Varistor Selection & Terminology - Nominal vs Rated Voltages

Discussion in 'General Electronics Chat' started by Terroman, Aug 16, 2016.

  1. Terroman

    Thread Starter New Member

    Aug 12, 2016
    I am attempting to stack solid-state relays (VOR2142A8) in order to switch 6000V (3.3mA). The relays are rated for a maximum load of 400V - I have selected these relays because of their lower switching-on time (0.5ms max). For safety operation, I am stacking 20 relays so each will have 300V across its output.

    Vishay's application note on this topic can be viewed at

    To tackle the possible mismatch when switching on, as per the application note, I need to add varistors in parallel with each relay's output. I have selected a varistor (S20K275) which is rated at 275Vac and 350Vdc, so the 400V rating of the relays won't be exceeded. Is this correct, or should I select varistors to have a voltage of 300Vdc?

    Another question that I have is that a similar varistor (14D431K datasheet: ) has multiple rating voltages:

    Max Continuous Voltage RMS: 275V
    Max Continuous VOltage DC: 350V
    Voltage @ 1 mA DC: Minimum 387V, Nominal 430V, Maximum 473V

    Can anybody kindly clarify the difference between the continuous voltage and the Nominal voltage @ 1mA please? (Recall that I have a maximum of 3.3mA at the output of the relays).

    Thank you.