If by some chance and it has happened to me with an old AC welder, fixed leads. Your grounding lead from the welder is not attached firmly to what you are welding and the welding ground path goes back to the grounding conductor in the outlet box and then back to your welder. Bad news. It will overheat that little #12 green wire in your outlet box, or melt the insulation. Now this only happened once to me and it was an electrical extension cord. I just checked both my welders now with an ohmmeter, they are DC and could not get either lead to read to grounded metal. Your results may vary...?
Originally Posted by stoneysstarters
Retired - Journeyman Refrigeration Pipefitter - Master Electrician - Amateur Machinist