Transformer wiring for a 240 volt arc welder?

I know this sounds stupid but several weeks ago I noticed my 3 pin 240 volt cable on my 140 amp arc welder was frayed, I removed the cable, and placed a bit of tape marked as active, on the terminal block from where the active and neutral came from, I got too busy to finish it, and consequently it has since fallen off, now I'm not sure which side was active, this has 2 very heavy wires into the terminal block which I ume come from the transformer, and the earth to the welder frame, if I get these wires transposed what would be the results, I would have to drill out numerous rivets to see the internals and transformer and vitually dismantle the whole thing, any suggestions appreciated.