Technical Terms

Glossary of Terms

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

A

A - Abbreviation for amp(s)

AC - Abbreviation for alternating currents

ACB - Abbreviation for air circuit breaker

air circuit breaker (ACB) - Large circuit breaker typically used for high current, industrial applications

alternating current (AC) - A current that alternately flows in each of two direction. The time between current reversals is usually constant, producing a constant frequency. The waveform of current plotted against time is assumed to be symmetrical around zero, giving a sine wave. The term is normally only used to refer to the mains power supply.

Amps, ampere (A) - Unit of measure of electric current

Analogue signal - A signal which represents the size of another quantity, such as temperature or pressure, through the size of its own signal level.

ANSI - Abbreviation for American National Standards Institute. ANSI C2.41 is now designated IEEE C6241. See references.

AS - Abbreviation for Australian Standard

Asymmetrical - See common mode

Armouring - Protective metal covering, commonly incorporated on cables and often also used as an earth conductor on power cables

Arrester - Protection device, as in "Lightning Arrester". The term arrester is most commonly used to describe basic protectors for high-voltage overhead power lines.

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B

bandwidth - The band or range of frequencies which can be occupied by a signal. Signals outside the nominated bandwidth of a system may be distorted, loosing, or corrupting information

blackout - A total break in the supply lasting from several milliseconds to many hours. Also referred to as an outage or power cut.

bond - To connect metal parts of a system together so that they are at a common voltage, usually earth potential.

brownout - Sustained reductions in the supply voltage, lasting more than a few seconds. Also referred to as undervoltage.

BS - Abbreviation for British Standard

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C

CAD - Abbreviation for computer aided design

Capacitance - The property of isolated conductors to store an electrical charge. Capacitance can create limitations in the transmission of signals through circuits.

Capacitor - An electrical component which stores electrical charges. It consists of at least two metallic plates (conductors) separated by an insulator (a non-conducting dielectric material which may be solid, liquid, or gaseous). The capacitance of a given device depends upon the size and shape of the conductors, the distance between them, and the characteristics of the insulator. When used in conjunction with other components, it can provide a high-frequency filtering capability.

Capacitive Coupling - If an isolated conductor (or other electrical charge, such as lightning) is near to a second conductor, but is separated from it by air or some other insulator, the system forms a capacitor. An electric field is produced across the system creating a capacitive electrical path between the conductors. Also see coupling.

Category C, B, and A - Classes described by the ANSI Standard C62.41, which defines the surge waveforms that would be representative at various locations within a building. Category C products are intended for use at the main service panel or distribution panels that require large surge current handling capability. Category B defines mid-building, branch panel situations. Category A defines the local service panel or specific equipment.

CCTV - Abbreviation for closed-circuit television

Circuit breaker - A resettable alternative to the fuse, which created an open circuit under overcurrent or fault current conditions.

Clamping level - Describes to the voltage level that causes the surge suppression device to start to divert surge energy. A related, but more important parameter is the suppressed voltage.

Clean - Cable which is, supposedly, relatively free from interference

Closed-circuit television (CCTV) - A television system, other than broadcast television, which forms a closed circuit between television camera and receiver. CCTV has many commercial applications, eg. security systems.

Coaxial cable - A type of cable consisting of two concentric conductors separated by insulation, used to transmit high frequency (e.g.. television) signals.

Combination pulse - A high energy test pulse specified by ANSI C62.41-1999. Also called a "unipolar pulse".

Combination wave generator or hybrid generator - Transient test equipment designed to product voltage and/or current impulses of defined waveform.

Common mode - The voltage that appears between each of two or more conductors and earth. Also referred to as L-G and N-G.

Conductor - Material which electric current will easily pass through. Also, the set of wires, or conductors, which together from a power or data communication cable or supply. Power supplies typically consist of live/phase, neutral, and earth conductors. There is considerable variation in the names applied to the constituent conductors of data communication, signal, or telephone cable. Often there is one or more signal or line conductor(s) together with a screen and/or earth return conductor.

