How many amps does the oven draw. You size your wire to the amp load. So look to see how many amps the oven draws. It should be on a tag on the oven or in the book that came with the oven. I will bet it is going to be 30-35 amps at 240 volts. Look to make sure. If, and only if it is 30-35 amps at 240 volts then you can use 10 awg wire to hook it up.
