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FAQ02075 of Solid-state Relays FAQ

FAQ No. FAQ02075

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What should be done about surge-absorbing circuits for AC-load Solid-state Relays?


Measures against AC Switching Solid-state Relay Output Noise Surges

1.The Solid-state Relay has a built-in snubber circuit to smooth out a sudden rise in voltage. If there is a large voltage surge in the output-side AC power supply, the snubber circuit will not be sufficient to suppress the surge, and overvoltage will damage the output elements.

2.The following models have a built-in surge-absorbing varistor:
G3NA, G3S, G3PA, G3PB, G3NE, G3J, G3NH, G9H, G3DZ (some models), G3RZ, G3FM

3.Be sure to take measures against surge when switching an inductive load with an Solid-state Relay that does not have a built-in surge-absorbing element. (Refer to the following figure.)

Note:A separate varistor with a surge resistance higher than the built-in varistor must be mounted externally if influence is possible from noise that is not completely absorbed by the built-in varistor (surge resistance: 700 to 1000 A).

Select a surge-absorbing element that meets the conditions in the following table.

VoltageVaristor voltageSurge resistance
100 to 120VAC240 to 270 V1,000 A min.
200 to 240VAC440 to 470 V
380 to 480VAC820 to 1,000 V

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