Conduit - A channel or pipe for mechanically protecting cables

Coupling - The interaction between two circuits which causes energy to be transferred from one to the other. This can be the result of capacitive, inductive, or resistive mechanisms

CP 326 - Code of practice (CP) superseded by BS 6651

Cross bond - To bond together two or more conductors

Cross coupling - see coupling

Current - The rate of flow of electrons through a conductor. Measured in amperes, or amp

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D

DC - Abbreviation for direct current

Delta supply - A three phase power supply with no neutral connection

Differential mode - The voltage that appears between two conductors, neither of which is at earth potential

Digital signal - A signal which operates with a smaller number, usually only two, voltage levels. Because only two easily distinguishable voltage levels are used, digital systems are free from many of the forms of distortion which affect analogue systems. Both can be affected by transient overvoltages.

Dip - A momentary reduction in the voltage for a duration from a half-cycle to a few seconds. Also referred to as a sag.

Direct current (DC) - A steady current in one direction, such as that provided by a battery, a dynamo, or the smoothed output of a rectifier circuit.

Dirty - Cable or supply carrying some form of interference

Discharge current - Refers to the transient current flowing through a protection device or component during operation.

Distribution board - A panel, enclosure, or'board" containing isolators, fuses, air circuit breakers, or protective devices; feeding one or more outgoing circuits and supplied by one or more incoming circuits, together with terminals of the neutral and earth combination. The term main, or main LV, distribution board refers to the building's principle distribution board, usually supplied directly form an electricity substation or HV to LV transformer. A sub distribution board describes a second tier distribution board supplied from the main distribution board and itself supplying either equipment or third tier distribution boards. The term local distribution board describes the unit that provides the power supply to a particular piece of equipment.

Diverter - General term for a protective device that diverts current away from a circuit

Draw wire - A high tension wire incorporated in many fiber optic and some other data cables, to enable the installer to pull the cable through inaccessible conduits or ducts.

Duct - A pipe or conduit for mechanically protecting cables

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E

Earth (Ground) - Any zero-voltage point. The earth itself is taken as being of zero voltage because its potential is not greatly affected by small currents. Conductors that connect equipment or circuits to earth or to an earth network are often referred to as earth.

Earth electrode - A conductor or group of conductors providing a good electrical connection the Earth (soil).

Earth leakage current - A stray current that flows to earth, in a circuit that is electrically sound. For safety reasons, the earth leakage current must be kept within prescribed limits.

Earth potential - Normally zero voltage

Earth reference - Connection to earth.

ECMA - Abbreviation for European Computer Manufacturers Association

Electric field - The field of force surrounding a charged object

Electrical noise - A signal frequency that may be riding on top of the power line sine wave. A number of systems use the power lines to carry signals and data to other locations. Attempts to filter out the "noise" may disrupt the current or future operation of these systems. Although it is seldom needed, it is wiser to provide line conditioning filtering immediately in front of sensitive equipment.

Electromagnetic compatibility (EMC) - A philosophy referring to attempts to prevent EMI. EMC practice dictates that potential sources of interference are designed so as not to affect equipment, and that potential victim equipment is designed to be immune from potential sources of interference.

Electromagnetic field - Combined electric field and magnetic field

Electromagnetic interference (EMI) - Electrically induces noise or transients

Electromagnetic pulse (EMP) - Pulses of energy caused by nuclear explosions and intense solar activity. EMP transients are much quicker (a faster rise time) than commonly occurring transients. Also called nuclear electromagnetic pulse (NEMP).

Electrostatic discharge (ESD) - Unlike NEMP or EMP, electrostatic discharge does not tend to be transmitted on power or data lines. An electrostatic charge is generated by two insulating objects being rubbed together. A charged object will discharge when it comes into contact with a conducting object.

EMC - Abbreviation for electromagnetic compatibility

EMI - Abbreviation for electromagnetic interference

EMP - Abbreviation for nuclear electromagnetic pulse

Energy - Maximum allowable energy (in joules) for a single impulse on a 10/1000 �s current waveform. Indicative of the maximum amount of energy that the suppressor can dissipate. This energy is dependent upon three variables: Voltage, Current, and Time. Any variation of the three will affect this figure.

Equipment transient design level - Term used in BS 6651:1992 to refer to the level at which a piece of equipment becomes susceptible to interference from transient overvoltages.

Equipotential - Of equal potential. This term is often used when describing a low resistance connection or bond between equipment and earth, made to ensure that the two points are always at the same voltage.

