Originally Posted by
Rambozo
Yes, if you wire a 30 amp circuit you can usually use 10 ga. Check your local code for the specifics on what is required in your area.
Yes, if you want a 40 amp breaker, you will need 8 ga. minimum.
The chart posted was the NEC section on derating wire for welders with limited duty cycles. It only applies to extension and input cords, not building wiring, as Sportbike mentioned. That chart is why the machine only has a 12 ga. input cord, even though it can draw 31 amps. Basically you size the wire to control heat. In a nutshell, because welders can't run at full power constantly, they give the wire time to cool off, so a smaller wire can be used. What it means for you is that you can use slightly smaller extension cords than the amp draw, and distance, would normally dictate.