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
    12
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    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 http://www.vishay.com/docs/83602/appnote67.pdf

    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: https://www.bourns.com/data/global/pdfs/MOV14D.pdf ) 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.
     
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