Glossary

A

ac – See alternating current

ac filter – A power electronic device that eliminates harmonics, attenuates distortions and/or EMI/RFI noise.

Available interrupt current (AIC) – The highest current at rated voltage that a device is intended to interrupt under standard test conditions.

Alternating current (ac) – Electrical current which reverses direction periodically, expressed in hertz or cycles per second. Abbreviated “ac”. The number of such cycles per second equals the frequency in hertz, i.e. 60 cycles per second = 60 hertz (Hz), in the United States.

Ampere – The quantitative unit measurement of electrical current.

Ampacity -A term used to describe current-carrying capacity, expressed in amperes, of a wire or cable.

Amperage – The strength of an electric current measured in amperes.

Amplifier -A device used to increase the power and voltage level of a signal.

Arrester -See surge arrester.

ATS – See autotransfer switch

Attenuation – The reduction of a signal or electrical surge from one point to another. Wire resistance, surge protective devices (SPDs) , high voltage arresters, and power conditioners attenuate surges to varying degrees.

Attenuator- A passive device used to reduce signal strength.

Autotransfer switch (ATS) – A device that automatically transfers power from one source to another.

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B

Back Filter – A filter inserted in the power line feeding an equipment to be surge tested; this filter has a dual purpose: (1) To prevent the applied surge from being fed back to the power source where it may (might according to the word usage in this guide) cause damage. (2) To eliminate loading effects of the power source on the surge generator. (IEEE 100)

Balanced load – An alternating current (ac) power system that has more than two current-carrying conductors that carry equal, i.e., balanced, currents.

Bonding – A complete and permanent electrical interconnection between two or more points (usually grounding systems) that reduces any voltage difference.

Branch circuit – An electrical circuit individually protected by a fuse or circuit breaker that starts at the service panel and ends at the electrical outlets.

Breaker – Short for circuit breaker.

Brownout — A long-duration under-voltage condition, usually hours or days in length. Brownouts can be caused by heavy usage during peak hours, or they may be planned as an energy conservation strategy.

Building service entry - The point where commercial power enters the building.

Bus bar (bus) – A heavy, rigid conductor that serves as a common connection for two or more circuits.

Bypass – A circuit that provides an alternative path for electrical power to go around (or bypass) its normal path and allows maintenance personnel to service equipment, like UPSs, without interrupting service.

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C

Capacitance – A term referring to the electrical properties of a capacitor or to a circuit that displays capacitor-like behavior.

Capacitor – A discrete electrical device which has two electrodes and an intervening insulator, which is called the dielectric.

Capacity – The rated load of a machine, apparatus, or appliance. Maximum capacity is the maximum load of a machine, apparatus, or appliance of which it is capable under existing service conditions.

Category A, B, C - Categories of location for transient suppression within a
facility. Class A refers to outlets and long branch circuits. Class B refers to major feeders and short branch circuits near the distribution panel. Class C refers to the commercial power service entrance and outside the facility (refer to IEEE C62.41).

CATV
(Community Antenna Television) – An RF distribution system which distributes television broadcast programs, original programs, premium programming and other services using a network of coaxial cable.

CBEMA – The former Computer and Business Equipment Manufacturers Association; replaced by the Information Technology Industry Council (ITIC).

CBEMA curve – A set of curves developed by the Computer Business Equipment Manufacturers Association (CBEMA) that represents the withstand capabilities of computers in terms of the magnitude and duration of a voltage disturbance.It was a standard for measuring the performance of all types of equipment and power systems until replaced by the Information Technology Industry Council (ITIC) curve.

Choke – A form of inductor which is constructed to allow desirable frequency signals to pass while acting with high impedance to other signals at some undesirable frequency.

Circuit breaker – A resettable device that responds to a preset level of excess current flow by opening the circuit, thereby preventing damage to circuit elements.

Clamping voltage – The peak voltage that SPDs allow into an electric circuit based on a specific test waveform. See Measured Limiting Voltage

Coax - A cable constructed by using two concentric conductors separated by an insulator.

Coaxial cable- A popular transmission medium usually consisting of one central wire (two for twinaxial) surrounded by a delicate insulator and encased in either a wire mesh or an extruded metal sheathing. Also, a concentric cable consisting of a center conductor, a dielectric, and a shield. Coax used for most MATV and CATV work has a characteristic impedance of 75 ohms.

Common mode (CM) – Refers to electrical interference measured as a ground reference signal common to both of two current-carrying conductors.

Common mode noise (voltage) - Electrical noise between the power conductors and ground, i.e., between line and ground or between neutral and ground.

Composite video signal – the complete video signal including the picture (luminance) signal, the blanking and sync pulses, and the color (chrominance).

Conductor – An object or substance, usually a wire, bus bar, rod, or tube, that conducts, i.e., provides a path for, electric current.

Conduit – A tube, duct, or pipe that provides a metallic or nonmetallic tubular raceway for wires and cables that carry data or power.

Cord connected Type 3 Point of utilization SPDs, installed at a minimum conductor length of 10 meters (30 feet) from the electrical service panel to the point of utilization, for example cord connected, direct plug-in, receptacle type and SPDs installed at the utilization equipment being protected. The distance (10 meters) is exclusive of conductors provided with or used to attach SPDs.

Coupling – The means by which power or signals transfer from one circuit element or network to another. Also, the effect of a power or signal source interfering with a signal transmission system.

CPU – An acronym used for the central processing unit of a computer.

Critical load- That portion of electrical/electronic equipment for which power quality is a vital consideration. The term “load” applies to all current-carrying devices on a given circuit or feeder. The term “critical load” refines the language to include only those current-using devices whose operation is considered essential.

Cross talk – The unwanted transfer of energy from one communication circuit to another by means of mutual inductive, capacitive, or conductive coupling.

Crowbar – A circuit that protects sensitive equipment by becoming a “crowbar” (or short circuit) between power conductors when conditions require it and temporarily shunting all current to ground and clamping the voltage
to zero.

CSA – The abbreviation for Canadian Standards Association, a Nationally Recognized Testing Laboratory headquartered in Canada.

Current – The flow of electricity in a circuit as expressed in amperes.Current refers to the quantity or intensity of electrical flow. Voltage, on the other hand, refers to the pressure or force causing the electrical flow.

Current balance – The equal flow of current in each phase of a three-phase power system.

Current carrying – A circuit component carrying current.

Current distortion – Distortion in the ac waveform.See distortion.

Current transformer (CT) – A device that provides a means for measuring current beyond the range of a meter and uses the strength of the field around the conductor to induce a current in its secondary.

Cutout – A device used manually or automatically to interrupt current through any particular apparatus or equipment.

Cycles per second – A term that describes the frequency of alternating current (ac).Frequency is more properly described using the term “hertz“, which is synonymous with cycles per second.

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D

dB - See decibel

dc - See direct current

dc standby current (varistor) – Varistor current measured at rated dc voltage (IEEE 100).

Decibel (dB) – A logarithmic function used to simplify MATV calculations. Decibels may be added or subtracted. 0 dB is the standard reference level for all MATV calculations.

Delta – A standard three-phase circuit connection configured such that the ends of each phase winding connected in series form a closed loop with each phase 120 electrical degrees from the other. It appears as a triangle and looks like the Greek letter delta (r).

Delta connection – A method of connecting a three-phase source or load in series to provide a closed circuit (three-wire, plus ground).

Delta-delta – Three-phase transformer circuit created by a delta source and a delta load with both the primary and secondary winding connected in a delta configuration.

Delta-wye – Three-phase transformer circuit created by a delta source and a wye load with the transformer primary connected in a delta configuration and the transformer secondary connected in a wye configuration.

Demand (kW) – The maximum electrical power, in fifteen minute intervals, that a utility customer requires from the utility.

Derating factor – A factor in percent for reducing the capacity of electrical equipment, like transformers.

Differential-mode voltage – The voltage (noise) that appears across two specified sets of active conductors. See transverse mode noise.

Device failure – An irreversible change in characteristic, resulting in an inability to perform as intended. (SC definition)

Digital multimeter (DMM) – An instrument that measures voltage, current, and resistance and displays measurements on a digital readout.

Diode – A two-terminal device that conducts current better in one direction that the other. It uses include rectification (ac to dc conversion) and detection (retrieving an information signal from a modulated carrier wave).

Diode/capacitor input – A power supply that uses a full-wave bridge rectifier connected to a capacitor to produce a pulse current.

Direct coupling – Two circuits connected to each other through an inductor resistor, or wire.

Direct current (dc) – A unidirectional current whose average value does not equal zero but a constant number.

Direct plug-in – Any SPD incorporating integral blades for direct insertion into a standard wall receptacle. (UL 1449-1996*).

Disk – A memory device which uses a magnetic media for the storage of information. Disk, as a term, has expanded into other areas often used to describe the shape of the storage media, that is: floppy disk, compact disk, laser disk, or hard disk. It sometimes refers to the way in which the storage media mimics a disk media; that is, RAM disk or bubble memory.

Distortion – The wave shape of a signal that is not normal is distorted. Distortion is a term that describes abnormal wave shapes.

Distortion factor – The ratio of the root means square(rms) of the harmonic content of a waveform to the rms of the fundamental quantity, expressed in percent of the fundamental.See total harmonic distortion (THD).

Distribution- The way in which power is routed to various current-using
sites or devices. Outside the building, distribution refers to the process of routing power from the power plant to the users. Inside the building, distribution is the process of using feeders and circuits to provide power to devices.

Disturbance – Any event that adversely affects the normal power flow in a system, such as lightning or a short circuit.

Dropout – Loss of equipment operation due to noise, sag, or interruption. A discrete voltage loss. Or a voltage sag (complete or partial) for a very short period of time (milliseconds).

Dropout voltage - The voltage at which a device fails to operate.

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E

Earth electrode – A ground electrode, water pipe, building steel, or some combination of these, that establishes a building’s earth ground.

Earth ground – A low-impedance path to earth that discharges lightning, static, and radiated energy, and keeps the main service entrance at earth potential.

Eddy currents – Induced currents in transformer winding and core caused by the magnetic field from the normal alternating current and harmonics.

Effective value – For any time-variant voltage or current waveform, the constant value that gives the same average power. For sinusoidal waveforms, the effective value equals 0.707 times the peak value.

Electric field – Describes forces associated with electrical charges.

Electrode – Generally, a conducting medium through which an electric current enters or leaves a different medium, such as an electrolyte, gas, or vacuum.

Electromagnetic – A magnetic field caused by an electric current. For example, the electric current in energized power lines causes electromagnetic fields that can interfere with nearby data cables.

