Question about GFI breakers


Old 05-11-06, 12:52 PM
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Question about GFI breakers

I have had a couple of problems on an RV under the following conditions. The RV has a 30 amp shoreline that goes to a breaker box with (2) 15 amp gfi breakers. Even without a load on any circuit in the RV, if the shoreline is supplied with voltage from another gfi breaker(the input is also protected by a gfi breaker) then it trips one of the breakers. Sometimes it will trip the shoreline breaker, sometimes it will trip the supply breaker. I have been told gfi breakers do not like to cooperate in this configuration. If I replace either the supply breaker or shoreline breaker with same size non-gfi breaker, everything runs fine. The reason I am asking is I have beeen unable to find anything to support the claim that two gfi breakers in-line could be a possible problem. Any help in this matter would be greatly appreciated.

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Old 05-11-06, 01:13 PM
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Sorry, two GFCI breakers in series is not a problem.
Old 05-11-06, 01:17 PM
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You probably have a ground fault somewhere in the system. GFCI breakers in series are not usually a problem. Is this a system that has worked before and now suddenly doesn't work or is this a new installation that doesn't work?
Old 05-11-06, 02:05 PM
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This is a new installation that does not work. I have checked all circuits in the RV for ground faults and found none. I had this happen to me about 6 or 7 years ago on a 120VAC HVAC unit that was installed in a RV. The HVAC unit had a gfi breaker internally with the inpout comming from a 20 amp gfi breaker in breaker box. The system failed continually and I was told at that time about gfi in series not working by the HVAC manufacturer. I have recently run into problem again on this new project. Is it possible a voltage drop across the four connections required for (2) gfi in series in affecting the current. I know it only take a 5 milliamp difference to trip breaker. I ill check for ground faults in the supply side. Thanks for the replies.
Old 05-17-06, 08:11 AM
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Still have found no ground faults in either system. Has anyone else heard of or expeirenced a problem like this. I have changed the RV breakers to non gfi for the time being and it is still working good. I even got new gfi breakers just to make sure i didn't have some bad out of the box ones the first time. I am stumped. Any ideas would be greatly appreciated.
Old 05-17-06, 05:13 PM
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Could you sort of map out in words where all these breakers are and where the input one is and what IT'S amp rating is?

Could the input line and the outgoing load wires be reversed according to the main plug-in cord, or something?

I am not quite following your story about the "shoreline". (Not into RV lingo, I guess). Do you have an RV with a panel box in the RV and then you plug a main power cord into some stationary park pedestal that has a GFCI in it? Is that it? If so...that is what my second paragraph is about.
Old 05-17-06, 09:22 PM
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Normally one GFI breaker downstream from another GFI breaker will not cause either of them to trip. However, when ground fault problems do happen, it may result in one or the other breaker tripping, or both. And it could randomly very at each incident. This would be especially common when the fault current is low and very close to the tripping threshold of the breakers. GFI breakers for people protection should have a trip point somewhere between 2 milliamps and 6 milliamps. A high ground fault current (for example 2 amps) should usually trip both together, whereas a low ground fault current (for example 10 milliamps) is likely to trip just one breaker.

There are many possible causes for non-obvious GFI trips. A connection somewhere between the ground wire and the neutral wire could cause one or the other to trip. An excessive amount of total circuit length (adding up each branch) could have enough circuit capacitance to cause a trip.

The fact that you have the problem only when there are 2 GFI breakers, but never when there is just 1 GFI breaker, is very peculiar. I might suspect that the 2nd GFI breaker, or its enclosure, has been miswired, possibly feeding that GFI breaker backwards.

Also, a combination of conditions could cause problems to accumulate. If wiring capacitance is high, but not quite high enough to trip a GFI breaker, it could still contribute to another cause of some fault current. The 2nd GFI breaker itself may be somehow a cause of the problem.

If you already have other GFI breaker known to work correctly, you might substitute these, particularly for the 2nd breaker, to see if it's just a leaky breaker.

Another test to be done VERY CAREFULLY is to power the circuit with the ground wire not connected. Remember this is ONLY for testing purpose and absolutely should NOT be left operating this way under any circumstances. Also, no children should be around, and no one should be near the RV whatsoever. If things "work" with the ground wire (between the 2 GFI breakers) not connected, you probably have a wiring problem or a leaky breaker.
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