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Electrical Glossary

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Alternating Current.


The accuracy of a digital tester is defined as the difference between the reading and the true value for a quantity measured in reference conditions. Accuracy is specified in the format: (±xx% rdg ±xx dgt) The first portion identifies a percentage error relative to the reading, which means it is proportional to the input. The second portion is an error, in digits, that is constant regardless of the input. "Rdg"is for reading and "dgt"is for digits. Dgt indicates the counts on the last significant digit of the digital display and is typically used to represent an error factor of a digital tester.

Active Power

A term used for power when it is necessary to distinguish among Apparent Power, Complex Power and its components, and Active and Reactive Power. See Ampère-Hour

Ampère (A)

The unit expressing the rate of flow of an electric current. One Ampère is the current produced by a difference in potential of one volt across a resistance of one ohm; An electic current flowing at therate of one coulomb per second.

Ampère-Hour (Ah)

The use of one Ampère for one hour.

Ampère-hour meter

An electricity meter that measures and registers the integral, with respect to time, of the current of a circuit in which it is connected.

Apparent Power (volt-amps)

The product of the applied voltage and current in an ac circuit. Apparent power, or volt-amps, is not the true power of the circuit because the power factor is not considered in the calculation.


The data carrying capacity of of a transmission path, measured in bits or bytes per second.


Adjustment of a device so the output is within a specified range for particular values of the input.


1) The ratio of an impressed charge on a conductor to the corresponding change in potential. 2) The ratio of the charge on either conductor of a capacitor to the potential difference between the conductors. 3) The property of being able to collect a charge of electricity.


An electrical device having Capacitance.


1) The negative electrode, that emits electrons or gives off negative ions and toward which positive ions move or collect in a voltaic cell or other such device. 2) The negative pole of a battery.


International Commission on Rules for the Approval of Electrical Equipment A regional, European safety agency in which the United States participates only as an observer.


The capability of a conductor to carry electricity, usually expressed as a percent of the conductivity of a same sized conductor of soft copper


1) A wire or combination of wires suitable for carrying an electrical current. Conductors may be insulated or bare. 2) Any material that allows electrons to flow through it.

Creepage Distance

The shortest distance between two conductors as measured along the device that separates them. Creepage Distance is normally a design parameter of insulators or insulating bushings.

Crest Factor

The ratio of the maximum value to the effective value. It represents the range of input in which a tester maintains linear operation, expressed by a multiple of the full scale value of the range being used. Crest factor = Maximum value/True RMS value For sinusoidal wave; Crest factor = 141/100 = 1.41


1) Direct current. 2) Current that flows in one direction only.

Decibel (dB)

A unit used to express the magnitude of change in level of electric signal or sound intensity. A voltage ratio of 1 to 10 is equal to -20dB, 10 to 1 to 20dB, 100 to 1 to 40dB and 1000 to 1 to 60dB. A power ratio of 10 to 1 is not 20dB, but 10dB, since power(P) is proportional to the square of voltage(V).


Decibels compared to one milliwatt. The higher the dBm, the higher the devices transmit or receive power.


1) Any electrical insulating medium between two conductors. 2) The medium used to provide electrical isolation or separation.

Dielectric Constant

A number that describes the dielectric strength of a material relative to a vacuum, which has a dielectric constant of one.

Dielectric Test

A test that is used to verify an insulation system. A voltage is applied of a specific magnatude for a specific period of time.

Dielectric Withstand

The ability of insulating materials and spacings to withstand specified overvoltages for a specified time (one minute unless otherwise stated) without flashover or puncture.


A two-terminal semiconductor (rectifying) device that exhibits a nonlinear current-voltage characteristic. The function of a diode is to allow current in one direction and to block current in the opposite direction. The terminals of a diode are called the anode and cathode.


The capacitance value of a capacitor of which there appears a potential difference of one volt when it is charged by a quantity of electricity equal to one coulomb.


In ac systems, the rate at which the current changes direction, expressed in hertz (cycles per second); A measure of the number of complete cycles of a wave-form per unit of time.


1. An electrical term meaning to connect to the earth. 2. A conducting connection, whether intentional or accidental by which an electric circuit, or equipment, is connected to the earth or some conducting body that serves in place of the earth.


A sinusoidal component of the voltage that is a multiple of the fundimental wave frequency. Harmonics are primarily the result of the today's modern electronic equipment. Today's electronics are designed to draw current in "pulses" rather than in a smooth, sinusoidal manner as older, non-electronic equipment did. These pulses cause distorted current waveshapes, which in turn cause distortion of the voltage. Current and voltage harmonics can cause such problems as excessive heating of wiring, connections, motors, and transformers and can cause inadvertent tripping of circuit breakers.

Henry (H)

The meter-kilogram-second unit of inductance, equal to the inductance of a circuit in which an electromotive force of one volt is produced by a current in the circuit which varies at the rate of one Ampère per second.

Hertz (Hz)

1) A unit of frequency equal to one cycle per second. 2) In alternating curent, the number of changes of the negative and positive poles per second.




Internation Electrotechnical Commission.