Electromagnetic compatibility – The ability of a device, equipment, or system to function satisfactorily in its electromagnetic environment without introducing intolerable electromagnetic disturbances to anything in that environment.

Electromagnetic interference (EMI) – A term that describes electrically-induced noise or transients.

Electromagnetic susceptibility – The inability of a device, equipment, or system to function without degradation in the presence of an electromagnetic disturbance.

Electrostatic discharge (ESD) – The effects of static discharge can range from simple skin irritation for an individual to degraded or destroyed semiconductor junctions for an electronic device.

EMF – Electromotive force, or voltage.

EMI – See electromagnetic interference

EMP Electromagnetic pulse.

Energy – The capability of doing work over time, expressed in kilowatt-hours for electrical energy.

Equipment grounding conductor – The conductor that connects the non-current-carrying parts of conduits, raceways, and equipment enclosures to the grounded conductor (neutral) and the grounding electrode at the service equipment entrance (main panel) or secondary of a separately derived system (e.g., isolation transformer).See Section 100 in ANSI/NFPA 70-1990.

ESD - See electrostatic discharge

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F

Failure Mode – The observed effects of failure.

Farad – Unit of measurement for capacitance.

Fast tripping (fuse saving) – The common utility protective relaying practice in which the circuit breaker or line recloser operates faster than a fuse can blow. It clears transient faults without a sustained interruption but subject’s industrial loads to a momentary or temporary interruption.

Fault – An unintentional short circuit that causes a failure or interruption in an electrical circuit or a power system.

Fault transient – A short circuit on the power system, usually caused by lightning, tree branches, or animals and cleared by momentarily interrupting the current.

Feeder – An electrical supply line, either overhead or underground, that connects from a generating plant or an interchange point to a load or distribution system.

FERCFederal Energy Regulatory Commission

Field effects – The effects of electric and magnetic fields on objects near current-carrying conductors.

Filter – An electronic device which opposes the passage of a certain band while allowing other frequencies to pass. Filters are designed to produce four different results. Ahigh-pass filter allows all signals above a given frequency to pass. A low-pass filter allows only frequencies below a given frequency to pass. A bandpass filter allows a given band of frequencies to pass while attenuating all others. A trap filter allows all frequencies to pass but acts as a high-impedance device to the tuned frequency of the filter.

Fixed peak current – A desired (specified) test current level which has taken into consideration the additional impedance of the specimen under test, requiring adjustment of the pre-set open-circuit voltage or short-circuit current of the surge generator. (SC definition)

Flashover – Arcing that is caused by the breakdown of insulation between two conductors where a high current flow exists, with a high potential difference between the conductors.

Fluctuation – A change, i.e., surge or sag, in voltage amplitude, often caused by load switching or fault clearing.

Follow currentCurrent supplied by the electrical power system and flowing through the SPD during and following the passage of discharge current.

Forced outage – A power system interruption caused by the improper operation of equipment or human error.

Forward transfer impedance – The amount of impedance between the source and load that affects the transfer of power, including harmonics and inrush current, to the load.

FPN – Fine print note; National Electrical Code® (NEC®) explanatory material.

Frequency – The number of times is a specific period (how frequently, usually in

cycles per second) alternating current(ac) reverses its direction, measured in hertz(Hz). Each reversal from one direction to another and back again constitutes a cycle. In North America, utilities provide power with a frequency of 60 cycles per second, or 60 hertz. In ac circuits, designates number or times per second that the current completes a full cycle in positive and negative directions. See also
alternating current.

Frequency deviation – A variation, i.e., increase or decrease, in the nominal power frequency that can occur from several cycles to several hours.

Frequency modulation (FM) – A method to change a carrier frequency so that it varies above and below a center or resting frequency in step with the signal it transmits.

Frequency response – A measurement of how well a device or circuit transmits various frequencies.

Fuse – An overcurrent protective device with a fusible link that operates and opens the circuit on an overcurrent condition.

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G

Gain – A measure of amplification of a device, usually expressed in dB and at the highest frequency of operation.

Generate – To produce electrical energy.

Generation – The act or process of converting other forms, e.g., mechanical, chemical, solar, or nuclear of energy, into electric energy.

GFI (Ground Fault Interrupter) – A device that interrupts the flow of electric current in an electric circuit when the fault current to ground exceeds some predetermined value.

Ghosting – A signal interference condition producing positive or negative pictures displaced in time from the desired picture, caused by multi-path signal reception. Ghost pictures also result from cable ringing.

Grid – An interconnected system of electric transmission lines and associated equipment that moves or transfers bulk electric energy from the generators to the loads.

Ground – A general term that refers to the point at which other portions of a circuit are referenced when making measurements. Power systems grounding is that point to which the neutral conductor, safety ground, and building ground are connected. This grounding electrode may be a water pipe, driven ground rod, or the steel frame of the building.

Ground block – Connector which passes the RF signal through with minimum loss while providing a means of attaching a ground wire to the drop cable typically near the entry to the home. Grounding is accomplished by either a special ground rod or connection to the water system (See your local code for required grounding methods)

Ground electrode – A conductor or group of conductors in contact with the earth that provides a low-impedance connection to the ground.

Ground fault – Any undesirable current path from a current-carrying conductor to ground.

Ground grid – A system of interconnected bare conductors arranged in a pattern over a specified area, on a buried below the surface of the earth, that provides safety for workers by limiting potential differences within it perimeter to safe levels. It does not act as a signal reference grid.

Ground impedance tester – An instrument that measures the impedance of a circuit from the point of test to the bond between the neutral and ground bond. Some can handle 120 V ac single-phase voltage while others can handle 600 V ac three-phase voltage. It also measures voltage and determines the presence of neutral-to-ground connections, isolated ground shorts, reversed polarity, and an open equipment grounding conductor.

Ground loop - The condition of having two or more ground references in a common system. When two or more grounds have a potential difference between them, current can flow. This flow of current is a new circuit or loop which can interfere with the normal operation of the system.

Ground noise – An undefined, imprecise term that describes unwanted electrical signals appearing between the earth conductor and any other conductor.

Ground potential rise (GPR) – When a large amount of energy is rapidly deposited into the ground by a cloud-to-ground lightning strike or by an electrical fault on a utility power system, the ground potential at this injection point rises to a higher level with respect to the more distant ground. This has the effect of creating a voltage potential gradient in the earth, which can cause dangerous touch and step potentials to personnel exist. By creating an equi-potential ground plane beneath a facility by electrically bonding all separate “grounds” into a “system” or by burying ground mats and meshes, this danger to personnel and equipment can be reduced. It is also important to note that GPR is not only dangerous to personnel, it can also cause damage to equipment.

Ground window – The opening through which all grounding conductors, including metallic raceways, enter a specific area.Provides the building grounding system a connection to an area that would otherwise have a grounding connection.

Grounded – Connected to earth or to some conducting body that substitutes for earth.

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H

Hard-wired – Applied to equipment that connects its power source with wiring (generally customer or contractor-supplied) attached directly to terminal blocks or distribution panels rather than via an input line cord and output receptacle.

Harmonic – A frequency that is a multiple of the fundamental frequency.For example, 120 Hz is the second harmonic of 60 Hz, 180 Hz is the third harmonic, and so forth.

Harmonic content – The waveform that remains after subtracting the fundamental component from a harmonic waveform.

Harmonic distortion - Excessive harmonic content that distorts the normal sinusoidal waveform is harmonic distortion. This can cause overheating of
circuit elements and might appear to a device as data-corrupting noise.

Harmonic resonance – The power quality term that describes the condition that sometimes occurs in electrical systems in which high currents flow through and damage capacitors or clear fuses in connecting circuits. A condition in which the power system resonates at one of the major harmonics produced by nonlinear elements in the system and increases the harmonic distortion.

Henry – Unit of measurement for inductance.

Hertz – A term describing the frequency of alternating current. The term hertz is synonymous with cycles per second. Abbreviated Hz.

High-pass filter – A filter that passes all frequencies above a certain level, and stops all lower frequencies.

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I

IEC  – The International Electrotechnical Commission (IEC) is an international standards-setting body for electrical and electronic technologies.

IEEE - The Institute of
Electrical and Electronic Engineers
(IEEE) is an international society of engineers that develops its own standards.

Impedance – Measured in ohms, impedance is the total opposition to current flow in a circuit where alternating current is flowing. This includes inductive reactance, capacitive reactance, and resistance. Symbol is Z.

Impulse -A surge of unidirectional polarity. Ref: IEEE.

Impulsive transient – A sudden non-power frequency change in the steady-state condition of voltage or current that occurs in unidirectional polarity (primarily either positive or negative.)

Inductance- This term describes the electrical properties of a conductor and its resultant magnetic field when an alternating current is passed through it. This interaction offers an impedance to current flow, thereby causing the current waveform to lag behind the voltage waveform. This results in what is known as a lagging power factor.

Inductor -A discrete circuit element which has the property of inductance. It should be noted that at very high radio frequencies, a straight wire or a path on a printed-circuit board can act as an inductor.

Inductive reactance – The impedance to alternating current produced by inductors.

Insertion loss – Also called “feed through loss”. This is the loss that occurs as signals pass through a passive device. Insertion loss occurs in all devices which do not amplify the signal.

Input line cord – The power cord connected to the input terminals of the uninterruptible power supply (UPS) that plugs into an ac utility outlet to supply power to the UPS.

Inrush current – The initial large current demand needed to start up certain types of electrical equipment, like motors, before their resistance or impedance increases to their normal operating value.

Instantaneous – A qualifying term applied to a circuit breaker or other device indicating that no delay is purposely introduced into its action.

Insulation (electrical) – A dielectric substance or air space permanently offering a high resistance to the passage of current and to disruptive discharge through the substance or space. For example, a  non-electrical-conducting material, like rubber or polyethylene, is used to resist current flow.

Insulation (thermal) – A non-heat-conducting material, like fiberglass, that resists heat flow and provides a barrier to heat loss.

Insulator - A device made of porcelain, glass, rubber, or wood that prevents current from flowing, like a porcelain support that insulates conductors from a pole or tower.

Isolation – The degree to which a device can separate the electrical environment of its input from its output, while allowing the desired transmission to pass across the separation.

Interconnection system – A connection between two electrical systems that allows the transfer of electric energy in either direction.

Internal impedance – The inherent impedance inside a device or circuit.

Interruptible power – Power that the supplier and the customer have agreed can be stopped by the supplier.

Interruption, sustained (power quality) – The complete loss of voltage (<0.1 pu) on one of more phase conductors for a long time period greater than 1 minute.

