To avoid both undesirable scenarios, (and assuming the welder REALLY is 30A max (sometimes welders will have a high inrush current when using posi-start or other enhanced cold-start logic)) - what do folks think of him making an extension cord with whatever plug he needs on each end - that way he doesn't have to modify his welder and when he moves out, he takes his 30A to 50A extension cord with him and the next homeowner is left with a 30A plug and a 30A breaker - this seems to be the best of both worlds. Again, disclaimer, I ask WHY did Miller put a more expensive 50A plug on a machine if it "only draws" 30A. I suspect that will be the driving concern: as it is possible that under certain settings/conditions there is a greater inrush current....
+1 on contacting Miller about this issue - they will be able to help on multiple fronts.
Last edited by alaskanengineer; 01-23-2012 at 12:57 PM.
Reason: minor grammar edit - - makes more sense now