Rotary switch voltage rating?

Discussion in 'General Electronics Chat' started by coinmaster, Apr 2, 2016.

  1. coinmaster

    Thread Starter Member

    Dec 24, 2015
    Hi, I need a rotary switch to switch in and out different high voltage circuits.
    The voltages involved are anywhere between -300v and +300v

    I noticed that rotary switches have a voltage rating on them. How can they have a voltage rating when they are effectively a short? There should never be more than 0v between the input and output right?
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    But they aren't always a short ;). When the switch is open you don't want arcing or current leakage between contacts.
  3. coinmaster

    Thread Starter Member

    Dec 24, 2015
    If I have 2 terminals with a high voltage differential while the switch is closed is there a chance of arc or only when it's open?
  4. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    Well you certainly can't get an arc across a short can you?

    For the rotary switch you began asking about you could also get a short between switched lines so with signals of -300 and +300 volts you need 600 volts (minimum!) of isolation rating.
  5. KeepItSimpleStupid

    Distinguished Member

    Mar 4, 2014
    one concept you need to be familiar with is "shorting" and "non-shorting". "Shorting" can mean "make before break" and non-shorting is break before make. the shorting switches were used in audio switching.

    DC, AC and RF have all sorts of different requirements. Some high voltage relays can only switch when they are potential free.

    Materials of the switch has certain breakdown voltages or even bulk-resistivity. Humidity can alter that.

    So, a high voltage can arc while your turning a slow switch.

    The voltage and current are just a part of the problem.
  6. coinmaster

    Thread Starter Member

    Dec 24, 2015
    Well I don't intend to be turning the switch during operation. What I was asking was is there a risk of arcing if there is high voltage potential between the terminals while the switch is fixed in place? Obviously air resistance is much higher than metal but if the thing can arc at a measly 30volts then who knows what can happen at hundreds of volts.
    Last edited: Apr 2, 2016
  7. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    Yes. The higher the voltage the wider the gap needed between terminals.
    The switch manufacturer should know.
  8. MaxHeadRoom


    Jul 18, 2013
    The rating also applies to the insulation value and properties of the switch and the material used.
  9. bertus


    Apr 5, 2008

    As @MaxHeadRoom said , the isolation of the switch is dependend on the used isolation material.
    You will need to have an isolation voltage of at least 600 Volts, as your voltages can be +300, but also -300 Volts.
    A switch rated 1000 Volts would be safe for your application.