Inverter – An inverter converts dc power into ac power.

Isolated ground – An insulated equipment grounding conductor that runs in the same conduit or raceway as the supply conductors and is insulated from the metallic raceway and all ground points throughout its length. It originates at an isolated ground-type receptacle or equipment input terminal block and terminates at the point where neutral and ground bond at the power source. See NFPA 70-1990, Section 250-74, Exception 4, and Section 250-75, Exception.

Isolation – Separation between electrical input and output, such as an isolation transformer or optical coupler or separation of one section of a system from the undesired influences of other sections.

Isolation transformer - A multiple-winding transformer with physically separate primary and secondary windings that allows the magnetic field in the winding of the primary to create (induce) electrical power in the secondary winding but minimizes electrostatic transfer to the secondary windings. This way the electrical power available at the input transfers to the output, but some of the unwanted electrical effects in the input power do not reach the transformer’s output.

ITIC (Information Technology Industry Council) - replaced the former Computer Business Equipment Manufacturers Association.

ITIC Curve - Replaces the former CBMA curve and provides a set of curves developed by the Information Technology Industry Council (ITIC) that represents the withstand capabilities of computers in terms of the magnitude and duration of the voltage disturbance.

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J

Joule – The surge energy (watt seconds) that the device is capable of absorbing.

Jumper – A short length of conductor that connects two points in a circuit.

Junction box (J box) – A box with a blank cover that provides space to connect and branch enclosed conductors.

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K

k-rated transformer – A transformer specially designed to handle harmonics.

Kilovolt-Ampere (kVA)- An electrical unit related to the power rating of a piece of equipment. It is calculated by multiplying the rated voltage of equipment by the current required (or produced).For resistive loads 1 kilovolt-ampere equals 1 kilowatt.

Kilohertz (kHz) – A term meaning 1000 cycles per second.

Kilowatt (kW) – The product of the root-mean-square (RMS) current, the root-mean-square (RMS) voltage, and the power factor divided by 1000.

Kilowatt-hour (kWh) – The basic unit of electric energy that equals 1000 watts of power used for 1 hour. The amount of power the customer uses is measured in kilowatt-hours (kWh).A measurement of power and time used by utilities for billing purposes.For example, a 75-watt light bulb that burns for 10 hours consumes 0.75 kWh (75 watts x 10 hours) or 750 watt-hours.

Kirchhoff’s laws of electric networks – The sum of the electrical currents flowing to a point in a network equals the sum of the currents flowing away from that point.

KVA (1000 VA) – The product of the root-mean-square (RMS) current and the root-mean-square (RMS) voltage divided by 1000; provides the actual measured apparent power and is used for circuit sizing.

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L

Lag – The time delay between two events (usually electrical quantities), such as delay of current behind voltage.

Lagging load – An inductive load that resists changes in current in which current lags voltage. The time lag between current and voltage is measured in electrical degrees and is known as the phase angle. The cosine of this angle equals the power factor (linear loads only).

LAN (Local Area Network) – A data communications system confined to a certain area. The area served may consist of a single building, or a cluster of buildings.

LC circuit – An electric network that contains both inductive and capacitive elements.

Leading load – A capacitive load that resists changes in voltage with current leading the voltage.

Leakage current – Any current, including capacitively coupled currents, that may be conveyed from accessible parts of a product to ground or to other accessible parts of the product. (UL 1449)

Leased line – A dedicated circuit, typically supplied by the telephone company, that permanently connects two or more user locations. These lines are used to transmit data.  See T1.

LED (light emitting diode) – A semiconductor that emits light when current passes through it.

Lifetime rated pulse currents (varistor) – Derated values of Itm for impulse duration’s exceeding that of an 8/20 us wave shape, and for multiple pulses which may be applied over device’s rated lifetime. (IEEE 100)

Lightning arrester – See surge arrester.

Line - A designation of one or more power-carrying conductors for power distribution. The black (or red or blue) wire is the line conductor, the white wire is the neutral, and the green wire is ground. The voltage difference between the line conductor and the neutral is the supply voltage, i.e., 120 volts.

Line conditioner - A line conditioner contains multiple protection devices in one package to provide, for example, electrical noise isolation and voltage regulation.

Line filter – A filter in series with a transmission line that removes unwanted electrical signals.

Line imbalance – Unequal loads on the phase lines of a multiphase feeder.

Line loss – The heat loss in a line caused by the flow of the current through the resistance in the line, usually called I2R loss.

Line to Line
(L-L) – A term used to describe a given condition between conductors of a multiphase feeder.

For normal mode protection, the SPD should provide protection between each current carrying conductor pair (L–L and L–N).For common mode protection, the SPD should provide protection between the line-to-ground (L–G) and/or neutral-to-ground (N–G) modes.

Line to Neutral (L-N) – A term used to describe a given condition between a phase conductor and a neutral conductor.

For normal mode protection, the SPD should provide protection between each current carrying conductor pair (L–L and L–N).For common mode protection, the SPD should provide protection between the line-to-ground (L–G) and/or neutral-to-ground (N–G) modes.

Linear load – An electrical load device, which, in steady-state operation, provides an essentially constant load impedance to the power source throughout the applied voltage cycle and in which the current relationship to voltage remains constant for a relatively constant load impedance.

Load – Any electrical device connected to a power source may be called by the general term of “load”.

Load balancing – Switching the various loads on a multiphase feeder to equalize the current in each line.

Load fault – A malfunction, like a tree touching a power line, that causes the lead to demand abnormally high amounts of current from the source.

Load unbalance – Unequal loads on the phase lines of a multiphase system.

Loss – The power dissipated in a power system circuit expressed in watts. In communications, the ratio of the signal power delivered by a device under ideal conditions to the signal actually delivered expressed in decibels (dB).

Low-pass filter – A filter that passes all frequencies below a certain designated cutoff point and blocks all frequencies above that point.

 

*(Note: UL 1449 Third Edition went into effect September 2009. Updates pending.)

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A

ac – See alternating current

ac filter – A power electronic device that eliminates harmonics, attenuates distortions and/or EMI/RFI noise.

Available interrupt current (AIC) – The highest current at rated voltage that a device is intended to interrupt under standard test conditions.

Alternating current (ac) – Electrical current which reverses direction periodically, expressed in hertz or cycles per second. Abbreviated “ac”. The number of such cycles per second equals the frequency in hertz, i.e. 60 cycles per second = 60 hertz (Hz), in the United States.

Ampere – The quantitative unit measurement of electrical current.

Ampacity -A term used to describe current-carrying capacity, expressed in amperes, of a wire or cable.

Amperage – The strength of an electric current measured in amperes.

Amplifier -A device used to increase the power and voltage level of a signal.

Arrester -See surge arrester.

ATS – See autotransfer switch

Attenuation – The reduction of a signal or electrical surge from one point to another. Wire resistance, surge protective devices (SPDs) , high voltage arresters, and power conditioners attenuate surges to varying degrees.

Attenuator- A passive device used to reduce signal strength.

Autotransfer switch (ATS) – A device that automatically transfers power from one source to another.

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B

Back Filter – A filter inserted in the power line feeding an equipment to be surge tested; this filter has a dual purpose: (1) To prevent the applied surge from being fed back to the power source where it may (might according to the word usage in this guide) cause damage. (2) To eliminate loading effects of the power source on the surge generator. (IEEE 100)

Balanced load – An alternating current (ac) power system that has more than two current-carrying conductors that carry equal, i.e., balanced, currents.

Bonding – A complete and permanent electrical interconnection between two or more points (usually grounding systems) that reduces any voltage difference.

Branch circuit – An electrical circuit individually protected by a fuse or circuit breaker that starts at the service panel and ends at the electrical outlets.

Breaker – Short for circuit breaker.

Brownout — A long-duration under-voltage condition, usually hours or days in length. Brownouts can be caused by heavy usage during peak hours, or they may be planned as an energy conservation strategy.

Building service entry - The point where commercial power enters the building.

Bus bar (bus) – A heavy, rigid conductor that serves as a common connection for two or more circuits.

Bypass – A circuit that provides an alternative path for electrical power to go around (or bypass) its normal path and allows maintenance personnel to service equipment, like UPSs, without interrupting service.

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C

Capacitance – A term referring to the electrical properties of a capacitor or to a circuit that displays capacitor-like behavior.

Capacitor – A discrete electrical device which has two electrodes and an intervening insulator, which is called the dielectric.

Capacity – The rated load of a machine, apparatus, or appliance. Maximum capacity is the maximum load of a machine, apparatus, or appliance of which it is capable under existing service conditions.

Category A, B, C - Categories of location for transient suppression within a
facility. Class A refers to outlets and long branch circuits. Class B refers to major feeders and short branch circuits near the distribution panel. Class C refers to the commercial power service entrance and outside the facility (refer to IEEE C62.41).

CATV
(Community Antenna Television) – An RF distribution system which distributes television broadcast programs, original programs, premium programming and other services using a network of coaxial cable.

CBEMA – The former Computer and Business Equipment Manufacturers Association; replaced by the Information Technology Industry Council (ITIC).

CBEMA curve – A set of curves developed by the Computer Business Equipment Manufacturers Association (CBEMA) that represents the withstand capabilities of computers in terms of the magnitude and duration of a voltage disturbance.It was a standard for measuring the performance of all types of equipment and power systems until replaced by the Information Technology Industry Council (ITIC) curve.

Choke – A form of inductor which is constructed to allow desirable frequency signals to pass while acting with high impedance to other signals at some undesirable frequency.

Circuit breaker – A resettable device that responds to a preset level of excess current flow by opening the circuit, thereby preventing damage to circuit elements.

Clamping voltage – The peak voltage that SPDs allow into an electric circuit based on a specific test waveform. See Measured Limiting Voltage

Coax - A cable constructed by using two concentric conductors separated by an insulator.

Coaxial cable- A popular transmission medium usually consisting of one central wire (two for twinaxial) surrounded by a delicate insulator and encased in either a wire mesh or an extruded metal sheathing. Also, a concentric cable consisting of a center conductor, a dielectric, and a shield. Coax used for most MATV and CATV work has a characteristic impedance of 75 ohms.

Common mode (CM) – Refers to electrical interference measured as a ground reference signal common to both of two current-carrying conductors.

Common mode noise (voltage) - Electrical noise between the power conductors and ground, i.e., between line and ground or between neutral and ground.

Composite video signal – the complete video signal including the picture (luminance) signal, the blanking and sync pulses, and the color (chrominance).

Conductor – An object or substance, usually a wire, bus bar, rod, or tube, that conducts, i.e., provides a path for, electric current.

