Originally Posted by scotzz
Actually I will be using a welder that draws 20A. Why is this any different than an appliance/TV/lamp/etc that draws only a few amps from a 120v, 15A line?
The breaker protects the wire.
The feed cord on your 20 Amp welder will be #12 wire. It will not be protected with a 30 Amp breaker and will create a hazard even if your extension cord is #10.