Can you install a 20amp switch on a 300-500v cable

Well this would depend on the current carrying capacity of the cable you would need to check the rating in amps that the cable can carry?

Whats the size of the cable cores? what are you trying to achieve? Why are you asking this rather than getting someone in to do whatever you want doing? I would suggest by your question you leave electrics well alone.

Hi Vanessa Your question is very wrong asked for us. This is just an information so please don't follow it or apply it unless you know what your doing. In simple words: 1. how much power (watt) does that grid switch operates (in your case the appliance power) 2. what cable size do you need for that power taken by the switch 3. select the braker (amps) to protect the chosen cable It's not important how many volts (v) can carry a cable is important how many amps can carry a cable as from there can start a fire. There is a lot of theory to fallow on this topic but it's easiest for both of us if you just call an electrician to help you with your project and ask him on the spot about your curiosity.

Switch need to be 415 volt rated however you wouldnt use a 20 amp grid switch for 415 volt switching unless its switching a contactor, etc with a single phase coil.