In article 1119797867.565455.246460
@g14g2000cwa.googlegroups.com, says...
You should size the breaker for the wire, not for the load.

Size the wire for the load.


Yes, *but*, the NEC allows the conductors supplying a
welder to carry more than their normal rated ampacity. For
example, if we assume the welder in question with a primary
rated current of 41 amps has a 20% duty cycle rating, then
the supply conductors need only have a rated ampacity of
18.5A. So you could conceivably have an installation with
14ga wire protected by a 40A breaker feeding the welder.

There are other things to consider (including whether this
sort of thing is a good idea in a residential setting in
the first place), but the provisions are there in the NEC
if you care to take the time to understand them.

Ned Simmons