ESD - Abbreviation for electrostatic discharge

ETDL - Abbreviation for equipment transient design level

Ethernet - This is the product name of a particular form of local area network. It is governed by the standard IEEE 802.3 and operates over distances of up to around 2.5 km. Originally based upon a coaxial cable, the system can now also utilize twisted pair and fiber optic cable.

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F

Fiber optic cable - A non-conducting signaling medium which uses a light beam to transmit messages through a cable of thin filaments of glass or plastic. It is therefore unlike other types of cable which use an electric charge on conducting cable to transmit signals.

Filter - Consists of a combination of components that allows only certain frequencies, or a band of frequencies, to pass.

FIPS - Abbreviation for the American Federal Information Processing Standards body

Flash testing - A high voltage test to prove the integrity of electrical insulation

Flashover - A temporary breakdown of insulation, allowing a spark or discharge

Frequency - The number of times per second that an alternating voltage changes polarity from positive to negative. Measure in hertz (Hz). In the United States, the power line frequency is 60 Hz, or 60 cycles per second.

Fuse - Protective device that operates to create an open circuit under overcurrent or fault current conditions

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G

G - Abbreviation for giga, meaning 1,000,000,000 or 109. Used as a prefix to units such as frequency (Hz).

Gas discharge tube (GTD) - (also known as gas tube) is a hermetically sealed spark gap. It is an insulator until the voltage between its electrodes exceeds its breakdown voltage, at which point it arcs and crowbars the surge. The gas tube is filled with an inert gas (typically argon) and special low work function coatings, which are applied to the electrodes. As a result, a gas tube can take more surges with a stable predictable breakdown voltage, than an air gap.

Glitch - Voltage increases of no more than millisecond duration. Also referred to as transient overvoltages, spikes, and surges.

Ground - American term for earth, often denoted with a'G'. For safety reasons, electrical systems in the USA have a wire connected to earth ground at the service entrance. This'ground' wire is run along with the two current carrying wires.

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H

Harmonics - A continuous distortion of the normal sine wave, at frequencies of up to 3kHz.

Harmonic Distortion - The misshapen or distorted sinusoidal waveform resulting from the algebraic addition (to the fundamental wave shape) of higher frequency sine waves, which are multiples of the fundamental frequency. These multiples of the fundamental frequencies are denoted as harmonics. Algebraically adding the fundamental and the 3rd harmonic results in a harmonically distorted wave shape.

Headroom - The voltage difference between the peak of the 50/60 Hz power line sine wave voltage and the "Threshold Voltage" of the suppression device. A minimum spacing of 15%above the sine wave peak is considered essential.

Hertz (Hz) - Unit of frequency representing one cycle per second of alternating current.

High voltage (HV) - Voltage exceeding 1,000 volts AC or 1,500 volts DC between conductors (L-L or L-N), or 600 volts AC or 900 volts DC between conductors and earth (L-G, N-G).

HV - Abbreviation for high voltage

Hybrid generator - Alternative name for combination wave generator

Hz - Abbreviation for Hertz

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I

IEC - Abbreviation for International Electrotechnical Committee

IEEE - Abbreviation for The (American) Institutes of Electrical and Electronics Engineers. Many IEEE publications have been adopted as American National Standards

IEEE 587-1980 - A technical standard originally published in 1981 by the Institute of Electrical and Electronic Engineers (IEEE). It was superseded by IEEE C62.41 -1991 and is recognized as an American National Standard.

Impedance - A measure of the response of an electric circuit to an alternating current. In addition to the resistance, the current is also opposed by the capacitance and inductance of the circuit. Impedance is this combined oppositions to current flow.

In-line or series - Component of device installed within a voltage is generated by a change in the current, either in the circuit itself (self-inductance) or in a neighboring circuit (mutual inductance).

Inductance - The property of an electrical component, which opposes the flow of electric current. An inductor has the property of impedance, the opposition to the flow of electric current.

Inductive coupling - A magnetic field transformer between lightning and cables

Interwinding capacitance - Capacitance existing between two wound or coiled wires, such as those found in a transformer.

I/O - Abbreviation for input/output. The term is used to refer to those operations, devices and data-bearing media that are used to pass information into or out of a computer.

