Help with strange GFI issue

We're currently away for the weekend. Available shore power is 2x 30A with GFI breakers. I have 2x 50A / 125V inlets, so easy to adapt here. A/C has been running since yesterday evening with no issues. The water heater, toaster, coffee maker, etc. all cause no issues. But if I turn the stove on, I get about 5 minutes, then the breaker for that leg trips. I've tried 2 different power posts with the same result.

Ordinarily, I'd suspect an issue with the stove. But if that's the case, why does it take 5 minutes to trip? On top of that, I've used the stove recently with no issues at our home dock, which also has a GFI breaker (50A 125/250V split phase that gets split to my 2x 50A 125V inlets).

For now I'm cooking on generator power, but does anyone have any thoughts on this one? Or an easy way to confirm that the stove isn't having an issue?

What else is running when you are using the stove?

Comodave said:

What else is running when you are using the stove?

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Only other things running on that leg are the battery charger and 2 small fans. At the time of the breaker trip, the meter for that leg was showing 12 amps. The other leg that's had the A/Cs running for hours is showing about 22 amps and that one has been steady with no issues.

Have you plugged into other docks with GFI breakers on the dock?

Is your stove hard-wired or plugged in? As an experiment, is there any chance, with an adapter and heavy extension cord, to plug it directly into the shore power pedestal to see what happens?

The stove is hard wired, so no easy extension cord test. As far as GFI breakers, we have them at our home slip. Last time I used the stove at the dock was a couple of weeks ago and it worked just fine. However, this is the first time I've ever connected to a pair of 30A outlets with GFI breakers. Other GFI docks have all been 50A, so a single double pole breaker. However, this can't be a bonded neutrals issue or anything, as there's no way that only the stove would trip the breaker.

I'm guessing the stove must have some tiny ground leak that's just enough to trip these breakers after a few minutes, but for whatever reason doesn't trip the one at our home dock even though they're all spec-ed at 30ma GFI trip.

The reason I asked if you had used a GFI dock before is that some appliances have the neutral and ground tied together on the appliance which is ok in a house but not on a boat. However that still would not explain why it ran for 5 minutes. It should trip immediately if the ground and neutral are tied together. But you problem is a bit strange...

We both posted at the same time...

I think that maybe just to make absolutely sure you may have to take the stove out and cut the wires. Then check that the ground and neutral do not have any connection in the stove. Or just wait until you get home and make sure it still works at your home dock. Maybe the neutral wire inside the stove has chaffed and is now making intermittent connection to the stove frame/ground.

From what I can find, the trip range for a 30ma GFI breaker is no trip at or below 22.2ma, trip in 0.1 seconds at 30ma. So maybe I've got something like 23ma of leakage where it eventually trips but takes a while?

Once I'm done cooking I'll have to do some testing to confirm if the issue is isolated to a single stove burner or not. I'll also confirm that it still works at our home dock when we get home on Monday. For now, the stove is simmering nicely on generator power, so the only immediate concern is having to listen to the generator on top of the A/Cs for a bit.

The stove in question is the original 1986 vintage Galley Maid Countess 3 burner.

I’m not very electrically inclined at all. However, if I were in your shoes, I would try moving one of your shore power cords to a different pedestal before giving up on the marina.

ScottC said:

I’m not very electrically inclined at all. However, if I were in your shoes, I would try moving one of your shore power cords to a different pedestal before giving up on the marina.

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He said that he had already done that.

ScottC said:

I’m not very electrically inclined at all. However, if I were in your shoes, I would try moving one of your shore power cords to a different pedestal before giving up on the marina.

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That was the first thing I tried. Trip behavior was identical on a different pedestal (with the A/Cs still happily humming away attached to the first pedestal). Turned the stove on high to heat some water, waited about 5 minutes and then "click", breaker tripped.

rslifkin said:

From what I can find, the trip range for a 30ma GFI breaker is no trip at or below 22.2ma, trip in 0.1 seconds at 30ma. So maybe I've got something like 23ma of leakage where it eventually trips but takes a while?

Once I'm done cooking I'll have to do some testing to confirm if the issue is isolated to a single stove burner or not. I'll also confirm that it still works at our home dock when we get home on Monday. For now, the stove is simmering nicely on generator power, so the only immediate concern is having to listen to the generator on top of the A/Cs for a bit.

The stove in question is the original 1986 vintage Galley Maid Countess 3 burner.

Click to expand...

Right now from far away, all I can think of is a wire intermittently making contact with the ground. I would try it at home and see what it does.

Comodave said:

He said that he had already done that.

Click to expand...

Sorry. Missed that!

So once the stove innards get hot it trips? Hummmm.

For about $75 you can get a plug in induction cooktop to tide you over.

I think for now the plan will be to finish cooking, transfer back to shore power, then test each burner individually to see if it's just 1 causing the issue. Depending on what I find, that'll hopefully give me some indication of what to look for as far as an issue with the stove. I'll also re-test when we get back to our home slip on Monday.

I did a little more testing after my corned beef was finished. The issue occurs regardless of which burner is in use. I didn't test 2 at a time though. And it only seems to occur on high. When turned down where the burner cycles on and off, it'll run fine without tripping the breaker.

This sounds a lot more like a load issue than a GFCI issue.

