The following definitions apply specifically to surge protective devices (SPD). They are provided for further clarification of the performance specifications in the data sheets.
Crest Value (peak):
The maximum value that a wave, surge, or impulse attains. It is generally associated with the front of a wave.
Clamping Voltage:
The peak voltage across the surge protective device (SPD) measured under the conditions of a specified surge current and waveform. Peak voltage and peak current are not necessarily coincident in time.
Impulse:
A wave (surge) of unidirectional polarity. In testing, the risetime and duration of the impulse are specified, e.g., an 8/20μs impulse, a 10/1000μs impulse.
Maximum Continuous Operating Voltage (MCOV):
The maximum rms value of the power frequency voltage that may be applied continuously between the terminals of the surge protective device.
Nominal System Voltage:
A nominal value assigned to designate a system of a given voltage class, e.g., 120/240 Volt single phase. Note: see ANSI C84.1
Operating Duty Cycle:
One or more operations per unit of time as specified.
Pulse Life:
The number of surges of a specified voltage and current amplitude and waveform that may be applied to a SPD without damaging or changing it. The time interval between surges must be specified.
Maximum Single Impulse Current:
The maximum amplitude of current which may be applied for a single 8/20us impulse.
Power Dissipation:
The power dissipated by a protective device while connected to an AC line of the rated voltage and frequency while no overvoltage condition or surge exists. Steady state power dissipation.
Response Time:
The time domain response of a surge protective device to the front of a voltage waveform depends on the rate-of-rise of the incident wave, the impedance of the surge source and connecting wiring, the effects of protective device reactance, and the response behavior of conducting mechanisms within active suppression elements. In other words, response to the front of a wave can be affected more by the test circuit conditions, including lead inductance, than by the response time of the active suppression element.
Surge:
A transient wave of current, potential, or power in an electric circuit.
Surge Let-Through:
The voltage seen by the protected load, includes the SPD clamp voltage plus the voltage drop in the connecting wires. The part of the surge impulse which passes through the protective device.
Surge Protective Device:
A device for limiting the surge voltage on equipment by discharging or diverting surge current. A SPD should be able to repeatedly perform these functions are specified.
Response Time:
The time required for a device to make the transition from ‘off’ to ‘on or vice versa. Be aware that almost all suppressors using traditional surge suppression technologies are fast enough. For example, the response time of most MOVs is in the nanosecond range, whereas the rise time of a surge is in the microsecond range. This makes the suppressor about a thousand times faster than the surge! Response time is a common specification item, despite having more ‘gee-whiz factor’ than genuine usefulness. Be aware that the speed of electricity is about 6”-8” per nanosecond and that propagation delays through wire are substantially longer than SPD response times.
Voltage-Current (V-I) Characteristics:
The relationship between the suppressed voltage and the magnitude of the surge current which induces this voltage.