Glossary	back to LearnMore
Capacitance The property of a capacitor that determines how much electrical charge can be stored in it for a particular voltage between its terminals. Capacitance resists a change in voltage. Capacitance is measured in Farads.****
Capacitor An electrical component with two conducting plates separated by an insulator, it stores energy in an electric field.
Circuit A collection of electrical and electronic components and paths allowing the flow of electrical current for the purpose of implementing a function, for example, measurement, control. Conversion, processing, communication, regulating, monitoring, etc.
Clamping To forcefully impose a load on an increasing voltage making it much more difficult for the voltage to continue increasing.
Conductor A path designed to allow electrical current to flow easily. It is generally made of a metal, like copper, in the form of a round wire or a rectangular trace or path on a printed wiring board (PWB)/ printed circuit board (PCB). Copper is used because its electrical resistance is low.
Coupling The transfer of energy into an electrical circuit.
Current The flow of electrical charges in a conductor or medium between two points with a voltage between them. Basically it is the amount of charges per second. It is measured in Amperes.**
Energy The ability or capacity to do work or overcome resistance. Energy is measured in Joules.******
Electromagnetic Refers to electric and magnetic fields generated by oscillating electric charges. Oscillating rates of concern for transient overvoltage range from slowly changing DC to 100’s of Kilohertz.
GDT Gas discharge tube (see pg 21)
Ground The earth or an object electrically connected to the earth with a conductor whose voltage drop is considered to be zero. Typically, the connection to earth is made using a metallic rod, stake or pipe. This conducting connection is used to keep the zero or nearly zero earth voltage on conductors connected to it.
Immunity The degree to which the equipment is not affected or influenced by something, i.e., not susceptible; protected from harm.
Impedance The total opposition to the flow of an alternating electrical current of a particular frequency. It is the combination of resistance and reactance (capacitive and/or inductive). It is measured in Ohms.
Impulse A momentary surge of voltage or current in one direction.
Inductance The property of an inductor where a varying electrical current through it creates a varying magnetic field that induces voltage in the inductor or nearby circuits. Inductance resists a change in current. Inductance is measured in Henrys.*****
Inductor An electrical component, typically a group of tightly packed, continuous loops of wire, designed primarily to provide inductance for an electrical circuit. It stores energy in a magnetic field.
Insolation Solar radiation reaching the Earth’s surface.
Insulator A cover or layer designed to prevent the flow of electrical current between separate electrical conductors. It is generally made of a non-metal, like glass, ceramic or plastic, because their electrical resistance is high.
Ionize Become electrically charged or conductive, as a gas due to radiation or high voltage.
Line An electrically conductive path, e.g. wire, copper foil on a printed circuit board.
Line to Ground A mode in which a voltage difference appears between the conductor and ground. Also known as common mode or longitudinal mode.
Line to Line A mode in which a voltage difference appears between two signal or power conductors. Also known as normal mode, transverse mode or differential mode.
Load The device or circuit to which power or a signal is delivered to, whether beneficial or parasitical; in overvoltage protector discussions it is the device or equipment being protected.
Loop A quasi circular figure formed by a line or wire curving back across itself. In as electrical context, a loop is a complete circuit.
Mode Refers to the way a signal is, acts or appears in a circuit, for example Line to Gnd or Line to Line.
MOV Metal oxide varistor (see pg 21)
Overvoltage A voltage exceeding the normal, intended or allowed maximum voltage.
Parallel In a simple circuit, refers to a component with the same voltage as the load but a separate current, i.e., in parallel with the load.
Power The rate at which energy is transformed. Power is measured in Watts.******
Reactance The opposition to the flow of an alternating electrical current of a particular frequency due to capacitance and or inductance.
Resistance The property of a conductor or medium which opposes (resists) the flow of electrical current resulting in the generation of heat in the conducting material. It is measured in Ohms.***
Resistor An electrical component providing a specific amount of resistance and a defined power rating in Watts.******
Series In a simple circuit, refers to a component with the same current as the load but a separate voltage, i.e., in series with the load.
Shunt Connected so as to divert part of the load current; connected in parallel with the load.
Spike A short-lived, rapid, sporadic voltage variation.
Surge A sudden, rapid increase of electrical voltage or current in a circuit.
Susceptibility The degree to which the equipment is affected or influenced by something, i.e., how sensitive it is; vulnerable to harm.
Switch An electrical device used to open or close a circuit path.
Transient Temporary, passing quickly, not permanent, momentary.
TVSD Transient voltage suppession diode (see pg 22)
Voltage The force or electrical pressure that causes electrical charge to flow. It is measured in Volts.*
*Alessandro Volta 1745-1827, Italian Physicist
**Andre Ampere 1775-1836, French Physicist
***Georg Ohm 1789-1854, German Physicist
****Michael Faraday 1791-1867, English Scientist
*****Joseph Henry 1797-1878, U.S. Physicist
******James Joule 1818-1889, English Physicist
*******James Watt 1736-1819, Scottish Engineer