The way thermal breakers (vs magnetic breakers vs leak current circuits) work, they take longer to trip on small overloads than large ones. So, it could easily take a few minutes to pop a breaker if the overload is modest.

I'd get a clamp ammeter and put it around the cord going to the pedestal, near the pedestal. I'll bet it is an overload or darn close.

Then test on the boat end of the cord, again near the main breaker, and again near each device. See if any one of them is misbehaving or if both are.

As for why it doesnt pop on the home dock, it could be breakers with slightly different tolerances or a difference in supplied voltage affecting current draw, e.g. low voltage reduces current draw on resistive loads like many stove tops, but increases it on other types of loads that draw more current do do the same work at a lower voltage.

A load issue was my first thought. However, I know my panel meters work and I was only showing 12 amps when it tripped. The water heater draws just as much on the same leg and that's run without issue. And I know it's not a weak breaker, as both I tried behaved identically.

You are popping the pedestal breaker? Or the boat main? Or the breaker for the branch?

Where is the 12A being measured?

How many watts is the water heater? My 6 gallon is 1500W, 13A-ish at 115V.

15A+12A is 27A, pretty close to 30A. Add in anything else and you could be there. Only way to know is to measure.

Pedestal breaker, 30 amps. Water heater is 1200 watts, so 10 amps. It wasn't on when the breaker popped. Just 1 stove burner, battery charger and a pair of fans, 12 amps according to the meter on the boat panel. The other leg was showing 22 amps with 2 ac units running and had no issues.

Another option is that there is a problem with the neutral and current from one leg is getting returned via the other leg. That might not show up on the supply-side ammeters on your panel -- but would at the 2nd pole of the 2-pole breakers at the pedestal.

Taken together, 12A + 22A = 34A. That is enough for a latent breaker trip.

The thing about GFCI is that it is "immediate". It has to be. Unlike thermal breakers, it isn't designed to allow brief overloads, for example, to start an engine, etc. There isn't a time vs current curve for GFCI breakers the way there is for thermal breakers.

If you were reporting that it was intermittently popping, I'd think maybe there was some worn insulation that was making contact with the metal chassis when the boat moved, or a pot moved, or a cabinet was open or closed, etc. But, if it is a consistent few minutes, that doesn't fit the model for GFCI but does for a thermal breaker.

Obviously, I really don't know. I'm just wildly guessing. But, at least until I learn something else I'm sticking with my recommendation to check with a clamp meter at the pedestal.

If there is GFCI/ELCI/RCD at the pedestal, my view might change (it should pop on an unbalanced load). But, even then, I'd really like to know the current on each leg at the pedestal.

The 12 and 22 are on separate 30a legs. The one with the ACs never tripped. The pedestal breakers are GFI. I'll be able to confirm if the GFI breaker at my home dock has any issue when we get back there on Monday.

Bonded neutrals between the inlets on the boat was my first thought, but that wouldn't explain it only tripping if the stove is in use.

Did you try swapping the two power cords?

Gkesden is probably on the right track. It’s an over loaded neutral. Your boat is set up to use 2 50a out of phase lines that share a single neutral. You have probably found your self on a dock we’re both legs are in phase. So you have 12a + 22a coming in but 34a are departing out the neutral. Electricity is taking the path of less resistance and it sounds like in your case one neutral is less resistant and getting all the current. The breakers on the pedestal are dual pole single throw and they will trip if either power or neutral exceeds 30A

Now a 30a breaker should be good for 35a but If you were really at 12.4 and 22.6 well that’s 35 so trip.

I didn't swap the cords, but I did move one to a different pedestal. I also confirmed again that 15 amps is fine on the problem leg as long as the stove isn't part of that load. When we unplug to leave here, I'll confirm no continuity between the 2 neutrals.

Keep in mind, I have the fairly rare twin 50A / 125V inlets, so a pair of 3 wire cords. Not the 4 wire setup. So there are 2 neutrals from the boat and it shouldn't matter if the sources are in phase or not.

With GFI breakers, I'd expect an immediate trip if any current was taking the wrong neutral, as the breaker would sense the hot to neutral current difference.

My concern is that the stove, or something else, might be returning to the neutral of a leg different than the one supplying it, e.g. the wire got put onto or moved to the wrong bus.

The stove is on a GFCI? If so, is the GFCI, itself, tied to the correct neutral bus, e.g. the same one as the hot that supplies it?

gkesden said:

The stove is on a GFCI? If so, is the GFCI, itself, tied to the correct neutral bus, e.g. the same one as the hot that supplies it?

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No GFI on the stove, just on the pedestal breakers. Main breakers on the boat are not GFI either. I'll definitely need to trace the stove neutral to confirm all is good.

You have stated that at home you have a 50a 125/250 gfi set up that you split into 2 50a legs. That is a 4 wire set up, two power, one neutral and one ground with the powers out of phase. So if you run 12a on L1 and 22a on L2 the neutral only sees 10a.

Now you are on two separate 30a 125v circuits. You have now introduced a second neutral into the system. We don’t know if the two power wires are in phase or out of phase. It’s easy to see how you could have an issue now that doesn’t exist at your home. The 5 minute issue is a challenge but it’s very likely that you are running at the 30a limit and as things heat up the amps are climbing a small amount and this puts you over the limit. So far the only change I see is moving from one neutral to two. This makes me suspicious of the neutral wiring on your boat.