HI to size wire and breakers you multiply your rating by 1.25% because you never exceed 80 rating on your feeders this is so you dont overheat your wires. #8 wire is rated at 55 amps and #6 wire is rated at 75 amps for your welder I would use # 6 wire minimum and a 50 amp breaker. I am a licensed elfor 32 years good luck.
