Rotary switch voltage rating?

coinmaster

Joined Dec 24, 2015
502
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?

Alec_t

Joined Sep 17, 2013
14,234
How can they have a voltage rating when they are effectively a short?
But they aren't always a short . When the switch is open you don't want arcing or current leakage between contacts.

coinmaster

Joined Dec 24, 2015
502
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?

ErnieM

Joined Apr 24, 2011
8,376
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?
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.

KeepItSimpleStupid

Joined Mar 4, 2014
5,088
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.

coinmaster

Joined Dec 24, 2015
502
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:

Alec_t

Joined Sep 17, 2013
14,234
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?
Yes. The higher the voltage the wider the gap needed between terminals.
who knows what can happen at hundreds of volts
The switch manufacturer should know.

Joined Jul 18, 2013
28,533
The rating also applies to the insulation value and properties of the switch and the material used.
Max.

bertus

Joined Apr 5, 2008
22,264
Hello,

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.

Bertus