Conduit – A tube, duct, or pipe that provides a metallic or nonmetallic tubular raceway for wires and cables that carry data or power.

Cord connected Type 3 Point of utilization SPDs, installed at a minimum conductor length of 10 meters (30 feet) from the electrical service panel to the point of utilization, for example cord connected, direct plug-in, receptacle type and SPDs installed at the utilization equipment being protected. The distance (10 meters) is exclusive of conductors provided with or used to attach SPDs.

Coupling – The means by which power or signals transfer from one circuit element or network to another. Also, the effect of a power or signal source interfering with a signal transmission system.

CPU – An acronym used for the central processing unit of a computer.

Critical load- That portion of electrical/electronic equipment for which power quality is a vital consideration. The term “load” applies to all current-carrying devices on a given circuit or feeder. The term “critical load” refines the language to include only those current-using devices whose operation is considered essential.

Cross talk – The unwanted transfer of energy from one communication circuit to another by means of mutual inductive, capacitive, or conductive coupling.

Crowbar – A circuit that protects sensitive equipment by becoming a “crowbar” (or short circuit) between power conductors when conditions require it and temporarily shunting all current to ground and clamping the voltage
to zero.

CSA – The abbreviation for Canadian Standards Association, a Nationally Recognized Testing Laboratory headquartered in Canada.

Current – The flow of electricity in a circuit as expressed in amperes.Current refers to the quantity or intensity of electrical flow. Voltage, on the other hand, refers to the pressure or force causing the electrical flow.

Current balance – The equal flow of current in each phase of a three-phase power system.

Current carrying – A circuit component carrying current.

Current distortion – Distortion in the ac waveform.See distortion.

Current transformer (CT) – A device that provides a means for measuring current beyond the range of a meter and uses the strength of the field around the conductor to induce a current in its secondary.

Cutout – A device used manually or automatically to interrupt current through any particular apparatus or equipment.

Cycles per second – A term that describes the frequency of alternating current (ac).Frequency is more properly described using the term “hertz“, which is synonymous with cycles per second.

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D

dB - See decibel

dc - See direct current

dc standby current (varistor) – Varistor current measured at rated dc voltage (IEEE 100).

Decibel (dB) – A logarithmic function used to simplify MATV calculations. Decibels may be added or subtracted. 0 dB is the standard reference level for all MATV calculations.

Delta – A standard three-phase circuit connection configured such that the ends of each phase winding connected in series form a closed loop with each phase 120 electrical degrees from the other. It appears as a triangle and looks like the Greek letter delta (r).

Delta connection – A method of connecting a three-phase source or load in series to provide a closed circuit (three-wire, plus ground).

Delta-delta – Three-phase transformer circuit created by a delta source and a delta load with both the primary and secondary winding connected in a delta configuration.

Delta-wye – Three-phase transformer circuit created by a delta source and a wye load with the transformer primary connected in a delta configuration and the transformer secondary connected in a wye configuration.

Demand (kW) – The maximum electrical power, in fifteen minute intervals, that a utility customer requires from the utility.

Derating factor – A factor in percent for reducing the capacity of electrical equipment, like transformers.

Differential-mode voltage – The voltage (noise) that appears across two specified sets of active conductors. See transverse mode noise.

Device failure – An irreversible change in characteristic, resulting in an inability to perform as intended. (SC definition)

Digital multimeter (DMM) – An instrument that measures voltage, current, and resistance and displays measurements on a digital readout.

Diode – A two-terminal device that conducts current better in one direction that the other. It uses include rectification (ac to dc conversion) and detection (retrieving an information signal from a modulated carrier wave).

Diode/capacitor input – A power supply that uses a full-wave bridge rectifier connected to a capacitor to produce a pulse current.

Direct coupling – Two circuits connected to each other through an inductor resistor, or wire.

Direct current (dc) – A unidirectional current whose average value does not equal zero but a constant number.

Direct plug-in – Any SPD incorporating integral blades for direct insertion into a standard wall receptacle. (UL 1449-1996*).

Disk – A memory device which uses a magnetic media for the storage of information. Disk, as a term, has expanded into other areas often used to describe the shape of the storage media, that is: floppy disk, compact disk, laser disk, or hard disk. It sometimes refers to the way in which the storage media mimics a disk media; that is, RAM disk or bubble memory.

Distortion – The wave shape of a signal that is not normal is distorted. Distortion is a term that describes abnormal wave shapes.

Distortion factor – The ratio of the root means square(rms) of the harmonic content of a waveform to the rms of the fundamental quantity, expressed in percent of the fundamental.See total harmonic distortion (THD).

Distribution- The way in which power is routed to various current-using
sites or devices. Outside the building, distribution refers to the process of routing power from the power plant to the users. Inside the building, distribution is the process of using feeders and circuits to provide power to devices.

Disturbance – Any event that adversely affects the normal power flow in a system, such as lightning or a short circuit.

Dropout – Loss of equipment operation due to noise, sag, or interruption. A discrete voltage loss. Or a voltage sag (complete or partial) for a very short period of time (milliseconds).

Dropout voltage - The voltage at which a device fails to operate.

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E

Earth electrode – A ground electrode, water pipe, building steel, or some combination of these, that establishes a building’s earth ground.

Earth ground – A low-impedance path to earth that discharges lightning, static, and radiated energy, and keeps the main service entrance at earth potential.

Eddy currents – Induced currents in transformer winding and core caused by the magnetic field from the normal alternating current and harmonics.

Effective value – For any time-variant voltage or current waveform, the constant value that gives the same average power. For sinusoidal waveforms, the effective value equals 0.707 times the peak value.

Electric field – Describes forces associated with electrical charges.

Electrode – Generally, a conducting medium through which an electric current enters or leaves a different medium, such as an electrolyte, gas, or vacuum.

Electromagnetic – A magnetic field caused by an electric current. For example, the electric current in energized power lines causes electromagnetic fields that can interfere with nearby data cables.

Electromagnetic compatibility – The ability of a device, equipment, or system to function satisfactorily in its electromagnetic environment without introducing intolerable electromagnetic disturbances to anything in that environment.

Electromagnetic interference (EMI) – A term that describes electrically-induced noise or transients.

Electromagnetic susceptibility – The inability of a device, equipment, or system to function without degradation in the presence of an electromagnetic disturbance.

Electrostatic discharge (ESD) – The effects of static discharge can range from simple skin irritation for an individual to degraded or destroyed semiconductor junctions for an electronic device.

EMF – Electromotive force, or voltage.

EMI – See electromagnetic interference

EMP Electromagnetic pulse.

Energy – The capability of doing work over time, expressed in kilowatt-hours for electrical energy.

Equipment grounding conductor – The conductor that connects the non-current-carrying parts of conduits, raceways, and equipment enclosures to the grounded conductor (neutral) and the grounding electrode at the service equipment entrance (main panel) or secondary of a separately derived system (e.g., isolation transformer).See Section 100 in ANSI/NFPA 70-1990.

ESD - See electrostatic discharge

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F

Failure Mode – The observed effects of failure.

Farad – Unit of measurement for capacitance.

Fast tripping (fuse saving) – The common utility protective relaying practice in which the circuit breaker or line recloser operates faster than a fuse can blow. It clears transient faults without a sustained interruption but subject’s industrial loads to a momentary or temporary interruption.

Fault – An unintentional short circuit that causes a failure or interruption in an electrical circuit or a power system.

Fault transient – A short circuit on the power system, usually caused by lightning, tree branches, or animals and cleared by momentarily interrupting the current.

Feeder – An electrical supply line, either overhead or underground, that connects from a generating plant or an interchange point to a load or distribution system.

FERCFederal Energy Regulatory Commission

Field effects – The effects of electric and magnetic fields on objects near current-carrying conductors.

Filter – An electronic device which opposes the passage of a certain band while allowing other frequencies to pass. Filters are designed to produce four different results. Ahigh-pass filter allows all signals above a given frequency to pass. A low-pass filter allows only frequencies below a given frequency to pass. A bandpass filter allows a given band of frequencies to pass while attenuating all others. A trap filter allows all frequencies to pass but acts as a high-impedance device to the tuned frequency of the filter.

Fixed peak current – A desired (specified) test current level which has taken into consideration the additional impedance of the specimen under test, requiring adjustment of the pre-set open-circuit voltage or short-circuit current of the surge generator. (SC definition)

Flashover – Arcing that is caused by the breakdown of insulation between two conductors where a high current flow exists, with a high potential difference between the conductors.

Fluctuation – A change, i.e., surge or sag, in voltage amplitude, often caused by load switching or fault clearing.

Follow currentCurrent supplied by the electrical power system and flowing through the SPD during and following the passage of discharge current.

Forced outage – A power system interruption caused by the improper operation of equipment or human error.

Forward transfer impedance – The amount of impedance between the source and load that affects the transfer of power, including harmonics and inrush current, to the load.

FPN – Fine print note; National Electrical Code® (NEC®) explanatory material.

Frequency – The number of times is a specific period (how frequently, usually in

cycles per second) alternating current(ac) reverses its direction, measured in hertz(Hz). Each reversal from one direction to another and back again constitutes a cycle. In North America, utilities provide power with a frequency of 60 cycles per second, or 60 hertz. In ac circuits, designates number or times per second that the current completes a full cycle in positive and negative directions. See also
alternating current.

Frequency deviation – A variation, i.e., increase or decrease, in the nominal power frequency that can occur from several cycles to several hours.

Frequency modulation (FM) – A method to change a carrier frequency so that it varies above and below a center or resting frequency in step with the signal it transmits.

Frequency response – A measurement of how well a device or circuit transmits various frequencies.

Fuse – An overcurrent protective device with a fusible link that operates and opens the circuit on an overcurrent condition.

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G

Gain – A measure of amplification of a device, usually expressed in dB and at the highest frequency of operation.

Generate – To produce electrical energy.

Generation – The act or process of converting other forms, e.g., mechanical, chemical, solar, or nuclear of energy, into electric energy.

GFI (Ground Fault Interrupter) – A device that interrupts the flow of electric current in an electric circuit when the fault current to ground exceeds some predetermined value.

Ghosting – A signal interference condition producing positive or negative pictures displaced in time from the desired picture, caused by multi-path signal reception. Ghost pictures also result from cable ringing.

Grid – An interconnected system of electric transmission lines and associated equipment that moves or transfers bulk electric energy from the generators to the loads.

Ground – A general term that refers to the point at which other portions of a circuit are referenced when making measurements. Power systems grounding is that point to which the neutral conductor, safety ground, and building ground are connected. This grounding electrode may be a water pipe, driven ground rod, or the steel frame of the building.

