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Old 09-14-2013, 09:02 AM   #1
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How to solve tripping GFCI

My restored old Tradewind trips GFCI's if the shore power cable is plugged in to them. I know that this is a fairly common problem.

From what I read, the usual culprit is a ground rail that's bonded to the neutral bus. My problem persists, however, when all of the branch circuit breakers are turned off. From this I figure that the issue is somewhere "central" in the vicinity of the inverter/charger or the batteries.

Anyway, here's the question: Assuming that the problem is bonding, can I just do the old dodge of plugging in with a 3-to-2 connector? It seems to me that this would solve the GFCI problem, because any "ground-faulted" current ends up in the neutral limb anyway. But I'm not sure how bad the consequence of an overall-ungrounded trailer would be. Anybody know?

Thanks!

(Actually, I found this problem out when camping at a state park with GFCI-protected breakers on the 30 A connectors. How rude is that??)
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Old 09-14-2013, 10:12 AM   #2
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It's often a bad idea to plug a trailer with GFCI circuits into a GFCI shore power pedestal. The "upstream" (pedestal) GFCI can mistakenly recognize the internal circuitry of the trailer's GFCI as a fault.

BTW: Two GFCIs in series offers no more protection than does one GFCI all by itself.

Two work-arounds:
1 - Don't plug into a GFCI-protected pedestal; or
2 - Plug into the GFCI pedestal, but switch off the GFCI breaker in your trailer and don't use that circuit.
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Old 09-14-2013, 10:16 AM   #3
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If you remove the ground path from the supply chord it is dangerous.

If you really have a short to ground, this means a current carrying wire is touching either a ground wire or some portion of the metal body. When you remove the ground from the supply chord there is no where for a short current to flow, until a person standing on the outside of the trailer touches a metal portion of the trailer. Then that person becomes the ground, the current will flow through that person.

That is precisely what a ground fault breaker is designed to prevent.

To check for a bonded ground: Unplug first, then look inside the breaker box to see if there are two bars that look like the image below. All neutral, white, wires should connect to one. All ground, bare copper and green, wires should connect to the other. If any are on the wrong bar that is the trouble. The bar where all the white wires connect might have a screw that bonds it to the metal breaker box. That is a bonding screw. If this screw has not been removed that could be the problem. If there is only one bar, instead of two, where grounds and neutrals are connected, that is the problem.

Get help if you do not understand this!!!!
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Old 09-14-2013, 10:18 AM   #4
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Sad to choose one circuit or the other.

There is "one" way to work around....if you are capable and assume all risk.

Get a breaker of same type minus the GFCI feature, just a standard breaker.

When in park with that feature on pedestal, swap the breaker to non-GFCI.

I suppose it is "good news" thAt the campground is safer?????
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Old 09-14-2013, 11:49 AM   #5
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One way of quickly determining whether or not the ground and neutral are bonded together is to unplug the trailer, flip off the breakers and then check for continunity (a connection) between ground and neutral with a DVM. There should be no connection.

If you have only one bus bar in the box for both neutral and ground, you or an electrician can add another.

Note that only main entrance panels that have a real connection to ground should connect neutral and ground.

In a campground, the neutral line will _not_ be exactly at ground potential, particularly when there is heavy current draw due to ACs, etc; there will be a voltage drop in the neutral line just as there is in the hot line, so it is not uncommon to see the neutral a few volts above ground.

Of course, if your Airstream connects ground and neutral together, several amps of current will flow as the ground connection takes part of the AC load - and the gfci outside will immediately trip.

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Old 09-14-2013, 12:06 PM   #6
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BTW, it is fairly unusual for a 30 amp park outlet to be GFI protected. It is not a code requirement on the 30 amp ones, but is a code requirement on the 15 and 20 amp outlets. I have only seen a few 30 amp ones GFI protected.

That said, if more 30 amp outlets were GFI protected, you would hear/see/experience a whole lot more RV's with this issue of GFI tripping.

I actually feel that GFI protected 30 amp RV park outlets would be an excellent safety addition, but sure would cause a lot of hair pulling among park owners and RV owners.
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Old 09-14-2013, 12:35 PM   #7
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Originally Posted by idroba View Post
I actually feel that GFI protected 30 amp RV park outlets would be an excellent safety addition, but sure would cause a lot of hair pulling among park owners and RV owners.
While at Burning Man this year, our neighbor's converted bus was tripping the 20A GFI on the spider boxes (power distrib. boxes) we were using.. turned out to be the usual bonded neutral/ground problem.

Carrying a full set of adaptors, and debugging these sorts of problems at home is definitely the way to go for more relaxed traveling .

With all LED lighting, our trailer works quite nicely w/ just a 20A circuit, even with the AC running.

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Old 09-14-2013, 09:06 PM   #8
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Quote:
Originally Posted by A W Warn View Post
To check for a bonded ground: Unplug first, then look inside the breaker box to see if there are two bars that look like the image below. [snip]
Get help if you do not understand this!!!!
The thing is, the pedestal GFCI will trip even if all of the trailer's branch circuits are flipped to "off". So there can't possibly be a path from the output of the inverter/charger through to neutral and/or ground.

But of course the inverter/charger is a load itself. And I don't really understand the innards of the inverter / charger. Because this device sits between the pedestal's GFCI and the breaker box, it is obviously still in the circuit even if all of the trailer's breakers are switched off. So, the question is: can the pedestal GFCI still get tripped by a bonded breaker box with an inverter in the middle, even with all of the branch circuits switched off? Or not?

