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Old 08-09-2011, 06:44 PM   #1
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30A to 20A to bypass GFI?

My trailer has a 20A shore power umbilical. When I plug it into an extension cord running from my house, the 120VAC system in the trailer works. When I go to campgrounds (two separate ones so far) and try to plug into the 20A GFI outlets, I trip the breakers immediately.

I've been told the 50s era trailers might not use ground wires in the AC system, and since the GFI outlet is searching for a ground, it will trip if it doesn't find one. A technician suggested a bypass for this might be to use a 30A to 20A adapter since the 30A hookups don't use GFI. Is there a daring soul out there who tried this and lived?

Safety blah blah blah. I want lights!

I'm kidding. But could this be a viable work-around?
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Old 08-09-2011, 06:47 PM   #2
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If it trips the GFI there's a connection somewhere between neutral and ground, either deliberate or accidental. It's a hassle to do but the best and safest thing is to find and remove this connection.
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Old 08-09-2011, 06:51 PM   #3
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Agreed... but could this be the fifth best thing to do?
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Old 08-09-2011, 06:57 PM   #4
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Originally Posted by SpaceEgg View Post
Agreed... but could this be the fifth best thing to do?

Who knows, but playing with 30A of power in a all metal trailer with an ungrounded electrical system may be 1st worst thing you did......
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Old 08-09-2011, 07:29 PM   #5
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do you have a modern converter? i have read that some of these like to trip gfci's. before you tear the space ship apart, you might try unplugging the converter and see what happens.
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Old 08-09-2011, 07:36 PM   #6
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Most campgrounds have 20 amp outlets, this would be the easy fix. I like GFI.
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Old 08-10-2011, 11:10 AM   #7
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A tripping Ground Fault Interrupter is not guaranteed evidence of a kill-you-dead problem.

In a simple 120VAC circuit, power flows along two wires. They are called “line” and “neutral”. In modern romex wire, these are supposed to be the black and white wires, respectively. The bare copper is a ground. It is connected a ground rod at or near the electric meter. It serves to provide a path for the line side to flow to should the neutral fail, in an attempt to allow this current to find a return path and open a breaker or fuse somewhere.

A GFI device measures current as it flows through. If the GFI “sees” more current flowing on the line side than is returning on the neutral side, even as low as 3 or 4 milliamps, it “assumes” this extra current has found some path to ground and interrupts the flow. All this occurs in small fractions of a second.

The theory is this alternative path (ground fault) could be a human in some form of peril, and said human is getting the bejesus shocked out of themselves.

That all being said, the problem with the theory of simply measuring current is that in devices with copper windings, like electric motors, transformers and fluorescent lighting, current can “leak” to ground while the device is working normally and safely. Due to the sensitivity of the GFI, small leakage causes the device to trip.

I realize I went from Arkansas to California via Ohio to say that not plugging a trailer with an Air Conditioner and an AC to DC converter into a non-GFI outlet will save you all manner of grief, and not really expose you to any more chances of death than using a GFI, but at least you now know why.
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Old 08-10-2011, 11:29 AM   #8
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If any of your original two prong outlets have been replaced with three prong outlets you need to check that some bozo electrician did not tie the ground screw to the neutral screw with a jumper. I seem to see this all the time.
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Old 08-10-2011, 11:33 AM   #9
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adapters

okay, just as there are adapters to go from 30 amp male to 20 amp male, there are adapters to go from 30 amp female to 20 amp female. nothing nefarious about that. just go to camping world or other RV supply and get an adapter-problem solved. It is my understanding that a 59 A/S in stock wiring condition, does not have any grounding conductors. So, GFIC should not be used with them. Long term fix is to rewire the entire trailer. LOOOOOOONG term fix.
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Old 08-10-2011, 11:46 AM   #10
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a re-read was in order

