As Gigs said, size the breaker for the wire. A 40 amp breaker should be
attached to 8 gauge wire, as I recall it. If the wire is 10 ga or less,
replace it with 8 gauge.

40 amps or 50 amps at 220 volts sounds right for a typical stick welder.
Mine is wired to a 50 amp breaker.

Richard



Gigs wrote:
You should size the breaker for the wire, not for the load.

Size the wire for the load.