AL - Aluminum

Alternating Current (ac) - A flow of electricity which reaches maximum in one direction, decreases to zero, then reverses itself and reaches maximum in the opposite direction. The cycle is repeated continuously. The number of cycles per second is equal to the frequency.

Ambient Temperature - The temperature of the atmosphere of surrounding environment. Typically defined by industry standards as 25° C.

Amp (Ampere) - A unit that measures the strength/rate of flow of electrical current.

ANSI - American National Standards Institute; Electrical standard developed and published as a result of recommended practices and studies made by NEMA and IEEE.

Arc - Sparking that results when undesired current flows between two point of differing potential.

Arc Voltage - The reaction of a circuit''s inductance to the rate of current change in the circuit; E = L(di/dt); when a current-limiting fuse operates, there is an associated arc voltage on the system.

Armored Cable - Electrical wires protected by metal sheathing.

Arrester - A protective device for limiting surge voltages on equipment by diverting surge current and returning the device to its original status. It is capable of repeating these functions as specified.

Aught - Standard conductor size, i.e. 4 aught designation 4/0.

Branch Circuits - The circuits in a house that branch from the service panel to boxes and devices.

Breakdown Voltage - Voltage at which material fails.

Breaker - A switch-like device that connects/disconnects power to a circuit.

Buss Bar - Separate, metallic strips that extend through the service panel. Breakers slide onto the "hot" busses and neutral and ground wires screw down in their respective busses.

BX Cable - An old type of armored cable now illegal.

Cable Clamps - Metal clips inside an electrical box that hold wires in place

Capacitor - An electrical device used to store electrical energy, and to release it back into the power system when required.

Circuit - A continuous loop of current (i.e. incoming "hot" wire, through a device, and returned by "neutral" wire).

Circuit Breaker - The most common type of "overcurrent protection." A breaker trips when a circuit becomes overloaded or shorts out.

Conductor - Any material which allows electrons to flow through it.

Conduit - A protective metal tube that wires run through.

CU - Copper

Current - The movement of electrons through a conductor, measured in amperes.

Current Interrupter - Any device that will open a circuit after sensing an abnormal high-circuit condition; a general name given to all types of fuses, reclosers and breakers.


Direct Current (dc) - An essentially constant value current that flows in only on direction.

Duplex Receptacle - The commonly used receptacle (outlet). Called "duplex" because it has two plug-in sockets.

Fixture - Any permanently connected light or other electrical device that consumes power.

Flicker - Impression of fluctuating brightness or color, occurring when the frequency of the observed variation lies between a few hertz and the fusion frequencies of the images.

Fluctuation - A surge dip in voltage amplitude, often caused by load switching or fault clearing.

Frequency - On ac circuits, the designated number of times per second that polarity alternates from positive to negative and back again, expressed in Hertz (Hz)

Fuse Arcing Time - The amount of time required of the fuse to extinguish the arc and clear the circuit; the specific amount of time required for an interrupter to clear a circuit after its fusible element has melted.

Fuses - Removable devices that will heat up, melt and electrically open the circuit after a period of prolonged abnormal current flow. Link a circuit at the fuse box. Fuse connections blow apart and break the circuit if an overload or short occurs.


GFCI or GFI (Ground Fault Circuit Interrupter) - A specific type of circuit protection (commonly required in kitchens & bathrooms) that helps safeguard against shocks. GFCI protection can come from an outlet or a breaker.

Ground Fault - Current misdirected from the hot (or neutral) lead to a ground wire, box, or conductor.

Grounds or Grounding - Connecting one side or neutral of a circuit to the earth through low resistance or low impedance paths, to help prevent transmitting shocks to personnel.

Hertz (Hz) - Expression of ac frequency in cycles per second, e.g., 60 Hz.

High Voltage and Low Voltage Windings - Terms used to distinguish the winding having the greater voltage rating from that having the lesser in two-winding transformers. The terminations on the high voltage windings are identified by H1, H2, etc., and on the low voltage by X1, X2, etc.

Hot, Neutral, Ground - The three most common circuit wires. The hot brings the current flow in, the neutral returns it to the source, and the ground is a safety route for returning current. The ground and neutral are joined only at the main service panel.