If not, I would need to look for the fault elsewhere.
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Old 09-14-2013, 09:16 PM   #9
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Quote:
Originally Posted by A W Warn View Post
If you remove the ground path from the supply chord it is dangerous.

If you really have a short to ground, this means a current carrying wire is touching either a ground wire or some portion of the metal body. When you remove the ground from the supply chord there is no where for a short current to flow, until a person standing on the outside of the trailer touches a metal portion of the trailer. Then that person becomes the ground, the current will flow through that person.

That is precisely what a ground fault breaker is designed to prevent.
But in a bonded trailer, the skin and all the other bits are in continuity with the neutral pin of the supply cable. So there *is* somewhere for the current to go: out the neutral.

I'm certainly not arguing that GFCI's don't make things safer. Of course they do. But a bonded trailer can't be protected by a GFCI'd supply line. The real question that I'm asking is *if* a trailer has a bonded ground, is it made any less safe by removing the ground pin from the supply line? And if so, why?

Seems to me that it might be less safe if the neutral weren't actually at 0 V, but I don't know if this is ever true, or not.
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Old 09-14-2013, 09:19 PM   #10
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The converter should not be "between" the supply and the trailer's breaker box.

It is simply an 120 volt AC appliance that makes 12 volts DC.

It should be connected to a breaker, in fact.



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Old 09-14-2013, 10:02 PM   #11
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Originally Posted by tlsmit1 View Post
The thing is, the pedestal GFCI will trip even if all of the trailer's branch circuits are flipped to "off". So there can't possibly be a path from the output of the inverter/charger through to neutral and/or ground.

But of course the inverter/charger is a load itself. And I don't really understand the innards of the inverter / charger. Because this device sits between the pedestal's GFCI and the breaker box, it is obviously still in the circuit even if all of the trailer's breakers are switched off. So, the question is: can the pedestal GFCI still get tripped by a bonded breaker box with an inverter in the middle, even with all of the branch circuits switched off? Or not?

If not, I would need to look for the fault elsewhere.
I can say that GFCI's are very sensitive devices and seem at times to have a mind of their own. It helps to understand how they work. I will try to be brief here. The GFCI measures the amp level going out on the hot line, and compares it with the amp level coming back through the neutral line. If they are not the same, within 0.005 amps (5 mA) it shuts the circuit down. The assumption is that the "missing" 5 mA is going through a person to ground. Since there have been recorded cases of death at 15 mA, the number they are set at has to be very low.

Now, that 5 mA could be leaking out through the insulation of the power cord to the trailer and going to ground. It also could be leaking 3 mA through a damp spider web inside the park outlet, and then only 2 more mA somewhere else will trip it out. A bad power cord could also leak internally the 5 mA between the hot and ground. There is also a real possibility that the park GFCI itself is defective and is too sensitive.

In addition, if the neutral and the ground line are bonded together somewhere in the system, part of the current going out the hot line on the GFIC will return on the ground line, not the neutral, and the GFIC will trip out. Again, only tiny amounts of leakage will cause this issue.

I have seen a GFIC trip when there was a leakage in the hot water element on an electric water heater. Most of the current came back through the neutral, but a little leaked to ground via the sheath and water in the heater. Pop goes the GFIC.

And so on...

My suggestion: First, does your trailer pop other GFIC's than the one on the 30 amp circuit in the park? If so, sounds like your trailer has the problem. If it trips the GFCI out with all the breakers in the trailer off, I would disconnect the power cord where it comes into the trailer and is still the rubber cord (first change from rubber cord to something else). If plugging it in (tape the ends of the hot and neutral wire) trips the GFIC, you have a defective cord and plug. If not, the problem is farther into the trailer, including bonding of the neutral and ground lines somewhere.

So, my brief answer became longer... the GFIC description was fairly brief....LOL.
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Old 09-14-2013, 10:15 PM   #12
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My 68 was tripping the GFCI. After several tries at finding the cause my Airstream buddy TomW suggested checking the condition of my outside 120 outlet. Sure enough, when I removed the cover the inside was wet and the back of the outlet was very corroded. I replaced the outlet and cover and it solved the problem. I should have thought about it because the problem started after a big rain..
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Old 09-14-2013, 10:24 PM   #13
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My suggestion: First, does your trailer pop other GFIC's than the one on the 30 amp circuit in the park? If so, sounds like your trailer has the problem. If it trips the GFCI out with all the breakers in the trailer off, I would disconnect the power cord where it comes into the trailer and is still the rubber cord (first change from rubber cord to something else). If plugging it in (tape the ends of the hot and neutral wire) trips the GFIC, you have a defective cord and plug. If not, the problem is farther into the trailer, including bonding of the neutral and ground lines somewhere.
Done those. Yes, the problem is in the trailer, because it'll pop a regular 20A residential GFCI if I plug the trailer into it. And the problem isn't the power cord because plugging the cord (alone) into the circuit doesn't pop the GFCI.

(Incidentally, I read the bit about taping the end of the cord. Yoiks, is the trailer-end of your supply cord MALE? Mine is female. Seems a much better idea!)

I'm still not sure, though, if bonding within the circuit panel that is supplied by the inverter--with all the circuits off--would pop the GFCI or not.
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Old 09-14-2013, 10:28 PM   #14
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Quote:
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The converter should not be "between" the supply and the trailer's breaker box. It is simply an 120 volt AC appliance that makes 12 volts DC.
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