If you have to ask here, you shouldn't be trying to wire in a 20A compressor. You will require a special circuit for the voltage and current with an independent breaker.
Check your local code for the wire size or talk to a qualified electrician.
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Normally a AWG #10 wire on a 30 amp breaker will suffice. But check the compressor owners manual to make sure.
The size of conductor needed will be a #14. It should be copper and have an insulation factor of 90 degrees C. The fact that it is a three phase load does not enter into the calculation of the wire size.
A 10 mm cable is most commonly used for a 500 KVA transformer, 240 volt, 3 phrase. The size of the wire that is used in a transformer is based on the voltage.
AWG #3 copper.
480 Volt
As with any electrical installation, the wire size used depends on the expected maximum current the wire will carry. That cannot be determined by voltage alone.