HV - High voltage

Impedance - The obstruction to the flow of current in an ac circuit. The transformer impedance is made up of the internal resistance and reactance which creates a voltage drop caused by current flowing in the windings. Impedance losses are a combination of heat (I2R) losses in the conductor, eddy current loss, and losses in other parts of the transformer caused by stray currents.

Impulse - A current surge

Insulation - A material having a high resistance to the flow of electric current; insulation over underground conductor is made of either EPR or XLPE material.

Insulator - Any material which does not allow electrons to flow through it.


Junction (Electrical) Box - A square, octagonal, or rectangular plastic or metal box that fastens to framing and houses wires, and/or receptacles and/or switches.

Knockout - A removable piece of an electrical box or panel that''s "knocked out" to allow cable to enter the box.

kVA - The kVA, or Kilovolt-ampere, output rating designates the output which a transformer can deliver for a specified time at rated secondary voltage and rate frequency without exceeding the specified temperature rise (1 kVA = 1000 VA)

kW - Kilowatts. Real power delivered to a load (W x 1,000 VA)

Lead - The short length of a conductor that hangs free in a box or service panel. (i.e. a wire end)

Load - The load of a transformer is the power, in kVA or volt-amperes, supplied by the transformer. Lagging Load: inductive type load. Leading Load: capacitive load.


Neutral - The junction point of the legs in a Wye circuit.

Neutral Grounding Resistor - A grounding device, the principal element of which is resistance, which is used to connect the neutral point of the transformer to earth.

NM - Nonmetallic-sheathed (plastic).

NMC - Solid plastic nonmetallic-sheathing used in wet or corrosive areas, but not underground (see UF).

Normal Duty - A lightning impulse classifying current category for distribution class arresters defined by ANSI/IEEE C62.11. A normal duty rated arrester has 5000 amperage impulse value crest (refer to heavy duty)

Ohm - A unit that measures the resistance a conductor has to electricity.

Ohm's Law - Voltage equals resistance multiplied by current.

Overvoltage - A voltage above the normal rated voltage or the maximum operating voltage of a device or circuit. A direct test overvoltage is a voltage above the peak of the line alternating voltage.


Phase - Classification of an ac circuit usually single-phase, two wire or three wire; two-phase, three wire or four wire; or three-phase, three wire or four wire.

Pigtail - A short, added piece of wire connected by a wire nut. Commonly used to extend or connect wires in a box.

Romex -  A brand name of nonmetallic-sheathed cable made by General Cable Corporation. Often mistakenly used as a collective term for NM sheathed cable.

Rough-In - Installing the boxes, cables, and making "in-wall" connections while the walls are still open. Later, final connections are made and the devices and appliances are installed during the trim-out.


Service Entrance (SE) - The location where the incoming electrical line enters the home.

Service Panel - The main circuit breaker panel (or fuse box) where all the circuits tie into the incoming electrical supply line.

Service/Supply Leads - The incoming electrical lines that supply power to the service panel.

Short Circuit - When current flows "short" of reaching a device. Caused by a hot conductor accidentally contacting a neutral or ground. A short circuit is an immediate fault to ground and should always cause the breaker to trip or the fuse to blow. (also see ground fault)

Surge -  Transient current or voltage associated with lightning or switching

Switchgear -  A general term covering switching and interrupting devices and their combination with associated control, metering, protective and regulating devices; also assemblies of these devices with associated interconnections, accessories, enclosures and supporting structures, used primarily in connection with the generation, transmission, distribution and conversion of electric power.

Three Phase Power - Three separate outputs from a single source. There is a phase difference of 120° between any two of the three voltages and currents.

Transformer - A static electrical device which by electromagnetic induction transfers electrical energy from one circuit to another circuit usually with changed values of voltage and current in the process.

Travelers - Wires that carry current between three-way and/or four-way switches.

Turn Ratio - The ratio of the number of turns in the high voltage winding to that in the low voltage winding.

UF (Underground Feeder) cable - Cable designed and rated for underground, outdoor use. Cable wires are molded into solid plastic.


Volt - A unit that measures the amount of electrical pressure.

Voltage -  Electric pressure; the force which causes current to flow through an electrical conductor.

Watt - A unit that measures the amount of electrical power.