Isolation - To cut off the power supply to an installation , or a separate part of it, so that it can safely be worked upon.

Isolator - A mechanical switching device for the purpose of isolation

ITU-T (formerly CCITT): The ITU Telecommunication Standardization Sector (ITU-T) coordinates standards for telecommunications on behalf of the International Telecommunication Union (ITU) and is based in Geneva, Switzerland. Prior to 1992, it was known as the International Telegraph and Telephone Consultative Committee (CCITT, from the French name "Comité consultatif international téléphonique et télégraphique").

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J

Joule (J) - Measure of energy contained in an impulse or conversely it is a measure of the absorption capability of a surge protection device. 1 joule = 1 watt x 1 second.

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K

K - Abbreviation for kilo (meaning thousand) used as a prefix to units of voltage (V), current (A), energy (J), etc.

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L

L-L - Abbreviation for line-to-line

L-G - Abbreviation for line-to-ground

L-N - Abbreviation for line-to-neutral

LAN - Abbreviation for local area network

LED - Abbreviation for light emitting diode

LEMP - Abbreviation for lightning electromagnetic pulse

Let-through voltage - The part of a transient overvoltage that is allowed through a protector. It is important to remember that the let-through voltage is the sum of the voltage drop across the surge protector itself plus the voltage drops that appear across the wiring that connects the protector to the power lines. The protector clamping voltage is only one part of the let-through voltage and frequently is of secondary importance to the wiring drop.

Lightning electromagnetic pulse (LEMP) - A disturbance produced by the electromagnetic field caused by a lightning discharge and resulting in transient overvoltages.

LPS - Abbreviation for lightning protection system

Lightning protection system (LPS) - The whole system of lightning conductors and earth connections used to protect a building or structure from the effects of a direct lightning strike.

Live - A conductor or circuit which is not at earth potential and is therefore carrying a voltage

Load - Equipment or devices drawing power from a power source. Also the output side of a power source.

Local area network (LAN) - A communication system that links many computers, printer, data storage devices, and the like, together within a building or plant (e.g.. Ethernet).

Longitudinal - The voltage that appears between each of two or more conductors and earth. See common mode.

Low voltage (LV) - Voltage not exceeding 1,000 AC or 1,500 DC between conductors (L-L or L-N), or 600 volts AC or 900 volts DC between conductors and earth (L-G or N-G).

LV - Abbreviation for low voltage

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M

M - Abbreviation for meter. Also abbreviation for milli when used in conjunction with other units (e.g. Msec).

M - Abbreviation for mega (meaning 1,000,000 or 106), used as a prefix to units (e.g. MHz).

Magnetic field - The magnetic field of force surrounding a current-carrying conductor.

Maximum operating voltage - Maximum allowable continuous sinusoidal voltage (RMS) at 50-60 Hz. If suppressor is exposed to a continuous voltage higher than RMS voltage stated in specification, the suppressor may suffer damage.

MCB - Abbreviation for main circuit breaker

MCCB - Abbreviation for molded case circuit breaker

Measured Limiting Voltage - The maximum magnitude of voltage that is measured across the terminals of the SPD during the application of impulses of specified wave shape and amplitude.

Meshed earthing system - A system of earth electrodes or earth conducts that has been interconnected so as to form a grid or mesh or interconnections.

Metal cladding - The metal outer layer or skin used in the construction of many industrial buildings.

Metallic - See differential mode

Metal Oxide Varistor (MOV) - A type of suppression component. In standby mode, the MOV presents a very high resistance in shunt with the power line, drawing negligible current. When an incoming transient exceeds a critical voltage threshold, the MOV switches rapidly to a near "short-circuit" diverting mode, handling thousands of transient amperes. When the transient surge expires, the MOV components reset instantly to the reset mode, ready to respond to future transients.

Micro - A prefix to units of measurement meaning one millionth or 10-6. It is symbolized by the Greek letter � (e.g. �sec).

Milli (M) - A prefix to units of measurement meaning one thousandth or 10-3 (e.g. Mm or ms).

Mode - Synonym for transmission mode. With regard to transient overvoltages the term is used to describe the pair or pairs of conductors that transient overvoltages exist between.