Ground block – Connector which passes the RF signal through with minimum loss while providing a means of attaching a ground wire to the drop cable typically near the entry to the home. Grounding is accomplished by either a special ground rod or connection to the water system (See your local code for required grounding methods)

Ground electrode – A conductor or group of conductors in contact with the earth that provides a low-impedance connection to the ground.

Ground fault – Any undesirable current path from a current-carrying conductor to ground.

Ground grid – A system of interconnected bare conductors arranged in a pattern over a specified area, on a buried below the surface of the earth, that provides safety for workers by limiting potential differences within it perimeter to safe levels. It does not act as a signal reference grid.

Ground impedance tester – An instrument that measures the impedance of a circuit from the point of test to the bond between the neutral and ground bond. Some can handle 120 V ac single-phase voltage while others can handle 600 V ac three-phase voltage. It also measures voltage and determines the presence of neutral-to-ground connections, isolated ground shorts, reversed polarity, and an open equipment grounding conductor.

Ground loop - The condition of having two or more ground references in a common system. When two or more grounds have a potential difference between them, current can flow. This flow of current is a new circuit or loop which can interfere with the normal operation of the system.

Ground noise – An undefined, imprecise term that describes unwanted electrical signals appearing between the earth conductor and any other conductor.

Ground potential rise (GPR) – When a large amount of energy is rapidly deposited into the ground by a cloud-to-ground lightning strike or by an electrical fault on a utility power system, the ground potential at this injection point rises to a higher level with respect to the more distant ground. This has the effect of creating a voltage potential gradient in the earth, which can cause dangerous touch and step potentials to personnel exist. By creating an equi-potential ground plane beneath a facility by electrically bonding all separate “grounds” into a “system” or by burying ground mats and meshes, this danger to personnel and equipment can be reduced. It is also important to note that GPR is not only dangerous to personnel, it can also cause damage to equipment.

Ground window – The opening through which all grounding conductors, including metallic raceways, enter a specific area.Provides the building grounding system a connection to an area that would otherwise have a grounding connection.

Grounded – Connected to earth or to some conducting body that substitutes for earth.

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H

Hard-wired – Applied to equipment that connects its power source with wiring (generally customer or contractor-supplied) attached directly to terminal blocks or distribution panels rather than via an input line cord and output receptacle.

Harmonic – A frequency that is a multiple of the fundamental frequency.For example, 120 Hz is the second harmonic of 60 Hz, 180 Hz is the third harmonic, and so forth.

Harmonic content – The waveform that remains after subtracting the fundamental component from a harmonic waveform.

Harmonic distortion - Excessive harmonic content that distorts the normal sinusoidal waveform is harmonic distortion. This can cause overheating of
circuit elements and might appear to a device as data-corrupting noise.

Harmonic resonance – The power quality term that describes the condition that sometimes occurs in electrical systems in which high currents flow through and damage capacitors or clear fuses in connecting circuits. A condition in which the power system resonates at one of the major harmonics produced by nonlinear elements in the system and increases the harmonic distortion.

Henry – Unit of measurement for inductance.

Hertz – A term describing the frequency of alternating current. The term hertz is synonymous with cycles per second. Abbreviated Hz.

High-pass filter – A filter that passes all frequencies above a certain level, and stops all lower frequencies.

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I

IEC  – The International Electrotechnical Commission (IEC) is an international standards-setting body for electrical and electronic technologies.

IEEE - The Institute of
Electrical and Electronic Engineers
(IEEE) is an international society of engineers that develops its own standards.

Impedance – Measured in ohms, impedance is the total opposition to current flow in a circuit where alternating current is flowing. This includes inductive reactance, capacitive reactance, and resistance. Symbol is Z.

Impulse -A surge of unidirectional polarity. Ref: IEEE.

Impulsive transient – A sudden non-power frequency change in the steady-state condition of voltage or current that occurs in unidirectional polarity (primarily either positive or negative.)

Inductance- This term describes the electrical properties of a conductor and its resultant magnetic field when an alternating current is passed through it. This interaction offers an impedance to current flow, thereby causing the current waveform to lag behind the voltage waveform. This results in what is known as a lagging power factor.

Inductor -A discrete circuit element which has the property of inductance. It should be noted that at very high radio frequencies, a straight wire or a path on a printed-circuit board can act as an inductor.

Inductive reactance – The impedance to alternating current produced by inductors.

Insertion loss – Also called “feed through loss”. This is the loss that occurs as signals pass through a passive device. Insertion loss occurs in all devices which do not amplify the signal.

Input line cord – The power cord connected to the input terminals of the uninterruptible power supply (UPS) that plugs into an ac utility outlet to supply power to the UPS.

Inrush current – The initial large current demand needed to start up certain types of electrical equipment, like motors, before their resistance or impedance increases to their normal operating value.

Instantaneous – A qualifying term applied to a circuit breaker or other device indicating that no delay is purposely introduced into its action.

Insulation (electrical) – A dielectric substance or air space permanently offering a high resistance to the passage of current and to disruptive discharge through the substance or space. For example, a  non-electrical-conducting material, like rubber or polyethylene, is used to resist current flow.

Insulation (thermal) – A non-heat-conducting material, like fiberglass, that resists heat flow and provides a barrier to heat loss.

Insulator - A device made of porcelain, glass, rubber, or wood that prevents current from flowing, like a porcelain support that insulates conductors from a pole or tower.

Isolation – The degree to which a device can separate the electrical environment of its input from its output, while allowing the desired transmission to pass across the separation.

Interconnection system – A connection between two electrical systems that allows the transfer of electric energy in either direction.

Internal impedance – The inherent impedance inside a device or circuit.

Interruptible power – Power that the supplier and the customer have agreed can be stopped by the supplier.

Interruption, sustained (power quality) – The complete loss of voltage (<0.1 pu) on one of more phase conductors for a long time period greater than 1 minute.

Inverter – An inverter converts dc power into ac power.

Isolated ground – An insulated equipment grounding conductor that runs in the same conduit or raceway as the supply conductors and is insulated from the metallic raceway and all ground points throughout its length. It originates at an isolated ground-type receptacle or equipment input terminal block and terminates at the point where neutral and ground bond at the power source. See NFPA 70-1990, Section 250-74, Exception 4, and Section 250-75, Exception.

Isolation – Separation between electrical input and output, such as an isolation transformer or optical coupler or separation of one section of a system from the undesired influences of other sections.

Isolation transformer - A multiple-winding transformer with physically separate primary and secondary windings that allows the magnetic field in the winding of the primary to create (induce) electrical power in the secondary winding but minimizes electrostatic transfer to the secondary windings. This way the electrical power available at the input transfers to the output, but some of the unwanted electrical effects in the input power do not reach the transformer’s output.

ITIC (Information Technology Industry Council) - replaced the former Computer Business Equipment Manufacturers Association.

ITIC Curve - Replaces the former CBMA curve and provides a set of curves developed by the Information Technology Industry Council (ITIC) that represents the withstand capabilities of computers in terms of the magnitude and duration of the voltage disturbance.

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J

Joule – The surge energy (watt seconds) that the device is capable of absorbing.

Jumper – A short length of conductor that connects two points in a circuit.

Junction box (J box) – A box with a blank cover that provides space to connect and branch enclosed conductors.

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K

k-rated transformer – A transformer specially designed to handle harmonics.

Kilovolt-Ampere (kVA)- An electrical unit related to the power rating of a piece of equipment. It is calculated by multiplying the rated voltage of equipment by the current required (or produced).For resistive loads 1 kilovolt-ampere equals 1 kilowatt.

Kilohertz (kHz) – A term meaning 1000 cycles per second.

Kilowatt (kW) – The product of the root-mean-square (RMS) current, the root-mean-square (RMS) voltage, and the power factor divided by 1000.

Kilowatt-hour (kWh) – The basic unit of electric energy that equals 1000 watts of power used for 1 hour. The amount of power the customer uses is measured in kilowatt-hours (kWh).A measurement of power and time used by utilities for billing purposes.For example, a 75-watt light bulb that burns for 10 hours consumes 0.75 kWh (75 watts x 10 hours) or 750 watt-hours.

Kirchhoff’s laws of electric networks – The sum of the electrical currents flowing to a point in a network equals the sum of the currents flowing away from that point.

KVA (1000 VA) – The product of the root-mean-square (RMS) current and the root-mean-square (RMS) voltage divided by 1000; provides the actual measured apparent power and is used for circuit sizing.

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L

Lag – The time delay between two events (usually electrical quantities), such as delay of current behind voltage.

Lagging load – An inductive load that resists changes in current in which current lags voltage. The time lag between current and voltage is measured in electrical degrees and is known as the phase angle. The cosine of this angle equals the power factor (linear loads only).

LAN (Local Area Network) – A data communications system confined to a certain area. The area served may consist of a single building, or a cluster of buildings.

LC circuit – An electric network that contains both inductive and capacitive elements.

Leading load – A capacitive load that resists changes in voltage with current leading the voltage.

Leakage current – Any current, including capacitively coupled currents, that may be conveyed from accessible parts of a product to ground or to other accessible parts of the product. (UL 1449)

Leased line – A dedicated circuit, typically supplied by the telephone company, that permanently connects two or more user locations. These lines are used to transmit data.  See T1.

LED (light emitting diode) – A semiconductor that emits light when current passes through it.

Lifetime rated pulse currents (varistor) – Derated values of Itm for impulse duration’s exceeding that of an 8/20 us wave shape, and for multiple pulses which may be applied over device’s rated lifetime. (IEEE 100)

Lightning arrester – See surge arrester.

Line - A designation of one or more power-carrying conductors for power distribution. The black (or red or blue) wire is the line conductor, the white wire is the neutral, and the green wire is ground. The voltage difference between the line conductor and the neutral is the supply voltage, i.e., 120 volts.

Line conditioner - A line conditioner contains multiple protection devices in one package to provide, for example, electrical noise isolation and voltage regulation.

Line filter – A filter in series with a transmission line that removes unwanted electrical signals.

Line imbalance – Unequal loads on the phase lines of a multiphase feeder.

Line loss – The heat loss in a line caused by the flow of the current through the resistance in the line, usually called I2R loss.

Line to Line
(L-L) – A term used to describe a given condition between conductors of a multiphase feeder.

For normal mode protection, the SPD should provide protection between each current carrying conductor pair (L–L and L–N).For common mode protection, the SPD should provide protection between the line-to-ground (L–G) and/or neutral-to-ground (N–G) modes.

Line to Neutral (L-N) – A term used to describe a given condition between a phase conductor and a neutral conductor.

