wow that's funny as i thought my post would be like the "last word" however there are two more pages afterwards. y'arr.
to the guy from illinois, yeah, check your local codes, however this whole thing is bootlegged in so isn't getting inspected. as for illinois being the better code i seriously doubt it. it is my understanding that for years and still currently, the city of Chicago has it's own code stating that Romex shall NOT be used in a house and that they are all wired in CONDUIT.
as for this welder thing. code or no code, one thing ALWAYS takes precidence, well, actually, this IS in the NEC, i just aint gonna take the time to find it, and that is this: Manufactures instructions must be followed. period.
also, even if you don't have aluminum service entrance conductors going into your panel, i will bet you my bottom dollar that the Power Companys service drop wires from the transformer are AL. all you have to do is see if the wires coming down from the sky are smaller, MUCH smaller, than the ones after the butt splice to the wires coming out of the service mast. (even if they are both aluminum they are)
just fyi, i have an arc welder. stick, right. and i have used it hard wired into a 30A 2 pole breaker and used it to build my truck chassis and it never tripped. however i never did use an amp meter on it to see if it was getting hot or not. i think in your case you will be okay. just don't quote me if your house burns down. hahahaha. one thing that has always puzzled me is why you have to have a certain amperage circuit, say 20 amps, and when you get into the fixture or appliance you have like 16 ga wire or 18 ga. it would figure those things wouldn't need any more than the internal wires inside are good for, wouldn't it? peace out