Modes of protection - Refers to the presence of surge suppression components connected between phases to neutral, phases to ground, neutral to ground, and between phases. (See common mode and normal mode).

Moisture barrier - Outer layer of, most typically, a data communication cable designed to protect its conductors from moisture.

Mutual inductance - See inductance

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N

N - Abbreviation for nano

Nano (N) - Prefix to unit of measure meaning 10-9

NEMP - Abbreviation for nuclear electromagnetic pulse

Neutral - Having neither positive nor negative electric charge. The neutral wire is generally bonded to earth ground at a building service entrance, but unlike the ground wire, the neutral wire also carries load current.

Noise - A signal frequency that may be riding on top of the power line sine wave. A number of systems use the power lines to carry signals and data to other locations. Attempts to filter out the "noise" may disrupt the current or future operation of these systems. Although it is seldom needed, it is wiser to provide line conditioning filtering immediately in front of sensitive equipment.

Normal mode voltage - Voltage appearing between the phase wires and neutral of the power system wiring.

NRTL - Abbreviation for Nationally Recognized Test Laboratory, one example of which is the Underwriter's Laboratories, Inc. (UL).

Nuclear electromagnetic pulse (NEMP) - Pulses of energy caused by nuclear explosions and intense solar activity. NEMP transients are much quicker (a faster rise time) than commonly occurring transients. Also called electromagnetic pulse (EMP).

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O

Outage - A total break in the supply lasting from several milliseconds to many hours. Also referred to as a blackout or power cut.

Overvoltage - Sustained increases in the supply voltage, lasting more than a few seconds.

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P

Power Cut - A total break in the supply lasting from several milliseconds to many hours. Also referred to as a blackout or outage.

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Q

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R

RCD - Abbreviation for residual current device

Reactance - The result of the presence of capacitance and inductance

Reflection coefficient - Measure of the impedance change at a point in a cable. It is the ration of the signal reflected back from a point to the signal going into that point. High reflection coefficients can, on a data transmission systems, result in reflections which can be misinterpreted as data or data collisions, disrupting data transmission.

Repeaters - A form of booster or amplifier used at regular intervals along a transmission channel to regenerate message signals and to overcome impairments such as impedance.

Residual current device (RCD) - Device designed to disconnect a circuit if the earth leakage current exceeds a prescribed limit, typically 30 milliamps. Also know as an earth leakage circuit breaker.

Residual (transient) voltage - Alternative term for let-through voltage.

Resistance - the tendency of a material to resist the passage of an electric current and to convert electrical energy into heat energy. Resistance is measured in ohms.

Resistive coupling - This is the most common cause of transient overvoltages and it will affect both underground and overhead lines. Resistively coupled transients occur when a lightning strike raises the electrical potential of one or more of a group of electrically interconnected buildings (or structures).

Resistivity - A measure of the amount of resistance due to a material and independent of the dimensions of a sample of the material. Resistivity is symbolized by the Greek letter ρ.

Resonance - The maintenance of oscillation with minimum driving signal

Response time - The time it takes a surge protection device to switch from its "off" condition to an "on" or diverting mode. This occurs when an incoming surge voltage exceeds the clamping threshold level of the MOV or other suppression component. Organizations such as IEEE, NEMA, and Underwriter's Laboratories consider response time to be a non-issue since MOVs, SADs (and the surge protectors that use them) have response times that are 100 to 1000 times faster than any transient that they are likely to encounter.

RF - Abbreviation for radio frequency

RFI - Abbreviation for radio frequency interference

Ring main - The way in which wall sockets are supplied in the UK. The power supply is arranged in the form of a ring and is connected to a single point at the power distribution board.

RMS - Abbreviation for root mean square. It is used to find the DC heat equivalent of an AC voltage or current. For a sine wave the RMS value is equal to its peak value divided by square root of 2.

RS 232 - An internationally agreed standard for serial data transmission, specifying high and low voltage levels, timing and control.

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S

S - Abbreviation for second(s)

Sag - A momentary reduction in the voltage for a duration from a half-cycle to a few seconds. Also referred to as a dip.