For normal mode protection, the SPD should provide protection between each current carrying conductor pair (L–L and L–N).For common mode protection, the SPD should provide protection between the line-to-ground (L–G) and/or neutral-to-ground (N–G) modes.

Linear load – An electrical load device, which, in steady-state operation, provides an essentially constant load impedance to the power source throughout the applied voltage cycle and in which the current relationship to voltage remains constant for a relatively constant load impedance.

Load – Any electrical device connected to a power source may be called by the general term of “load”.

Load balancing – Switching the various loads on a multiphase feeder to equalize the current in each line.

Load fault – A malfunction, like a tree touching a power line, that causes the lead to demand abnormally high amounts of current from the source.

Load unbalance – Unequal loads on the phase lines of a multiphase system.

Loss – The power dissipated in a power system circuit expressed in watts. In communications, the ratio of the signal power delivered by a device under ideal conditions to the signal actually delivered expressed in decibels (dB).

Low-pass filter – A filter that passes all frequencies below a certain designated cutoff point and blocks all frequencies above that point.

 

*(Note: UL 1449 Third Edition went into effect September 2009. Updates pending.)

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M

Magnetic field- The lines of force that exist around an energized electrical conductor, magnet, or inductor.

Main service disconnect overcurrent device – The first overcurrent device between the secondary terminals of the distribution or power class transformer and the load terminals of the service entrance equipment. Also identified as the service entrance main.

Main service entrance — The enclosure that contains connection panels along with fuses or breakers, and located at the point where the utility power lines enter a building.

Mains – The ac power source available at the point of use in a facility.It consists of the set of electrical conductors (referred to by terms including “service entrance”, “feeder”, or “branch circuit”) for delivering power to connected loads at the utilization voltagelevel. Ref. IEEE 100.

Maintenance bypass – A circuit that allows maintenance personnel to repair or service equipment without affecting supply of electricity to other equipment.

Matching transformer- A device, often called a balun, which converts between a 75 ohm impedance and a 300 ohm impedance.

Mean Time Between Failure (MTBF) – A statistical estimate of the time a component, subassembly, or operating unit will operate before failure will occur.

Measured limiting voltage – The maximum voltage that is measured across the terminals of the SPD during the application of impulses of a specified waveshape and amplitude.

Megahertz (MHz) –A term for one million hertz(cycles per second).

Metal oxide varistor (MOV) – A solid state device which becomes conductive when the voltage across it exceeds a certain level.When the voltage exceeds the MOV’s threshold, current flows through the MOV.

Meter board – The board on which the main switch and associated equipment mount.

Meter constant – The ratio of the output of an instrument transformer (current transformer, power transformer) to the input of the meter to determine the difference between meter readings to determine the kilowatt-hours used.

Meter inspection – An examination of the meter to determine its accuracy.
Meter loop (meter socket) – The necessary equipment and wiring that the customer’s electrician install prior to the meter installation.

Meter test – An instrumental test of meter accuracy under all load conditions.

Micro (µ) – A metric prefix that means one-millionth of a unit, or 10-6.

Microwaves – Ratio frequencies of 1000 megahertz or greater that have very short wavelengths and exhibits some of the properties of light and allow communication signals sent point-to-point in a concentrated beam.

Minimum ground clearance – The least distance between a conductor and ground level under selected design-loading conditions.

Mitigate (power quality) – The reduction of power quality disturbances by the use of power conditioning equipment.

Modem – A hardware device that converts digital computer data into analog tones that can be transmitted over dial-up telephone circuits.

Modes of protection – Electrical paths where the SPD offers defense against transient overvoltages. Examples include, Line to Neutral (L-N), line to Ground (L-G), Line to Line (L-L) and Neutral to Ground (N-G).

Module – A sub-unit of an electronic system that can be plugged in or otherwise easily replaced.

Momentary over-voltage (voltage swell) - A temporary increase in the rms value of the voltage or current of more than 10 percent of the nominal voltage, at the power frequency, for any duration from 0.5 cycle to 1 minute.

Moore’s Law – The principle by which, in the computer industry, each new chip contains roughly twice as much capacity as its predecessor released 10 to 24 months previously. Named after an Intel founder, Gordon Moore, who made this observation in a 1965 speech.

Motor alternator – A device that consists of an ac
generator mechanically linked to an electric motor, which is driven by utility power or by batteries. An alternator is an ac generator.

Motor generator - A motor generator consists of an ac motor coupled to a generator. The utility power energizes the motor to drive the generator, which powers the critical load. Motor generators provide protection against noise and spikes, and, if equipped with a heavy flywheel, they may also protect against sags and swells.

 

MTBF - See mean time between failure

Multi-Port SPD – Pending a resolution of different definitions among standard-writing bodies, the terms ‘multi-port’ has not been used in this protocol.

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N

Nameplate rating – The full-load continuous rating of a specific electrical apparatus, like a transformer or generator, under specified conditions set by the manufacturer.

National Electrical Code® – A set of rules and regulations, plus recommended electrical practices, published by the National Fire Protection Association. Abbreviated NEC.®

NEC®- See National Electrical Code®

Negative sequenced – Occurs when a three-phase electrical quantity, such as voltage, current, or power, crosses the zero line in the order of A-C-B rather than A-B-C.

NEMA  – The National Electrical Manufacturers Association (NEMA) is a standards-setting body for electrical equipment.

Network – A system of transmission and distribution lines cross connected and operated to permit multiple power supply to any principal point on it. It provides a high level of reliability by restoring power quickly to customers during an outage by switching them to another circuit.

Neutral – The grounded junction point of the legs of a wye circuit or the grounded center point of one coil of a delta transformer secondary.

Neutral conductor – One of the conductors of a three-phase wye system. Sometimes called the return conductor, it carries the entire current of a single-phase circuit and the resultant current in a three-phase system that is unbalanced. The neutral is bonded to ground on the output of a three-phase delta-wye transformer.

Node – A point of connection to a network. Also referred to as a device, workstation, printer, computer, or any other point of connection to a network.

Noise – An undesirable signal. A distortion of the normal sine wave. Can be caused by radar and radio transmitters, fluorescent lights, power control circuits, acing utility and industrial equipment.

Noise-conducted – Any signal of greater than 1000 times the fundamental power frequency (60Hz) with a magnitude of less than twice the RMS voltage of the distribution system. It is superimposed on the power waveform and is in the range from 100kHz to 100MHz.

Nominal rate of rise (of an impulse wave front) – The slope of the line that determines the virtual zero. It is usually expressed in volts or amperes per microsecond.Ref. IEEE 100.

Nominal system voltage – A nominal value assigned to designate a system of a given voltage class. Note: See ANSI C84.1. Ref. IEEE 100.

Nominal varistor voltage – The voltage across the varistor measured at a specified pulsed dc current, IN(dc), of specific duration. IN(dc) is specified by the varistor manufacturer.Ref. IEEE 100.

Nominal voltage – The normal or specified voltagelevel.For three-phase wye systems, nominal voltages are 480/277 V (600/346 V in Canada) and 208/120 V, where the first numbers expresses phase-to-phase (or line-to-line) voltages and the second numbers equals the phase-to-neutral voltage. The nominal voltage for most single-phase systems is 240/120 V.

Nonlinear load – A load in which the current varies with the voltage in a nonlinear fashion.For example, in a switched-mode power supply or almost any other electronic power supply.The current does not vary in direct proportion to the voltage because it uses power in pulses or other waveforms that to not track the sine wave.

Nonlinear load current – Current drawn by a load that does not have a direct relationship to the voltage waveforms.

Normal mode (NM) – Refers to electrical interference measured between line and neutral (current-carrying conductors). The operation of lights, switches and motors generates normal-mode interference.

Normal-mode noise - A noise signal which appears between a set of phase conductors, irrespective of their associated ground conductor.

Notching – A negative or positive change in the wave-shape that repeats cycle to cycle, caused by light peak currents of variable-speed drives or other phase loads.

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O

OCV - See open-circuit voltage

Off-line – Describes the operating of a standard utility power system that supplies power directly to the load and then transfers to battery power supplied through an inverter when the voltage drops below a specified level.The time required between the loss of utility power and inverter start-up can disrupt sensitive loads.

Ohm (Ώ)- The unit of measurement for resistance (symbol R), impedance(symbol Z), and reactance (symbol X).

Ohm’s law – The relationship between voltage (pressure), current (electron flow), andresistance. The current in an electrical circuit is directly proportional to the voltage and inversely proportional to the resistance: E = IR, I = E/R, and R = E/I, where E = voltage, I = current, and R = resistance.

On-line – Describes the operation of an uninterruptible power system which supplies conditioned power through an inverter or converter to the load and supplies the backup power to the load without delay when a utility power outage occurs.

One-port SPD – A surge protective device (SPD) having provisions (terminals, leads, plug) for connection to the ac power circuit but no provisions (terminal, leads, receptacles) for supplying current to the ac power loads(UL 1449-1998)

Open circuit – Describes the condition of a disconnect in a circuit caused intentionally or by a fault.

Open-circuit voltage (OCV) – The voltage available from the test set up (surge generator, coupling circuit, back filter, connecting leads) at the terminals where the surge protective device (SPD) under test will be connected. (SC definition)

Orderly Shutdown - The turning off of power to computer devices in such a way that data is not lost or corrupted.

Oscillation – The change with time of a quantity’s value from the maximum and minimum values of one cycle.

Oscillatory transient – A power quality term that describes a voltage or current transient that rises suddenly and sharply to some level and then degrades over time to a waveform that decreases in frequency and amplitude.

Oscilloscope – An electronic instrument that produces a visible graphical display on a cathode-ray tube of the instantaneous value of one or more rapidly varying electrical quantities as a function of time or other electrical or mechanical quantity.

Out of phase – A condition that occurs when two waves have the same frequency, but their maximum values occur at different times.

Outage – See blackout.

Output – The current, voltage, power, or driving force that a circuit or a device delivers.

Output impedance – A measure of a source’s ability to supply current to a load.

Overload – A condition when the flow of electricity exceeds the rated capacity of a device or system or when the load wants more from the power source, utility, or UPS than the power source can supply.

Overload capacity – The maximum load that a machine, apparatus, or device can carry beyond its normal nameplate rating without damaging itself.

Overvoltage – An increase in the normal voltagelevel lasting for seconds or minutes greater than the rating of a device or component. The term can also apply to transients and surges. When applied to a long-duration variation it refers to a voltage with a value at least 10 percent above the nominal voltage for a period of time greater than 1 minute.

