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Basic Insulation Level (BIL) - A reference insulation level expressed as the impulse crest voltage of the nominal 1.2 x 50 microsecond wave. This is a measure of the ability of the insulation to withstand very high voltage surges.

Cellular Floor - An assembly of cellular metal or cellular concrete floor members, consisting of units with hollow spaces (cells) suitable for use as raceways and, in some cases, non-cellular units.

Full Range - A current-limiting fuse capable of interrupting all currents from the maximum rated interrupting current down to the minimum continuous current that causes melting or the fusible element(s), when the fuse is applied at maximum ambient temperature specified by the fuse manufacturer.

Eventful Failure - Any electrical failure that would result in: extensive apparatus damage and need for repair; the spilling of hot and/or environmentally damaging fluids; that which could result in loss of a human life; catastrophic failure; violent failure; any electrical failure that is accomplished by a visible demonstration and may include tank rupture, damage bushings or loosened cover.

Fault Close Rating - The ability of a switching device to close into a fault current of a specific magnitude without excessive arcing.

Fault Current - The current from the connected power system that flows in a short circuit.

Fault Indicator - A device which indicates fault current by sensing the magnetic field caused by current flowing through the conductor. Once the current is above the fault indicator's current rating, the fault indicator will trip.

FCC Insulating End - An insulator designed to electrically insulate the exposed ends of Type FCC cables.

Fulgurite - A tunnel-like structure formed when a current-limiting fuse operates; glass-like structure formed by the temperature of a high voltage arc when a current-limiting fuse operates; the fused silica sand that remains after prolonged abnormal current flow.

Expulsion Fuse - A replaceable one-shot current interrupting device having definite time current characteristics; a device which has a metal melting element and uses the principles of heated fibers releasing de-ionizing gases, and alternating current passing through a zero reference periodically for arc extinction.

Ground Fault - Any undesired current path from a point of differing potential to ground.

Ground Fault Circuit Interrupter - A device whose function is to interrupt, within a predetermined time, the electrical circuit to the load 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.

Class A Ground Fault Circuit Interrupter (GFCI) - A protective device that will interrupt the circuit to the load when the ground fault current is 6 mA or more but not when the ground fault current is 4 mA or less (there will be a less then 10% current limit variation when the ambient air temperature is less than –5 °C or more than 40 °C) in a time

• (a) not greater than that given by the equation T = (20 / I)^1.63, where
  T is in seconds; and
  I is the ground fault current in rms milliamperes for fault currents between 4 mA and 260 mA; and
• (b) not greater than 25 ms for ground fault currents over 260 mA.

In addition, a Class A GFCI is to be capable of interrupting the circuit to the load, in keeping with the above requirements if the identified circuit conductor (neutral) becomes inadvertently grounded between the interrupter and the load. The prime function of a Class A GFCI is to provide protection against hazardous electric shocks from leakage current flowing to ground from defective circuits or equipment. It does not provide protection against shock if a person makes contact with two of the circuit conductors on the load side of the GFCI.

Class A GFCIs are marked “GROUND FAULT CIRCUIT INTERRUPTER CLASS A” or with an  abbreviated form such as “GFCI CL A”, “GFCI A”, or “CL A” where the area available for marking makes the complete text impracticable.

Impulse - A current surge.

Impulse Tests - Tests which ensure a satisfactory level of insulation and the ability of a device to withstand, within certain limits, overvoltage surges (such as lightning strikes) that may occur in service.

Insulated - Means separated from other conducting surfaces by a dielectric material or air space having a degree of resistance to the passage of current and to disruptive discharge sufficiently high for the condition of use.

Insulating as Applied to Non-Conducting Substances - Means that they are capable of bringing about the condition defined as insulated.

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.

Insulation Coordination - The review of the protective level of the arrester and the insulation level of the equipment to be protected to ensure that the arrester is adequately protecting the equipment.

Insulation System - A balanced combination of materials (kraft paper, oil, porcelain, etc.) which provides dielectric strength to a device.

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

Mineral-Insulated Cable - A cable having bare solid conductor(s) supported and insulated by a highly compressed refractory material enclosed in a liquid- and gas-tight metal tube sheathing; the term includes both the regular type (MI) and the light-weight type (LWMI) unless otherwise qualified.

Multi-Outlet Assembly - A surface or flush enclosure carrying conductors for extending one 2-wire or multi-wire branch circuit to two or more receptacles of the grounding type which are attached to the enclosure.

Multiple Section Mobile Unit - A single structure composed of separate mobile units, each towable on its own chassis, which, when towed to the site, are coupled together mechanically and electrically to form a single structure.

Multi-Winding Motor - A motor having multiple and/or tapped windings, intended to be connected or re-connected in two or more configurations, for operation at any one of two or more speeds and/or voltages.

Multi-Wire Branch Circuit - A branch circuit consisting of two or more ungrounded conductors having a voltage difference between them and an identified grounded conductor having equal voltage between it and each ungrounded conductor, with this grounded conductor connected to the neutral conductor.

Portable Ground Fault Circuit Interrupter - A ground fault circuit interrupter which is either of the direct plug-in type or specifically designed to receive current by means of a flexible cord or cable and an attachment plug and which incorporates one or more receptacles for the connection of equipment which is provided with a flexible cord or cable and an attachment plug.

Series/Multiple - A winding of two similar coils that can be connected for series operation or multiple (parallel) operation.

Solar AC Module - A complete, environmentally protected assembly of interconnected solar cells, inverter, and other components designed to generate ac power.

Solar Module - The smallest complete, environmentally protected assembly of interconnected solar cells.

Time to Impulse Sparkover - The time between virtual zero of the voltage impulse causing sparkover and the point on the voltage wave at which sparkover occurs.

UL / ULC - Underwriters’ Laboratories is an independent, not-for-profit, nongovernmental product safety organization responsible for product safety standards development, testing, and certification.
Underwriters' Laboratories USA / Underwriters' Laboratories of Canada

Vault - (transformer vault or electrical equipment vault) - An isolated enclosure, either above or below ground, with fire-resisting walls, ceilings, and floors for the purpose of housing transformers and other electrical equipment.

Voltage Regulation - For a transformer, the change in secondary voltage which occurs when the load is reduced from rated value to zero, with the values of all other quantities remaining unchanged. The regulation may be expressed in percent (or per unit) on the basis of the rated secondary voltage at full load.

Voltage Regulator - An electrical device on an electric system that keeps voltage which is supplied to customers at a constant level, usually around 120 volts, regardless of load fluctuations.