I just reread this thread, and Mike L I am not sure I understand your post-any typo's in there? Going to the 59 trailer. 1st I have had NO direct experience with such an old trailer. But, as stated, I understand them not to have a grounding conductor within its 120VAC system. Now what Jeff posted is saying (I think I am reading his post correctly) is the GFCI of the park is reading a differential in current in the line and neutral-meaning some current is being bled off somewhere before it gets back to the pedestal. So, the chassis of the trailer must be a conductor allowing some current to get to earth ground, somehow-probably thru the tongue post. The converter is a good place for the AC neutral to be connected to the DC return (usually referred to as "ground" and as such the chassis of the trailer). That'd do it, I think-there must be a zillion old trlrs out there-how come nobody of the old, excuse me vintage iron-oops-aluminum-is answering this tread? Darkspeed being an obvious exception-with a darn good explanation, too.
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Old 08-10-2011, 12:05 PM   #11
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GFCI breakers tend to become super sensitive if they are flipped on and off a lot. Campground breakers are flipped on and off a lot and may be too sensitive and pick up a very small short in your system. Or it could be the converter as Ricky posted. Or a previous owner could have wired something backwards. Or Jeff's explanation about leakage to ground may be the answer.

You didn't say if you plugged the trailer into a GFCI circuit at home. That would be a better test since you would be comparing apples to apples.

If you have a small short in the trailer, you should track it down. It is fairly likely to get worse. Wire insulation in a 50+ year old trailer will have problems after many miles of rubbing the insulation on things.

But plugging into the 30 amp CG pedestal has other issues besides GFCI ones. If you have an electrical problem between the pedestal and the next breaker in the trailer, you will not have the protection of the proper sized breaker. However, people do the same type thing all the time when at a 50 amp pedestal without a 30 amp receptacle and they use an adapter (a "dogbone").

Given that plugging in at home has not caused the trailer to become akin to the electric chair may mean you have a very small short or some other issue that is not presently dangerous. To check the converter, you will have to do a work around by disconnecting it and connecting the 120 v. wires that go to it directly to the trailer breaker panel (do 1959 trailers have breakers or fuses?). But you will need to be plugged into a GFCI receptacle or circuit at home first to see if it trips when you plug in the trailer. If you haven't some experience with electrical work, this may not be for you.

To check for a short—others can explain it better than me. Finding out what is wrong will require checking for each of the suggestions you have gotten until by process of elimination you have found it. Do the thing that is simpler first and work toward the harder things.

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Old 08-10-2011, 12:08 PM   #12
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Another place to look is in the breaker/fuse box. It is common practice in some areas of the country to tie the ground (bare copper) and common (white) wires to the same buss bar in the fuse box. That was the problem in my Avion. I just separated the common (white) wires from the ground (Bare copper) wires and attached the white wires to their own buss bar that was insulated from ground. Now my trailer doesn't trip the GFI's at campgrounds.
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Old 08-10-2011, 12:59 PM   #13
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Quote:
Originally Posted by Darkspeed
Ground is tied to neutral at one location and that is at your service entrance. It is usually done with a green bonding screw that bonds the neutral buss to the case of the service panel. The service panel is grounded to earth through a ground rod.

If you have a separate sub panel with it's own ground rod then neutral will be bonded there as well

Your trailer outlet should have a hot / neutral / ground wire. This means your case ground is handled by your houses ( or whatever ) ground rod so there should be no connection between neutral and ground in your trailer.

I have inspected many structures that were neutral bonded in the wrong locations, it is done all the time.

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Old 08-10-2011, 01:23 PM   #14
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It is true common (white wire, also called neutral) and ground (bare or green wire) are often tied to the same buss in the household breaker box and then may go both to the ground rod (ground) and to the common from the street. Common is often called "ground" to further confuse everyone. I believe every breaker box I have seen in Colorado has been wired that way and it seems the way the buss bars are installed, there is no alternative. If this is done so "commonly", perhaps the NEC does not prohibit it.

The trailer does not have a ground rod and I doubt anyone will install one every time they camp. So, you are reliant on the campground ground wire. We use a tester every time we plug into shore power and so far, they've all been good.

Since I'm going to be working on installing a SurgeGard soon (today maybe, though I've been putting it off) and will see how the trailer was wired. Since I installed a new converter several weeks ago, I can't recall if the common and ground were tied together, but I will check to make sure they aren't.

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