Having trouble understanding GFCI problem

[mikestock]

I have my MH in a storage lot with low capacity electrical hookup for battery charging.

Three of us are hooked into one box. After the initial bulk charge for a few seconds mine drops off to below 50 watts. The other two are pulling 95 and 325 watts respectively. I even tried running the generator while attaching the plug to avoid the charger going into bulk charge.

Any two of us are OK but the third knocks out the 20 amp GFIC. Doesn't matter which is the third, it trips.

I know we are in no way approaching 20 amps, even when first plugged in.

This station plus one other is fed by a 30 amp breaker, but it never opens.

I'm asking the owner to get the GFIC breaker checked but he said it was checked about a month ago when someone else complained. He is a hard headed individual who knows it all.

I still think something is going wrong with the GFIC breaker but I'm no expert. May go buy one myself and changing it out. Easy way out if this is the problem.

[mikestock]

LittleBill wrote:
can you just add another gfci outlet?

I think that's just what I will do unless I can move to another spot with access to another box.

[pianotuna]

Hi,

Tonight I'm having to use the generator as the GFCI is popping due to wet snow. What a pain!

[DrewE]

wnjj wrote:

DrewE wrote:

I don't think code ever allows 20A receptacles to be on a circuit with 30A overcurrent protection, GFCI or none, multiple receptacles or not. You would need to have a 20A breaker or fuse to limit the current to the receptacle. The only case I'm aware of where you may have receptacles that are rated for less current than the breaker or fuse is that it's permitted to have more than one 15A receptacle on a 20A circuit, but that's a special case in the code (and a very commonly used one at that).

I read the various posts to mean there's a 30A "main" breaker upstream feeding more than one box but with each of the boxes having a 20A GFCI breaker for the 4 local receptacles.

Re-reading the posts, I believe you are correct and I misunderstood the setup. In this case, I'm glad that I was getting it wrong.

[Hurricaner]

The problem is three battery chargers plugged into one GFIC. One charger is fine and two will still be OK but the third adds up to enough ground leakage that the GFIC trips. There is no way around this except adding a parallel GFIC receptacle to split up the chargers.
All switching power supplies(modernconverters, IE battery chargers) leak a small amount of current to ground. This is usually not enough to trip a GFIC but if you have several the additive effect will.

Sam

[wa8yxm]

I have owned several devices (IE: My Lady's Hair Dryer) with GFCI plugs. they are 2 prong devices, no ground.

HOWEVER I would ground the RV's chassis, even if .. Well I have a LONG (like 3 feet) Screwdriver with some #10 wire clamped just below the handle.. Where the A/C Drips. I shove it in the ground when I feel the need.

[Harvard]

road-runner wrote:

Harvard wrote:

road-runner wrote:

Harvard wrote:
Personally, I would suspect the GCFI to be faulty IF IT DID NOT trip with the 3 RVs. But then that is just me and my stray capacitance theories. 🙂

Just for debate's sake, if the stray capacitance were balanced, there would be equal leakage between hot-ground and neutral-ground. Exaggerated, you could leak a full amp on both sides and not trip the GFCI. As I type this, I'm agreeing with you more and more, because I've never seen the leakage to be exactly equal, with more being ground-neutral than ground-hot. So agreeing with you, I'd place my bets on the imbalance being heavier between neutral and ground.

Yes, the stray C is balanced BUT the VAC across the two is very different. The HOT wire is 120 VAC to GROUND while the NEUTRAL is almost 0.0 VAC to GROUND. Which one is going to have the most leakage current? The HOT, IMO.

I flip sides on this issue depending on how I look at it. Here's what drives the guess that the neutral-ground leakage is greater: If the leakage was perfectly balanced, the ungrounded chassis would float at half the line voltage. I've measured the float voltage of 5 or so ungrounded RVs, and in every case, the chassis float voltage has been less than half, typically around 40 volts. That tells me that the ground-neutral coupling is greater. But then there's the direct to ground leakage through jacks and tires, so it's probably not as simple as I'd like it to be.

I do not think it would be outrageous to think that the added loading to your observed NEUTRAL side is the result of the in parallel RV CHASSIS footprint being one C plate in proximity to an equally sized EARTH GROUND plate.

[wnjj]

DrewE wrote:

mikestock wrote:

DrewE wrote:
(I'm wondering why this place has 20A receptacles protected by a 30A breaker, but as I'm not the local electrical inspector I guess it's really none of my business.)

The 30 amp breaker feeds at least 3 boxes. All GFCI breakers on the shelf at Lowes ar either 15 or 20 amps. 30 amp GFCI's may be available but are apparently not too common.

30A GFCI breakers are indeed available and not too hard to find, though they aren't generally at Home Depot and similar stores.

30A GFCI RV receptacles are not available, or at least I've never seen nor heard of them.

I don't think code ever allows 20A receptacles to be on a circuit with 30A overcurrent protection, GFCI or none, multiple receptacles or not. You would need to have a 20A breaker or fuse to limit the current to the receptacle. The only case I'm aware of where you may have receptacles that are rated for less current than the breaker or fuse is that it's permitted to have more than one 15A receptacle on a 20A circuit, but that's a special case in the code (and a very commonly used one at that).

