Test and Tagging Welders -Guarding Against Inadvertant Damage To Your PAT

With welders, the input lead circuitry typically includes radio frequency interference (RFI) filtering (a ladder of resistors, inductors and capacitors rated at the input voltage 240VAC 50Hz) and this is usually un-switched. Un-switched means that if the supply lead is powered (switched on and providing 240VA 50Hz) from the general power outlet at the wall, the RFI circuit is powered, drawing a small current. 

It also means that when you conduct a run test on the unit, with the portable appliance tester, without it being switched on at the unit, the run test could pass even though nothing else is powered - making the test invalid.

Once the welder is switched on, the run test could fail because of an earth leakage elsewhere in the unit. The threshold earth leakage test current is usually signaled by the portable appliance tester at 6 milli-Amperes or above. 

A common source of earth leakage is from the gas valve in MIG welders so you wont get the leakage until the valve is activated.

Any work done to repair the welder, should have the welder re certified for electrical safety. Normally, for metal cased welders, this may entail proper electrical bonding of the case be accomplished and a Class I test carried out.

If you are doing a run test on a welder with a portable appliance tester that is looking for an earth leakage current, consider connecting the portable appliance tester to a portable 10mA RCBO to prevent internal damage to the portable appliance tester if the earth leakage current is excessive.