits for the purpose of operation, protection, or control.

A name given to substances having only moderate power of transmitting electricity, and which may be said in that respect to stand midway between conductors and insulators.

Separately Derived System
A premises wiring system whose power is derived from a battery, a solar photovoltaic system, or from a generator, transformer, or converter windings, and that has no direct electrical connection, including solidly connected grounded circuit conductor, to supply conductors originating in another system.

Series Circuit
A circuit supplying energy to a number of loads connected in series, that is, the same current passes through each load in completing its path to the source of supply.

Series Parallel Circuit
An electric current containing groups of parallel-connected receptive devices, the groups being arranged in the circuit in series; a series multiple circuit.

Service Conductors
The supply conductors that extend from the street main or transformers to the service equipment of the premises being supplied.

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

Service Entrance Conductors
(Overhead) 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) The service conductors between the terminals of the service equipment and the point of connection to the service lateral.

Service Equipment
The necessary equipment, usually consisting of a circuit breaker or switch and fuses and their accessories, located near the point entrance of supply conductors to a building and intended to constitute the main control and cutoff means for the supply to the building.

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, 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 is the entrance point of the service conductors into the building.

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

Short Circuit
A fault in an electric circuit or apparatus due usually to imperfect insulation, such that the current follows a by-path and inflicts damage or is wasted.

Also lamp holder. The part of a light fixture that receives the bulb or tube. It is understandable that some people use socket to mean the receptacles we plug cords into because in both cases the one thing is receiving the other thing that actually uses up electricity.

A spiral of conducting wire, wound cylindrically so that when an electric current passes through it, its turns are nearly equivalent to a succession of parallel circuits, and it acquires magnetic properties similar to those of a bar magnet.

A discharge of electricity across a gap between two electrodes. The discharge is accompanied by heat and incandescence. Distinguish between spark and arc.

An unanchored electrical connector joining two or more wires directly. Compare terminal.

Steady Current
An electric current of constant amperage.

Submain Breaker
One of up to six (double) circuit breakers allowed until 1985 to be the means for disconnecting all power to a home's circuits. Since then, a single main breaker has been the required means.

A device used to interrupt continuity and current to part of a circuit.

Switch, General-Use Snap
A type of general-use switch so constructed that it can be installed in flush device boxes or on outlet covers, or otherwise used in conjunction with wiring systems recognized by the National Electric Code.

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

Switch, Knife
A switch in which the circuit is closed by a moving blade engaging contact clips.

Switch, Motor-Circuit
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.

Switch, Transfer
A transfer switch is 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 having switches, over current, and other protective devices, buses, and usually instruments mounted on the face, back, or both. Switchboards are generally accessible from the rear and from the front and are not intended to be installed in cabinets.

Switch Leg
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.

Tesla Coil
A form of induction coil designed by Tesla for obtaining high voltages and frequencies; it consists of a primary of a few turns of coarse wire and a secondary of fine wire, both immersed in oil insulation; a Tesla transformer.

A screw or other pressure-device to which one or more wires are connected for passing electrical continuity and current along. Like a splice, but a terminal is anchored to a larger structure, whereas a splice is free floating.

Although there is a type of light bulb and socket by this name, here we mean a switching system in which a light(s) is controllable from more than one location by two or more switches. The name comes from the usual number of terminals on or contact points within the switches involved.

An apparatus used for changing the voltage and current of an alternating circuit. A transformer consists of primary winding, secondary winding, and an iron core. In principle, if a current is passed through a coil of wire encircling a bar of soft iron, the iron will become a magnet; when the current is continued the bar loses its magnetization.

An active semiconductor device with three or more terminals. Transistors turn on instantly. They do not require a warm-up time like a tube does. A transistor will last for years and very little voltage is needed.

The pair of wires in a three-way switch system that is run (within the same cable) from one switch device to the next, attaching at each.

Ungrounded Fixture Wire
That hot wire attached within and coming from the light fixture itself would be the ungrounded fixture wire (any color in the rainbow BUT white, gray, green, or bare).

Ungrounded Conductor
(Any color in rainbow but white, gray, bare or green) serving a receptacle or any other electrical device is an ungrounded leg (a.k.a. hot conductor). That white wire serving a 220-volt oven with two ungrounded conductors (a.k.a. hot wires) measuring 240 volts between the two ungrounded conductors (a.k.a. hot wires) then that white wire is a true neutral (a.k.a. neutral conductor).

Unit of Current
The practical unit of current is the ampere, which is the current produced by a pressure of one volt in a circuit having a resistance of one ohm.

Unit of Electric Work
The joule.

Unit of Pressure
The volt, or pressure which will produce a current of one ampere against a resistance of one ohm.

Unit of Resistance
The ohm, which is the resistance that permits a flow of one ampere when the impressed pressure is one volt.

Symbol for volt.

The practical unit of electric pressure. The pressure that will produce a current of one ampere against a resistance of one ohm.

Voltage, also called electromotive force, is a quantitative expression of the potential difference in charge between two points in an electrical field.

Voltage Drop
The drop of pressure in an electric circuit due to the resistance of the conductor.

VOM Meter
A multimeter or a multitester, also known as a VOM (Volt-Ohm meter or Volt-Ohm-milliammeter), is an electronic measuring instrument that combines several measurement functions in one unit. A typical multimeter would include basic features such as the ability to measure voltage, current, and resistance.

Symbol for wattage.

So constructed that water or moisture will not enter the enclosure under specified test conditions.

Watt is the electrical unit of electric power. It measures the rate of consumed energy.

Rate of electric energy used by lights or appliances. When applied to devices, it indicates the maximum watts the device is designed to deliver or control (rather than use). Wattage is directly proportional to current and to voltage and is mathematically the product of them (amps x volts). 120 volts driving 15 amps through a resistance means 1800 watts are being used.

So constructed or protected that exposure to the weather will not interfere with successful operation.

A wire is a bendable metal for carrying electric current. Except when used as a grounding wire, it is coated with insulation material.

Y Connection
This method of transformer connection consists in connecting both the primaries and secondaries in star grouping.

Symbol for impedance.