High-frequency ground and GFI breaker

[MuttonHawg]

Does anybody know if using the HF ground terminal on the PP256 would cause any issues with a GFI breaker? I'd think that for it to be able to affect the HF noise coming from the machine, there would have to be something flowing through that lead, (whereas normal ground is a safety path that shouldn't normally carry any current). I'm also not sure if the GFI breaker would be sensitive to current flow at that high a frequency anyway. It would be unfortunate if using the HF ground would cause the breaker to constantly trip.

[zoama]

The ground bolt on all these machines is a chassis ground and just gives you a connection point for a shorter ground path.

[Rambozo]

Does anybody know if using the HF ground terminal on the PP256 would cause any issues with a GFI breaker? I'd think that for it to be able to affect the HF noise coming from the machine, there would have to be something flowing through that lead, (whereas normal ground is a safety path that shouldn't normally carry any current). I'm also not sure if the GFI breaker would be sensitive to current flow at that high a frequency anyway. It would be unfortunate if using the HF ground would cause the breaker to constantly trip.

Something like a variable frequency welder might cause nuisance trips. Please report back on how that works for you. When they first came out, all kinds of machinery would trip them. I know they are much better now, but an inverter welder might be pushing it.
The separate ground will not cause a trip, but might disable part of the GFCI system as the breaker will not be able to test for current leakage to ground.

[zoama]

Something like a variable frequency welder might cause nuisance trips. Please report back on how that works for you. When they first came out, all kinds of machinery would trip them. I know they are much better now, but an inverter welder might be pushing it.
The separate ground will not cause a trip, but might disable part of the GFCI system as the breaker will not be able to test for current leakage to ground.

It's not a seperate ground it's a bonded ground.

[Rambozo]

It's not a seperate ground it's a bonded ground.

True, probably not the best wording on my part. Let's say alternate ground path. The net result is that the GFCI will no longer have the only ground path to measure current on. So you could have some current leaking to the chassis and going through the ground attached to the ground point on the back and the GFCI will not trip, because it will see no current through it's ground line. Not anything I would mind, but something to be aware of.

[zoama]

True, probably not the best wording on my part. Let's say alternate ground path. The net result is that the GFCI will no longer have the only ground path to measure current on. So you could have some current leaking to the chassis and going through the ground attached to the ground point on the back and the GFCI will not trip, because it will see no current through it's ground line. Not anything I would mind, but something to be aware of.

I see your point.

[MuttonHawg]

True, probably not the best wording on my part. Let's say alternate ground path. The net result is that the GFCI will no longer have the only ground path to measure current on. So you could have some current leaking to the chassis and going through the ground attached to the ground point on the back and the GFCI will not trip, because it will see no current through it's ground line. Not anything I would mind, but something to be aware of.

Actually, based on how I understand the way GFCIs work, I was concerned about the opposite case - leakage out the chassis ground that was not problematic, but WOULD cause the GFCI to trip.

As I understand it (based on web research, for instance: here), a GFCI basically sums up all the current through (in the case of a double pole breaker) both hot lines and the neutral, and that should sum to zero. If any current is going through the ground (which should not happen under normal circumstances), then the sum will be non-zero and it will trip the breaker because of a ground fault. If the HF chassis ground ever carries enough current at a frequency that the GFCI breaker is sensitive to, I could see it potentially causing a problem.

But Rambozo is right - the proof is in the pudding. Whenever I eventually get the PP256 I'm lusting over, I'll try it out and let you know. In the meantime, I think I will swap out my 50A breaker for a GFCI breaker, because the outlet is in my garage and therefore technically should be GFCI protected. I hope it doesn't cause problems in the future, though, because 2-pole GFCI breakers ain't cheap.

[Rambozo]

Actually, based on how I understand the way GFCIs work, I was concerned about the opposite case - leakage out the chassis ground that was not problematic, but WOULD cause the GFCI to trip.

As I understand it (based on web research, for instance: here), a GFCI basically sums up all the current through (in the case of a double pole breaker) both hot lines and the neutral, and that should sum to zero. If any current is going through the ground (which should not happen under normal circumstances), then the sum will be non-zero and it will trip the breaker because of a ground fault. If the HF chassis ground ever carries enough current at a frequency that the GFCI breaker is sensitive to, I could see it potentially causing a problem.

But Rambozo is right - the proof is in the pudding. Whenever I eventually get the PP256 I'm lusting over, I'll try it out and let you know. In the meantime, I think I will swap out my 50A breaker for a GFCI breaker, because the outlet is in my garage and therefore technically should be GFCI protected. I hope it doesn't cause problems in the future, though, because 2-pole GFCI breakers ain't cheap.

You are right, that could be a problem. I've only played with older versions of single pole units and know whats inside them. I know it is required that the ground and neutral not be bonded anywhere down stream from them or they will trip even with no load connected. I can see having GFCI for 120V garage outlets for portable power tools, but I would not want them for a welder or any large machinery.

And BTW: Since your welder is isolated from the input, it will still shock you, GFCI or not. Just so you are aware of that.