Tripping a GFCI receptacle

[Spencer]

I can't get my Spectrum 125C plasma cutter to start cutting without tripping the GFCI receptacle that it is plugged into. I can turn the unit on and everything will be fine until I use the trigger to try and initiate the arc. I used a Thermal Dynamics Drag-Gun for the last 7 years on GFCI's without any problems. If I find a normal 115-volt receptacle the Spectrum will work, but it is very difficult to find non-GFCI receptacle for me to plug it into. The majority of my work is done in new restaurants. The NEC requires that all 115-volt receptacles in a commercial kitchen be GFCI. Do I have a bad 125C or are they designed to not work in GFCI's.

Also the owners manual states that I am supposed to be able to re-initiate the arc during the postflow period. If I try to do that there is a pause, and then the arc is initiated. My old TD Drag-Gun would instantly re-initiate the arc. Again, do I have a bad unit or is this the way Miller designed them?

Thanks, Spence

[hankj]

Somehow, there is a path for current flow to someplace other than the neutral wire being established when you pull the trigger. A GFCI works by sensing the balance in current flow between the conductors. If it's tripping, it is not seeing as much coming back as it sees going in. I'd suspect the machine.

Hank

[INTP]

You could test hankj's scenario with a clamp type ammeter. You'll probably have to make a short lead for this, so you can clamp the individual wires. The GFCI trips if there is inductance around the black and white wires together. So if you clamp just these two wires, and you read current, something is up with the unit. The idea is that the current in the black wire is offset by the current in the white wire, unless there is current flowing elsewhere.

You can also clamp just the ground wire, because that's most likely to be the alternate path for the current. If you read anything at all in the ground, then, again, there's something up with the unit.

If either of these tests shows a problem, be sure to get the unit serviced, since it's a shock hazard.


I don't know if this has anything to do with your situation, but I used to have a problem with my 180SD tripping a GFCI. The 180SD is 240V, of course, but the high frequency was causing the GFCI that my 120V radio was plugged into to trip. I replaced just that GFCI with a better one and the problem stopped.