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Old 08-07-2009, 09:11 PM   #1
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120 Volt short to shell - More ideas please

Hi,

I started a thread two days ago about a possible short that I presumed to be caused a wire on the outside light....I have since learned more about the problem - it is not caused by the outside light (12v shorts to give 50 volt vs ground!) but still need your help to track the source of the short.
See thread "Outside light as a source of shocks? " for background info.

In short "no pun intended", using a multimeter, I am seeing varying voltages vs ground...depending on how many of my breakers in the AS that I have flipped on. With all 3 of my breakers on (two 20Amp breakers and one 30Amp breaker) I will read 51 Volts from the aluminum skin to the somewhat wet ground. As I turn breakers off one at a time I will see lower and lower Voltage to ground...however even with all breakers off..tonight I had 4 to 5 volts measured from aluminum skin to ground. This voltage went to zero as I unplugged from the house. If I measure voltage to ground for each individual circuit (ie: as long as I am hooked to AC I measure Voltage from skin to ground) does this mean each circuit has a short - or does it possibly give a clue to the source of the short?

Not fully understanding how the univolt works, I then set to trying to isolate which circuit might be responsible. I sequentially remove each of the +ve leads from the univolt and then measured V vs Ground. I always measured ~50 volts. Oddly I can only read 0.2uA (micro amp) at 50volts.

What is my next step? I can't risk taking this out and hooking to AC - I was lucky last time when my daughter only felt a tingle.
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Old 08-07-2009, 10:22 PM   #2
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You have somewhat found what you are looking for already. The circuit with the worst leak should be checked first. The wiring in the small Airstreams is really very simple. You will need to further isolate where in the circuit it is leaking at. If you have a wiring diagram for your trailer it will be easier but you can do without.
First identify all of the things on the circuit in question. Unplug anything thats plugged into an outlet on that circuit and check the ground again. I had a bad cord on my refer, and I didn't even know it had a cord until I found it by accident. Nothing different? Then disconnect the power to the trailer and open the wiring connections and visually inspect them. Make sure that all of the outlets, lights, appliances etc. are wired correctly and that there are no loose wires anywhere. Anything that isn't working correctly is the first suspect. The wire you hooked up in the outside light may be contributing to the problem if its on 110volts. I wasn't clear if its 12v or 110v. If you don't find a loose connection somewhere I'll be suprised, but if you don't, the next thing I would check is the runs of wire in the walls. I disconnected both ends of the wire that ran from my breaker to my refer, and checked them for continuity to ground(the shell). If you find continuity it means a bare wire in the wall is grounding to the shell. Almost impossible to repair without major surgery. I was lucky in that my problem was just in the refer cord grounding to the frame of the refer because it was cracked and frayed. You may need to do this to isolate the problem if its not in a junction box or outlet/ light fixture where you can get to it.

I hope this helps. I'm not a professional electrician. I just pay attention to what they have to say so I don't kill myself with my own little projects.

Best of luck to you.
Rich
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Old 08-07-2009, 10:52 PM   #3
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Mine was an easy fix.....worth checking

I got shocked, twice ( Once at a campground, once at a rodeo grounds ). The polarity of the outlet was switched at the campground. The polarity of the extension cord was switched ( a "repaired" cord ) at the rodeo. My Argosy has a light to warn of this problem. I was afraid to test it though. It works. I now have a plug in outlet tester that is always plugged in.
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Old 08-07-2009, 11:52 PM   #4
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Hi, the easiest and most common cause of this situation is, you are plugged into an ungrounded [or two wire] recepticle. Check this first before taking your trailer apart piece by piece.
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Old 08-08-2009, 04:38 AM   #5
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don't forget to inspect the ends of the power cord for cracks. also, if the end has been replaced, check the wiring inside.
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Old 08-08-2009, 09:16 AM   #6
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Smile Short found and repaired - Thanks very much



Well, talk about getting overly complicated.
It was too simple.
Checked the outside GFI - all ok.
Checked the extension cord - all ok.
Next in the circuit was the adapter between the home extension cord and the trailer power cord. Voila!