I read the various posts to mean there's a 30A "main" breaker upstream feeding more than one box but with each of the boxes having a 20A GFCI breaker for the 4 local receptacles.

[DrewE]

mikestock wrote:

DrewE wrote:
(I'm wondering why this place has 20A receptacles protected by a 30A breaker, but as I'm not the local electrical inspector I guess it's really none of my business.)

The 30 amp breaker feeds at least 3 boxes. All GFCI breakers on the shelf at Lowes ar either 15 or 20 amps. 30 amp GFCI's may be available but are apparently not too common.

30A GFCI breakers are indeed available and not too hard to find, though they aren't generally at Home Depot and similar stores.

30A GFCI RV receptacles are not available, or at least I've never seen nor heard of them.

I don't think code ever allows 20A receptacles to be on a circuit with 30A overcurrent protection, GFCI or none, multiple receptacles or not. You would need to have a 20A breaker or fuse to limit the current to the receptacle. The only case I'm aware of where you may have receptacles that are rated for less current than the breaker or fuse is that it's permitted to have more than one 15A receptacle on a 20A circuit, but that's a special case in the code (and a very commonly used one at that).

[road-runner]

Harvard wrote:

road-runner wrote:

Harvard wrote:
Personally, I would suspect the GCFI to be faulty IF IT DID NOT trip with the 3 RVs. But then that is just me and my stray capacitance theories. 🙂

Just for debate's sake, if the stray capacitance were balanced, there would be equal leakage between hot-ground and neutral-ground. Exaggerated, you could leak a full amp on both sides and not trip the GFCI. As I type this, I'm agreeing with you more and more, because I've never seen the leakage to be exactly equal, with more being ground-neutral than ground-hot. So agreeing with you, I'd place my bets on the imbalance being heavier between neutral and ground.

Yes, the stray C is balanced BUT the VAC across the two is very different. The HOT wire is 120 VAC to GROUND while the NEUTRAL is almost 0.0 VAC to GROUND. Which one is going to have the most leakage current? The HOT, IMO.

I flip sides on this issue depending on how I look at it. Here's what drives the guess that the neutral-ground leakage is greater: If the leakage was perfectly balanced, the ungrounded chassis would float at half the line voltage. I've measured the float voltage of 5 or so ungrounded RVs, and in every case, the chassis float voltage has been less than half, typically around 40 volts. That tells me that the ground-neutral coupling is greater. But then there's the direct to ground leakage through jacks and tires, so it's probably not as simple as I'd like it to be.

[LittleBill]

can you just add another gfci outlet?

[mikestock]

DrewE wrote:
(I'm wondering why this place has 20A receptacles protected by a 30A breaker, but as I'm not the local electrical inspector I guess it's really none of my business.)

The 30 amp breaker feeds at least 3 boxes. All GFCI breakers on the shelf at Lowes ar either 15 or 20 amps. 30 amp GFCI's may be available but are apparently not too common.

[ScottG]

drsteve wrote:

Camreal wrote:
Replace it with a standard plug. You have 2 more circuit breakers in line for protection and as said we got away without using them for years.

Bad idea. A circuit breaker and a GFCI protect against different hazards. A ground fault will not trip a traditional circuit breaker, and a ground fault can kill you.

And we didn't get away without using them. People died - many of them children.


I can't help with the OP's dilemma but I saw a similar issue at a construction equipment shop.

It seems they could plug in one or the other dump truck's block heater but not both - IT WAS NOT AN OVERLOADING ISSUE.
Any time they were both plugged in the GFCI would trip during the night.
Finally had to run a new circuit.

[joshuajim]

pianotuna wrote:

We got along just fine for a hundred years without GFCI.

After doing some research, I discovered that all the people that died from electrocution failed to provide input 😉

[DrewE]

mikestock wrote:
All I really want to know and it's still not quite clear: Will a GFCI breaker trip, strictly due to over current and is there an obvious malfunction with the breaker, considering that any on of the three units will cause the trip?

Pianotuna's idea of stacking one RV off the other may be interesting. We don't have any outside outlets but I may try plugging my nextdoor neighbor into one of my receptacles to see what happens.

A GFCI breaker (as in one in a circuit breaker box/load panel) is both a GFCI and a circuit breaker, and so it will trip from either overcurrent or from a current imbalance between the hot and neutral lines, which indicates leakage somewhere.

A GFCI receptacle is not a circuit breaker, and will not trip due to overcurrent...but it should of course be protected by a circuit breaker upstream.

The breaker is not tripping due to overcurrent; you're consuming very much less than its rated capacity. Logically, it must be tripping due to it thinking there's a ground fault, apparently due to accumulated leakage current. You might be able to prevent the tripping by shutting off the circuit breakers for all. the circuits in the RVs you aren't actually using--which presumably would be most or all of them other than the converter circuits.

(I'm wondering why this place has 20A receptacles protected by a 30A breaker, but as I'm not the local electrical inspector I guess it's really none of my business.)