1) The property of a circuit in which a change in current induces an electro motive force. 2) Magnetic component of impedance.

Inrush Current

The initial surge of current experienced before the load restance of impedance increases to its normal operating value.


1) A non-conductive material used on a conductor to separate conducting materials in a circuit. 2) The non-conductive material used in the manufacture of insulated cables.


A prefix indicating one (1) thousand.


1) Apparent Power expressed in Thousand Volt-Amps. 2) Kilovolt Ampère rating designates the output which a transformer can deliver at rated voltage and frequency without exceeding a specified temperature rise.


kVAR is the measure of additional reactive current flow which occurs when the voltage and current flow are not perfectly synchronized or not in phase.


Actual Power expressed in Kilo-Watts (kW).


Kilo Watt Hour, the use of one thousand watts for one hour.


A symbol used to express inductance. The unit of measure is a "Henry".


Light Emitting Diode


A testing device that applies a DC voltage and measures the resistance (in millions of ohms) offered by conductor's or equipment insulation.

Ohm (Ω)

A unit of electrical resistance defined as the resistance of a circuit with a voltage of one volt and a current flow of one Ampère.

Ohm's Law

U=IR; I=U/R; R=U/I; Where U = Voltage impressed on a circuit, I = current flowing in a circuit and R = circuit resistance. Ohm's Law is used for calculating voltage drop, fault current and other characteristics of an electrical circuit.

Peak to Peak

The amplitude of the ac wave form from its positive peak to its negative peak.


Power Factor

Phase Angle

The angular displacement between a current and voltage waveform, measured in degrees or radians.

Phase Rotation

Phase rotation defines the rotation in a Poly-Phase System and is generally stated as "1-2-3", counterclockwise rotation. Utilities in the United States use "A-B-C" to define there respective phase names in place "1-2-3". However some refer to there rotation as A-B-C, A-C-B, or C-B-A counterclockwise, were "A" can replace 1, 2, or 3. Europe adapted R-S-T to define the phase names.


1) The electrical Term used to denote the voltage relationship to a reference potential (+). 2) With regard to Transformers, Polarity is the indication of the direction of the current flow through the high voltage terminals with respect to the direction through the low voltage terminals.

Power Factor

The ratio of energy consumed (watts) versus the product of input voltage (volts) times input current (amps). In other words, power factor is the percentage of energy used compared to the energy flowing through the wires. Adding capacitors to the system changes the inductive effect of the ballast coils, converting a Normal Power Factor (NPF) to a High Power Factor (HPF) system.


Nominal operating limits, specified by the lowest calibration point to the highest calibration point.

Real Power

The average value of the instantaneous product of volts and amps over a fixed period of time in an AC circuit.

Reference range

A specific range of values of an influence quantity within which the transducer complies with the requirements concerning intrinsic errors.

Reference value

A specified single value of an influence quantity at which the transducer complies with the requirements concerning intrinsic errors.

Refererence Conditions

Conditions of use for a transducer prescribed for performance testing, or to ensure valid comparison of results of measurement.

Residual Current

The algebraic sum, in a multi-phase system, of all the line currents.


The opposition to current flow, expressed in ohms.

Root-Mean-Square (RMS)

The effective value of alternating current or voltage. The RMS value equates an AC current or voltage to a DC current or voltage that provides the same power transfer.

Short Circuit

1. A load that occurs when at ungrounded conductor comes into contact with another conductor or grounded object. 2. An abnorman connection of relatively low impedance, whether made intentionally or by accident, between two points of different potential.


THD (%THD, Total Harmonic Distortion) — the contribution of all harmonic frequency currents or voltages to the fundamental current or voltage, expressed as a percentage of the fundamental.

True RMS

Most alternating currents and voltages are expressed in effective values, which are also referred to as RMS (Root-Mean-Square)values. The effective value is the square root of the average of the square of alternating current or voltage values. Many clamp meters with rectifier type circuits have scales that are calibrated in RMS values for AC measurements. But, they actually measure the average value of input voltage or current, assuming the voltage or current to be a sine wave. The conversion factor for a sine wave, which is obtained by dividing the effective value by the average value, is 1.1. These instruments are in error if the input voltage or current has some other shape than a sine wave.


Voltage; Volt.


1) Electrical capacity or electrical load, expressed as Volts*Amps. 2) Volt Ampère rating designates the output which a transformer can deliver at rated voltage and frequency without exceeding a specified temperature rise.


Volt Ampère Reactive. Also see "Reactive Power".


A unit of electromotive force. The electrical potential needed to produce one Ampère of current with a resistance of one ohm.

Voltage Drop

The loss of voltage in a circuit when current flows.


1) With ac measurements, effective power (measured in Watts) equals the product of voltage, current, and power factor (the cosine of the phase angle between the current and the voltage). Watts=E*I *COS(φ). A Watt is a unit of power that considers both volts and amps and is equal to the power in a circuit in which a current of one Ampère flows across a potential difference of one volt. 2) One joule/second.


1) A unit of work equal to the power of one watt operating for one hour. 2) 3600 Joules.


Reactance expressed in Ohms.



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