In article ,
says...
What is the common welder size? (in amps?)

I noticed that no one has mentioned that it depends on the type of welder
you end up with.

For example, a Lincoln AC 225 or AC/DC 225/125 takes a 50 amp outlet. I
think my SP-170T (an excellent Lincoln MIG welder) calls for 30 amps but I'm
not sure because I plugged it into the outlet that was already there for my
old AC 225.

But now I also have an old IdealArc 250/250 which we use for arc and TIG
welding and it calls for 90 Amps! We're able to use it in the 50 Amp outlet
but only at about half capacity. You probably think it unlikely that you
would ever have anything this large (I certainly did!) but at $500 it was a
lot cheaper than a newer inverter-based TIG welder that uses less current so
it's worth considering. :-) You'd be surprised what kind of deals you can
get if you go to a few auctions.

Good advice. I've purchased several TIG welders at auction
over the past 25 years and have never paid more than $400
or so. The latest is an Airco square wave that was only a
few years old when I got it.

These machines typically require a 100A circuit to run at
full capacity. As Keith says, you can do most things with a
smaller feed, but if you want to weld 1/4"+ aluminum you'll
want the 100A circuit.

I'd at least run wire large enough to upgrade to 100A in
the future, even if you install a smaller breaker now.
(Make sure the breaker lugs will handle the larger wire.)
There are special exceptions that allow the use of smaller
than normal conductors for welders, but the actual
selection depends on the duty cycle of the welder. Unless
the length of the run is very long, I'd just run wire with
100A ampacity.

Ned Simmons