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P

Pad-mount transformer – A transformer inside a large metal cabinet on a pad outside a house or building that converts the utility voltage supplied via an underground line to a level that a customer can use (120/240 V for a home), similar to a pole-mounted transformer.The cabinet has a lock and a “DANGER” sign on it.

Panelboard – A single panel or group of panel units assembled into a single panel, containing buses and, over-current protection devices (with or without switches) to control power circuits.

Parallel operation – The connection of two or more components side by side to the same pair of terminals to increase the capacity of the power system or provide power redundancy. For example, paralleling for capacity two transformers means that two
50-kVA units in parallel have the sum of their individual ratings, i.e., the power of a single 100-kVA transformer. Paralleling two UPS units for redundancy means that if one fails, the other unit will provide backup power.

Passive filter – A combination of inductors, capacitors, and resistors that eliminates one or more harmonics.The most common type simply uses an inductor in series with a shunt capacitor, which diverts the major distorting harmonic component from the circuit.

Patch Panel – A device which consolidates cables in a central location, allowing for easy changes.

PDU - See power distribution unit

Peak – The maximum instantaneous measurement of an electrical event.

Permanently connected SPD – Any SPD provided with terminals or leads for field connection to wiring systems in accordance with the National Electrical Code® – ANSI/NFPA-70). This includes receptacle/type SPDs intended for installation in outlet boxes.(UL 1449-1998*)

Periodic waveform – A waveform that repeats itself after a period of time.

Phase – The stage or progress of a cycle movement, such as a current or voltage
wave.Also a conductor that carries one of three separate phases (designated, A, B, and C) of power in al alternating current system.Almost all residential customers use either two-phase or three-phase service.

Phase angle – In a power system, the displacement, in time, of the phase of one quantity from the phase of another, at power system frequency.

Phase balancing – Connecting loads in a three-phase power system so that all three phases carry the same current.

Phase compensation – Switching capacitors into or out of a power distribution system to reduce the phase difference between the current and voltage to keep to power factor close to unity.

Phase conductor – The wire cable in each phase of a transmission or distribution line.

Polarity – An electrical condition that determines the direction in which current tends to flow.

Polyphase – An alternating current (ac) supply with two or more hot conductors.Voltages between the conductors and the voltage waveforms for each conductor are usually displaced 120 degrees.The voltage from each hot conductor to neutral is equal.

Power – A general term which means the capacity for doing work. In the electrical environment, this is usually measured in watts.

Power conditioner – See line conditioner.

Power distribution unit (PDU) – A portable electrical distribution device that provides an easily expandable and flexible electrical environment for a computer and its associated peripherals.

Power disturbance – A disturbance, like a surge or sag, that originates from the utility’s power system.

Power quality – A general term describing the powering and grounding of electronic equipment in a manner suitable to the operation of the equipment and compatible with the premise wiring system and other connected equipment.

Power quality problem – The difference between the quality of electricity at an electrical outlet and the quality of the electricity required to reliably operate an appliance, resulting in a malfunction or damage.

Power warning fault (PWF) – An option in a UPS that supplies a warning signal to some computer systems that the UPS may shut down. Some computers can take advantage of this signal to automatically back up and shut down before the UPS shuts down.

Power-line monitor – An instrument that monitors the condition of the power supplied to a given load.

Propagation – The travel of an electrical waveform along a medium, as in a surge passing along a power cord to a system.

Protective scheme – A group of interrelated devices that prevent damage to equipment caused by very high voltages and currents.

Pulse life – The number of surges of specified voltage, current amplitudes, and waveshapes that may be applied to a device without causing degradation beyond specified limits. The pulse life applies to a device connected to an ac line of specified characteristics and for pulses sufficiently spaced in time to preclude the effects of cumulative heating. Ref. IEEE 100.

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R

Radial array – A group of earthing electrodes or conductors of equal length and ampacity, connected at a central point and extending outward at equal angles, spoke fashion, to provide a low-earth-impedance reference.

Radiation — RF energy which is emitted or leaks from a distribution system and travels through space. These signals often cause interference with other communication services.

Radio-Frequency Interference (RFI) – Electromagnetic signals of a frequency associated with electromagnetic radiation which are coupled to a conductor either directly or as with an antenna.

Rated Temporary Overvoltage (TOV) Withstand Level – Combination of magnitude and duration of a temporary overvoltage that the SPD can withstand without changes in characteristics or functionality, as declared by the manufacturer.

Reactance – A physical property of a circuit component that tends to hinder the flow of alternating current.

Reactive power – The out-of-phase component of the total volt-amperes in an electric circuit that represents the power required to provide a magnetic field to drive reactive loads, like motors, in a circuit. Expressed in VARs (volt amperes reactive).

Real power – The in-phase component of volt-amperes in an electric circuit that does useful work, expressed in watts or kilowatts.

Receiver – the part of a communications system which converts electrical waves into visible or audible form.

Recovery voltage – The voltage that occurs across the terminals of a circuit interrupting device when it interrupts the flow of electricity.

Redundancy – The addition of extra components in an electrical power system that provide backup in the event of loss of any of those components.

Reflection – The return wave created when a traveling wave encounters load, a source, or a junction that has a change in line impedance.

Regulation – A term used to describe the action of holding a constant electrical value in the face of fluctuations.

Relay – An electromagnetic device that interprets input conditions (which reflect the operation of another piece of equipment) in a prescribed manner, and after specified conditions occur, responds to cause contact operation or similar abrupt change in a circuit controlling the equipment.

Resistance – A term describing the opposition of elements of a circuit to alternating or direct current. Symbol is R.

Resistor – A discrete electronic component designed to produce a dc voltage drop when dc current passes through it.

Resonance – The condition that occurs when the capacitive reactance equals the inductive reactance of a circuit.

Response time – The time required, after the initiation of a specified disturbance to a device or system, for an output to reach a specified value.

Response Time (Varistor) – The time between the point at which the wave exceeds the clamping voltage level and the peak of the voltage overshoot. For the purpose of this definition, clamping voltage is defined with an 8/20 m current waveform of the same peak current amplitude as the waveform used for this response time. Ref. IEEE 100.

RFI(Radio-Frequency Interference) - Electromagnetic signals of a frequency associated with electromagnetic radiation which are coupled to a conductor either directly or with an antenna.

Ride-through – The ability of a power conditioner, specifically a UPS, to continue to supply power to critical loads when the utility has discontinued power.

Ripple – An alternating current (ac) component on a direct current (dc) voltage resulting from incomplete filtering, usually associated with the ac component that appears on the output of the dc power supply.

RMS – See root means square

Rolling blackout – An unplanned outage by the utility that could be caused by nature or demand exceeding generation where the utility’s system systematically collapses.

Root Means Square (RMS) – Used for ac voltage and current values that equal the square root of the average of the squares of all the instantaneous amplitudes occurring during one cycle. Referred to as the effective value of ac because it equals the value of ac voltage or current that causes the same amount of heat produced in a circuit containing only resistance from a dc voltage or current of the same value. In a pure sine wave the RMS value equals 0.707 times the peak value and the peak value equals 1.414 times the RMS value. The normal home wall outlet, which supplies 120 V RMS, has a peak voltage of 169.7 V.

Rotating field – The electrical field that develops in a multiphase generator caused by the varying currents flowing through parts of a stator winding.

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S

Safety Ground - A conductive path that bonds all cabinets and conductor shields to the power-source ground.

Sag (also called dip or voltage sag) - An RMS reduction in the ac voltage, at the power frequency, for durations from a ½ cycle to a few seconds. Ref. IEEE 1100.

SCC - See Short Circuit Current

Scheduled outage – An outage that results when the utility (or facility) deliberately removes from service at a selected time a component of the power system, usually to allow construction, maintenance, or test.

SCR – See Silicon Controlled Rectifier

Secondary circuit – The distribution circuit on the low-voltage side of a transformer (usually 120/240 V).

Semiconductor – An electronic conductor (e.g., silicon, selenium, or germanium) with a resistivity between metals and insulators that allows current to flow through it normally via holes or electrons.

Series capacitor – In a power system, a capacitor that compensates for voltage drop along a transmission line and reduces the impedance of the transmission line to allow more power to flow in it.

Service drop – The lines running to the customer’s house that usually includes two 120-V lines and a neutral line, from which the customer can obtain either 120- or 240-V power. When these lines are insulated and twisted together, they become triplex cable.

Service entrance equipment – The main control and means of disconnection for the supply of electricity to a building that usually contains circuit breakers, switches, and fuses.

Shielding – Protective coating that helps eliminate electromagnetic and radio frequency interference.

Short Circuit – An accidentally established connection between two points in an electric circuit, as when a tree limb or an animal bridges the gap between two conductors.This will cause an overload of current on the line, causing damaged lines, blown fuses, and the operation of protective devices such as reclosers and circuit breakers.

Short Circuit Current (SCC) – The current which the test set up (surge generator, coupling circuit, back filter, connecting leads) can deliver at the terminals where the SPD under test will be connected, with the SPD replaced by bonding the two lead terminals. (Also sometimes abbreviated as “SCI”) (SC definition)

Short Circuit Current Rating (SCCR) of a surge-protective device – The level at which a surge-protective device (SPD) is suitable for use on an ac power circuit that is capable of delivering not more than the declared root-mean-square symmetrical current at a declared voltage during a short-circuit condition.

Short-duration variation – A variation of the RMS value of the voltage from nominal voltage for a time greater then ½ cycle of the power frequency but less than or equal to 1 minute. Usually further described by a modifier indicating the magnitude of the voltage variation. (e.g., sag, swell, or interruption) and possibly a modifier indicating the duration of the variation (e.g., instantaneous, momentary, or temporary).

Shunt – A device having appreciable resistance or impedance connected in parallel across other devices or apparatus and diverting some (but not all) of the current from it. Ref. IEEE 100.

Shunt filter – A filter connected in parallel across a device or circuit to filter out undesirable signals.

Signal – A visual, audible, electrical, or other representation that conveys confirmations, or an electronic wave that embodies information.

Signal-To-Noise Ratio(SIN) – The ratio of desired signal level to the undesired noise level, expressed in dB.

Silicon avalanche diode – A semiconductor device that normally acts as an open circuit but changes to a short circuit when the trigger voltage exceeds a certain amount.

Silicon Controlled Rectifier (SCR) – A device that acts as an electronic dc switch when triggered to conduct by a pulse or a gate signal, and cuts off the flow of electricity by reducing the main current bellow a predetermined level (usually zero).

SIN - See Signal-To-Noise Ratio

Sine Wave - A fundamental waveform produced by periodic oscillation that expresses the sine or cosine of a linear function of time or space, or both.  More on sine wave tracking technology.