Screen - To surround or encase a circuit with metal in order to reduce the effect of electric or magnetic fields. A screened cable is one which incorporates an outer layer of an earthed metal skin. To be effective for transient overvoltage protection purposes, the screen must be a good conductor and earthed at both ends.

Self-inductance - See inductance

Semiconductor - Name applied to a group of materials whose ability to conduct electric charge is greater than that of an insulator, but less than that of a conductor. Semiconductors are used in a wide variety of solid state components (such as transistors, integrated circuits, and diodes) and hence in most electronic systems. Where a semiconductor is connected to metal or to another semiconductor of different conductivity, a junction is formed. A junction is forward biased when current is flowing through it and reverse biased when it is blocking the flow of current. Bias therefore refers to the direction of the applied voltage.

Shield - See screen

Short circuit - A deliberate or (more usually) accidental low resistance connection, on an electrical circuit. Its effect is to equal voltages at two points and allow current to flow. If the short circuit is the result of a fault, it will usually cause problems.

Shunt - Alternative term for parallel

Sine wave - The natural waveform of voltage generated by a coil of wire revolving in a uniform magnetic field. It is therefore the waveform an AC main power supply approximate to.

Single phase - Power supply incorporating one live conductor. See phase

Spike - Alternative term for transient overvoltage

Star supply - Three phase power supply incorporating a neutral conductor

Suppression level - Voltage at which transient overvoltages are controlled or suppressed

Surge - Common, but ambiguous alternative for transient overvoltages

Switchfuse - Fuse incorporating a switch or isolator, thereby enabling the power supply to devices fed from it to be turned off.

Switching transient - Transient overvoltage caused by the operation of large inductive or capacitive loads.

Symmetrical mode - See differential mode

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T

Telemetry - The measurement of events at a distance. Transducers are used to measure physical activities and to convert these to signals that reflect the measurement of phenomena. The signals are transmitted, often over telephone lines, to a data collection center for processing. As a result of which, signals may be transmitted back to the distance location to control the process being monitored.

Three phase - Power supply incorporating three live conductors

Transceiver - A device used in data communication networks that can transmit and receive information

Transformer - A general term describing a component or device that magnetically transforms one alternating voltage to another without change of frequency. The usual construction is based upon two or more coils (or windings) of wire placed close to each other. The voltage change is proportional to the difference in the number of turns or windings between each coil.

Transient Control Level (TCL) - Term used in BS 6651:1992 to describe the portion of the transient overvoltage reaching equipment. This must be lower than the equipment transients design level or susceptibility level. In essence, transient control level means the same as let-through voltage.

Transient overvoltage - An increase in voltage between two or more conductors, lasting from microseconds to a few milliseconds in duration.

Transverse mode - See differential mode

Trunking - A square or rectangular surround, with removable cover, for mechanically protecting cables

Twisted pair - A cable consisting of a pair of conductors twisted around each other, in order to reduce interference. This is a simple and common communication medium widely used in telephony and other low-frequency applications.

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U

UL - Abbreviation for the American Underwriters Laboratory, a testing and approvals body

Undervoltage - A decrease in the normal voltage level lasting for seconds or minutes. Also referred to as a brownout.

Uninterruptible power supply (UPS) - Contains batteries that store energy, which provides a power source during power interruptions.

Utility - A company that performs and essential utilitarian service, like providing natural gas and electricity for people.

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V

VAC - Volts of alternating current

Varistor - A semiconductor device whose resistance varies with the applied voltage

Volt (V) - The unit of voltage or potential difference

Voltage - Electrical pressure, or electromotive force (EMF). The force that causes current to flow through a conductor, expressed as a difference of potential between two points, since it is a relational term. Connecting both voltmeter leads to the same point will show no voltage present, although the voltage between that point and ground may equal hundreds or thousands of volts. Thus, most nominal voltage are expressed as phase to phase or phase to neutral. The unit of measurement is volts and the electrical symbol is V.

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W

Watt (power) - The unit of power that equals 1 joule per second and measures how much electricity an appliance needs to operate satisfactorily. An electrical unit of power often used to rate appliances using relatively small amounts of electricity. Wattage is stamped on light bulbs and all appliances. The mathematical relationship between watts, volts, and amperes is wattage = ampere x voltage. For example a 120 V, 20 A circuit will carry 2400 watts.

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