Plasma cutter trips GFCI breaker, NOT on same circuit

[DougAustinTX]

I have my trusty Hypertherm 1000 that I use in my detached garage that is about 100' from my house. The power for the garage (and the plasma cutter) comes from a branch circuit on the house's electrical box. For some reason that I can't explain, when I use the plasma cutter, it trips ONE of the GFCI breakers in my house. It does it every time. Has anyone else experienced a GFCI breaker tripping as a result of the plasma cutter being used? I can only guess that there is some sort of pulse making its way back down the feeder circuit.

[jimcolt]

Never heard of this happening.....and it does not occur at my house. I would suspect that there is an issue with either that particular GFCI breaker, or with the wiring to it's outlets. It is likely sensing a current flow through it's ground path.....and perhaps is too sensitive.

Jim Colt

[MoonRise]

GFCI does -not- sense current flow through the ground lines.

It compares the current flowing through the hot and the neutral lines and if there is a current difference of approximately 5 ma (yes, 5/1000 of an amp) then the device trips in approximately 25 msec.

The theory is that if the current flowing 'out' the hot leg and 'back' the neutral leg do not match, then current must be flowing someplace else. And the only other 'someplace else' is assumed to be through the ground line (not the welding 'ground' line aka workclamp line). So the GFCI trips and shuts off the circuit.

As to why your one GFCI back in the house breaker panel trips whenever you use your plasma cutter while in the garage/shop 100 ft away, I have no idea.

Some troubleshooting methods to try and figure out what/why are:

-make sure all electrical connections are properly tightened;

- swap the tripping GFCI breaker with another one. If the problem follows the breaker, then the problem is with the breaker. If the problem stays on the original circuit, then the problem is somewhere in that circuit itself.

GFCI devices can (and do) go 'bad'. They also have varying tolerances for 'standard but non regular' events. I have one GFCI outlet that will trip whenever a bulb on the circuit burns out. So I change the bulb and reset the GFCI.

[jimhoff]

I had this same issue while using my Cutmaster except it was an AFCI--Arc Fault Circuit Interrupter in the breaker panel that was tripping my daughter's Bedroom on the opposite end of the house. I replaced that breaker and the problem disappeared for good. Too sensitive, I think.

[DougAustinTX]

Thanks guys. I will switch out the GF breaker and see what happens.

[MX727]

Thanks guys. I will switch out the GF breaker and see what happens.

Are you sure that it's a GCCI and not an AFCI?

[DougAustinTX]

Are you sure that it's a GCCI and not an AFCI?

It's an old GE GFCI for sure. I had to Google AFCI to even find out what that was. Thanks!

[jkebxjunke]

one thing.. most panel boxes.. the neutral and ground wires are tied on the same buss bar...

[DougAustinTX]

Thanks for the suggestion, and you are right, our house was built in the 80's and the ground and neutrals are all bonded together at the box and that box is grounded with a copper rod. The neutral and ground for the Hypertherm are also bonded at the garage end and there is a long copper ground rod driven into the ground at the corner of the garage and that box is grounded as well.

[A/C Guy]

If the garage is 100' from the house, the ground for that sub panel should have it's own 8' ground rod; per code. The ground should also be connected to your water pipes; per code. Try adding the ground rod and connecting the ground from the sub panel to the water pipes as well, then see if the problem continues. If so, somewhere in the house or the garage, there is probably a neutral and ground wire switched. Then you need to check neutral connections at every outlet and ceiling box and switch box.

[DougAustinTX]

I'll check the wiring. Our plumbing here in Austin is primarily PVC pipe, so we have no iron pipes in this area on houses built in the last 50 years.

[trackbird]

My SW Tig 175 will trip one of two GFCI outlets in my garage when I'm welding thick aluminum on AC. I have all kinds of stuff plugged into both of those outlets (two retractable extension cords which might act as a nice antenna to pick up stray magnetic currents, a tv, stereo, cd player, dvd player (what can I say, I like the garage) and drop lights). I was guessing it was just enough EMI/RFI that it was occasionally tripping the breakers. My tig is wired to the breaker panel with about 4 foot of 8 gauge wire, so it's not a long cable run around the shop. My mig won't trip them and I don't typically trip them when tig welding with DC (or stick welding on DC).