Single Phase – A line that carries electrical loads capable of serving the needs of residential customers, small commercial customers, and streetlights.It carries a relatively light load compared to heavy-duty three-phase constructs.With a three-phase source: one or two phase conductors. With a single-phase source: a single output that may be center-tapped for dual voltage levels.

Single-phase condition – An unusual condition where one phase of a three-phase system is lost, causing unusual effects on lighting and other loads.

Single-Point Ground – The practice of tying the power neutral ground and safety ground together at the same point, thus avoiding a differential ground potential between points in a system. More information>>

Sinusoidal – A waveform that can be represented by a sine function.

Skin effect – The tendency of a high frequency current flowing in a conductor to flow near the surface of the conductor.
The current may be a radio frequency or a transient surge current.

SPD disconnector – A device for disconnecting a surge protective device (SPD) from the system in the event of SPD failure.It is to prevent a persistent fault on the system and to give visible indication of the SPD failure.Note: At least three functions are needed for SPD disconnectors: protection against thermal problems (such as thermal runaway on varistors), protection against internal short circuits, and protections against indirect contact.These functions may be achieved by one or several devices.They may be used in the SPD circuit or in the mains.(IEC TC37)

Soft-start circuit – Circuitry that limits the initial power demand when an UPS is operated in emergency mode and commercial power comes back on. It also controls the rate at which the UPS output increases to normal.

Solid-state – Describes an electronic device whose electrical functions are performed by semiconductors (as opposed to components that conduct in a vacuum or gas, such as tubes) and otherwise completely static components, such as resistors and capacitors.

Spark gap – Any short air space between two conductors electrically insulated from each other; or a device that depends on a spark gap for its operation.

SPD - See Surge-Protective Device

Spike (or impulse, switching surge, lightning surge) – These terms refer to a voltage increase of very short duration (microsecond to millisecond). Spikes may be caused by lightning, switching of heavy loads, and/or short circuits or power system faults.

Standby current – The current flowing in any specific conductor when the SPD is connected as intended to the energized power system at the rated frequency with no connected load.Ref. IEEE 100.

Standby power supply(SPS) - See uninterruptible power supply.

Static switch – A solid-state device that opens and closes circuits without the use of moving mechanical parts.

Suppressed voltage rating (UL) – A discreet rating per UL 1449 standard, signifying the rounded up average clamping voltage of an SPD when subjected to the Measured Limited Voltage test. Said test consists of one 6kV 500A, 8/20µs waveform, followed by ten positive, ten negative, 6kV 3kA 8/20µs waveform duty cycle impulses, and one final 6kV 500A, 8/20µs waveform (60 second intervals). Any device with a deviation of 10% or greater from the first to last impulse is considered failed, per the standard.

Surge – A surge is a transient voltage or current with a duration of a few microseconds.

Surge arrester – A protective device for limiting surge voltages by discharging or bypassing surge current, and it also prevents continued flow of follow current while remaining capable of repeating these functions. Ref. IEEE 100.

Surge-protective device (SPD) – Is the generic term used to cover both Surge Arresters (including secondary surge arresters) and Transient Voltage Surge Suppressors (TVSS) devices. An SPD is a non-linear protective device for limiting surge voltages on equipment by discharging, bypassing, or diverting surge current; it prevents continued flow of follow current and is capable of repeating these functions as specified.

Surge response voltage – The voltage profile appearing at the output terminals of a protective device and applied to downstream loads, during and after a specified impinging surge, until normal stable conditions are reached.Ref. IEEE 100. (See also, clamping voltage)

Surge suppressor – See SPD.

Sustained – When applied to quantity the duration of a voltageinterruption, refers to the time frame associated with a long duration variation (i.e., greater than 1 minute).

Swell - See momentary over-voltage.

Switched-mode power supply – A power supply that uses electronic components to convert ac power into high-frequency dc power.

Switchgear – A group of switches, relays, circuit breakers, etc., that controls the distribution of power to other distribution equipment and large loads. Also, substation equipment designed and operated to switch electrical circuits and interrupt power flow.

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T

T1 – AT&T term for a digital carrier facility used to transmit a formatted high speed digital signal. See Leased Line.

Temporary Overvoltage(TOV) – An oscillatory over-voltage that is undamped or slightly damped.

Three phase – An electrical system with three different voltage lines or legs, which carry sine-wave waveforms that are 120° out-of-phase from one another.

Thermal runaway – An operational condition when the sustained power loss of an SPD exceeds the dissipation capability of the housing and connections, leading to a cumulative increase in the temperature of the internal elements culminating in failure. (IEC TC37)

Thyristor – A semiconductor bistable switch (with on and off states) that operates uni-directionally or bi-directionally.A three-terminal device (a controlled rectifier) or a two-terminal device (diode may trigger it).

Total demand distortion (TDD) – The ration of the root mean square (rms) of the harmonic current to the root mean square value of the rated of the rated or maximum demand fundamental current, expressed as a percent.

Total harmonic distortion (THD) – The ratio of the root mean square (rms) of the harmonic content to the root mean square value of the fundamental quantity, expressed as a percent of fundamental, that describes a wave-shape change caused by the presence of multiples of the fundamental frequency of the ac power.The square root of the sum of the squares of the rms harmonic voltages or currents divided by the rms fundamental voltage or current.

Transfer switch – A switch that transfers load from one source to another.

Transformer – A device used for changing the voltage of an ac circuit and/or isolating a circuit from its power source.

Transient – An electrical event of a nonrepetitive nature. the term is used interchangeably with the term “impulse“; however, the term relates more to the intermittent occurrence of “surges” and “sags“.A short duration, fast-rise-time voltage caused by lightning, large motors starting, utility switching operations, and other appliances switching.

Transient response – The ability of a power conditioner to respond to a change in voltage or power.

Transient step load response – The ability of a power conditioner to maintain a constant output voltage when sudden load (current) changes occur.

Transient voltage surge suppressor (TVSS) - See surge protective device.

Transverse mode noise (normal mode) – An undesirable voltage that appears from line to line of a power line.

Trip-out – A disconnection of an electric circuit that occurs when the circuit breaker has opened, putting the line out of service; usually refers to an automatic rather than a manual action.

Triplen harmonics – Odd multiples of the third harmonic, which deserve special attention because of their natural tendency to add to each other.

Two-port SPD – An SPD having provisions (terminals, leads, plug) for connection to the ac power circuit and provisions (terminals, leads, receptacles) for supplying current to one or more ac power loads. SPDs provided with a minimum of two adjacent terminals for each circuit conductor may be considered and tested as a two-port SPD.

Traverse-mode noise – Often used as a synonym for normal-mode noise, it more clearly relates to noise that is the result of the conversion of common-mode noise to normal-mode noise after it passes through a transformer.

TVSS – See surge protective device

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U

UHF (Ultra High Frequency) - Off-air television channels 14-83.

UL – The abbreviation for Underwriter’s Laboratories,Inc., a Nationally Recognized Testing Laboratory headquartered in the United States.

UL 1449 (Underwriters Laboratories Standard Number 1449) – A nationally recognized set of guidelines used by UL to evaluate surge protective devices.

Undervoltage – Like a sag, but for a longer period of time: over 2.5 seconds.

Uninterruptible power supply (UPS) (see also motor-generator) – Non-mechanical (static) uninterruptible power supplies can provide protection against all power disturbances. An on-line or “true” UPS converts the utility ac power to dc and uses the dc to charge a battery and to power an inverter that delivers power to the critical load.
An off-line UPS, more properly called a standby power supply (SPS), supplies the utility power directly to the critical load and transfers the load to a battery-powered inverter to supply power during outages.

UPS – See uninterruptible power supply

Utility power –Alternating current (ac) supplied to the user by the (usually commercial) electrical utility. May be subject to spikes, sags, swells, electrical noise, and outages.

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V

Varistor – A semiconductor device whose resistance varies with the applied voltage.

VHF (Very High Frequency) – Off-air television channels 2-13.

Voice-grade line – A telephone line that is capable of carrying analog voice-frequency signals.

Volt – Electrical unit of measure (current x resistance).

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 voltages are expressed as phase to phase or phase to neutral.The unit of measurement is volts and the electrical symbol is V.

Voltage distortion – Any change from the nominal voltagesine waveform.

Voltage interruption – Disappearance of the supply voltage on one or more phases. Usually qualified by an additional term indicating the duration of the interruption (e.g., momentary, temporary, or sustained).

Voltage-limiting type SPD -A surge protective device (SPD) that has a high impedance when no surge is present, but will reduce it continuously with increased surge current and voltage. Common examples of components used as nonlinear devices are: varistor and suppressor diodes. These SPDs are sometimes called ‘clamping type’. Note – A voltage-limiting device has a continuous V versus I characteristic. Ref. IEC TC37.

Voltage regulator – Voltage regulators control the output voltage, eliminating voltage sags and swells in the input voltage that last from 15 milliseconds to one-half second. They are typically relatively inexpensive feedback-controlled transformers.

Voltage-switching type SPD – An SPD that has a high impedance when no surge is present, but can have a sudden change in impedance to a low value in response to a voltage surge. Common examples of components used as nonlinear devices are: spark-gaps, gas tubes, thyristors and triacs.These SPDs are sometimes called “crowbar type”. Note – A voltage-switching device has a discontinuous V versus I characteristic.Ref. IEC TC37.

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W

Watt (power) -The unit of power that equals 1 joule per second. The mathematical relationship, between watts, volts and amperes is wattage = ampere x voltage.

Watt-hour – The amount of power used by one watt in one hour.

Watt-hour meter – An electric meter that measures and registers the energy (kilowatt-hours) delivered to a circuit.

Waveform – A graph of a wave that shows its shape and changes in amplitude with time.

Waveform distortion – A steady-state deviation from an ideal sine wave of power frequency principally characterized by the spectral content of the deviation.

Wye – A wye connection refers to a polyphase electrical supply where the source transformer has the conductors connected to the terminals in a physical arrangement resembling a Y. Each point of the Y represents the connection of a hot conductor. The angular displacement between each point of the Y equals 120. The center point provides the common return point for the neutral conductor.

Wye-delta – Transformer connection with a wye primary and delta secondary.

Wye-wye – Transformer connection with a wye primary and wye secondary.

Z

Zero sequenced – All three phases of a power system intersect the zero axis at the same time.

Zero signal reference – A connection point, bus, or conductor used as one side of a signal circuit that may or may not be designated as ground; sometimes referred to as circuit common.

Zigzag transformer – A special type of transformer used to change the phase angle of the transformer primary.

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