The ground pin connector in the adapter was not able to make contact with the ground pin on the extension cord due to a small piece of plastic that had broken off internally. Once I repaired this the voltage to ground from the skin of the trailer was <1 +/- .5 vollts. SHould it be absolute zero volts????

I then checked my receptacle that had previously shown open ground and it too now read okay.

One nagging question though, the incident that started this whole investigation was that my daughter had complained of tingling in her hand when ever she touched the door handle (bare feet, wet ground). This occured at a provincial park that did not require me to use the broken power cord adapter.

I'll have to monitor the volts to ground and use the plug in ground check light as a precaution going forward....a good idea regardless of the park.

So, does anyone know where you can buy those single plugin outside receptacles. While investigating this whole thing mine broke upon removal from the trailer. It has a nice chrome faceplate that I'd like to keep.


Thanks again all for the great advice. In 3 days I've learned more about Univots, DC and AC wiring and grounds vs neutral than I had in the 3 years I've owned the trailer.

Julsion
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Old 08-08-2009, 10:18 AM   #7
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glad to here you found your problem Julison. I still think that the campground you were plugged in at had a problem and not your trailer.
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Old 08-08-2009, 03:56 PM   #8
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There's a chance it could have been the campgrounds power that was the problem.
When I first got my safari home I took off all of the coverplates and light covers and inspected all of the connections. I am very impressed with the quality of the workmanship that went into the wiring on my trailer. It was better than any house wiring job that I've seen. Still, being 45 years old it was needing to be looked at. I found several problems inside switches and outlets, and some of the rotary light switches were intermittent. My battery wires were almost gone at one connection and the fuse block had broken loose from its mount.
I learned alot about the electrical system and how it was installed and after fixing the things I found that were messed up I'm very confident in the electrical system lasting a very long time. One of the things I'm doing to improve the system is to replace the converter(mine was not called a Univolt) with a Progressive Dynamics power control center. I suggest these to everyone who has the old converters or Univolts because they have a built-in 4 stage charge wizard to take great care of your batteries, and they are also a converter, a 12v fuse box, and a 110v breaker box. They have them at Vintage Trailer Supply for a very reasonable amount. Mine will be installed very soon and I'll post the results on my blog.
Glad you found the(a) problem and no one was seriously injured.
Rich
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Old 08-08-2009, 07:38 PM   #9
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Quote:
Originally Posted by Julison View Post

One nagging question though, the incident that started this whole investigation was that my daughter had complained of tingling in her hand when ever she touched the door handle (bare feet, wet ground). This occured at a provincial park that did not require me to use the broken power cord adapter.
Julsion
That sounds like a polarity problem, most likely the campgrounds wiring.
To be safe, I reccomend a plug in polarity checker. One red light, two green. different lights combinations ( on or off ) tell you what the problem is, or if you have a problem. I hook mine up to an interior outlet in the camper,..... the end of the line. If that outlet shows good, everything leading to it is good. My daughter got a shock the same way, bare feet, wet ground.
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Old 08-16-2009, 06:44 PM   #10
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Still some weirdness at play here

OK,

I've been thinking about my poor ground situation that I had due to the broken 20 to 30A plugin adapter. Before I got the new adapter I had 51 volts from shell to ground. After the new adapter < 1 volt (atlhough this evening I registered 1.9 volts). My question is, why should there be any volts to ground if with or without proper grounding wire? Shouldn't I read near 0 volts regardless of ground or not? I thought the grounding wire was just a protection incase there is a hot short somewhere.

So I went back to the trailer to explore the voltage leak. I started by shutting off all breakers and checking Voltage to ground. I was expecting zero volts (the same as I get when I don't have the trailer plugged in at all) but I still had the 1.9 volts shell to ground! I checked all 120 outlets to ensure the breaker were working and there was no power at the outlets. For sanity check I then unplugged the trailer and the voltage on the multimeter went to zero.

Would this suggest that the hot short is somewhere BEFORE the breaker box? It doesn't leave many places to check....just the line in I think.
Does the line to the univolt first go through the breaker box?

thanks all for any help with this,

Julison
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