Welder Feedback

The transformer's rectified output ground lead is probably connected to the welder chassis, which is also probably connected to the 3-ph neutral/ground.

Agreed, some welders have the -ve terminal on the chassis of the welder, some don't, those are able to have the polarity of the output swapped.

You'd find that some times, it isn't just the welder that drops the Earth lead, but could also be 1 or more welders that will have the Earth wire heating problem, as they are acting as the earth return point for the one who dropped their Earth.

Check your power outlet too for heating, as you'd find that the weld currents are more than the Current design spec of the power outlet ;o(

Deleted....by myself, answers were already made!!

You a silly man Andy.

The output connections of any welder should not be connected to the chassis this is a total no no.

What usually happens in large factory's there is a bad habit of connecting the work leads to the metalwork of the building, this is to save running work leads to whatever is being welded,they usually tack a piece of steel rod or cable and clamp from the nearest piece of building structure to the welding table, as the mains supply ground is also connected to the building when a work lead connection goes bad [high resistance]and the welder happens to be touching any part of the object to be welded it will try to feed a couple of hundred amps through a 30 amp earth wire and any or all supply wiring which can prove to be an expensive mistake.

Also with MIG welders the wire can sometimes over run and un spool this will short this can short to the chassis and given above scenario will do the same thing.