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#17142 - 11/21/02 10:14 AM Bad Trailer Bond and Ground Fault
sparky66wv Offline
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Registered: 11/17/00
Posts: 2232
Loc: West Virginia
This new thread expands on this one:

Rescue Work Near Miss

After disconnecting the faulty circuit the other day, and re-doing the bond yesterday, I went ahead and installed AFCIs today, which took some work because I had used a multiwire to feed the two circuits in a junction box. So I added a cable to the junction, split up the neutrals and hots and nutted off the red wire in the 12-3-G.

First I measured again for resistance to ground from hot to ground on the faulty circuit. 14 Ohms. Wow, that translates to roughly 8.5 Amps, not enough to open a normal OCPD.

I connnect the normal Breaker in and turn it on. No tripping, no noise, nothing. Measure amperage, Hmmmph. Nothing!

Replace with the AFCI and it holds. Then I turn on a light and it trips. OK, the second part was expected but I'm still confused.

Measurements of the fault were 114V from door threshold to cover screw on panel. This was before the bond repair, which dropped it to 0V.

I really expected to see some current (say 8.5A) when the circuit was energized and I expected subsequently, that the AFCI would trip instantly do to the ground fault.

What in the world is going on here, and does it help me in any way to locate the fault?

I gotta start tearing out walls and siding the next clear, sunny day.



Anyway, so far, this application makes me glad that AFCIs are available, I just wish they'd do more...
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#17143 - 11/21/02 11:02 AM Re: Bad Trailer Bond and Ground Fault
txsparky Offline
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Registered: 05/25/01
Posts: 552
Loc: Magnolia,.Texas U.S.A.
If it trips when you turn on the light,the fault is in the switchleg or fixture.(Why did you expect it to trip?)

[This message has been edited by txsparky (edited 11-21-2002).]
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#17144 - 11/21/02 01:00 PM Re: Bad Trailer Bond and Ground Fault
sparky66wv Offline
Member
Registered: 11/17/00
Posts: 2232
Loc: West Virginia
Not that simple...

The fault might very well be in a switch leg, I can't disprove that, but before the trailer was bonded and before the AFCI installed, the lights worked fine (went off and on like normal) but there was voltage on the trailer (114V), with or without the lights being on.

The AFCI tripping is normal for a ground to neutral short, I guess I meant to say, that once it didn't trip initially, then I fully expected to trip under load, which it did.

We tried two lights and the same thing happened in both places, now the chances of two switch legs being faulted on the same circuit would be kinda slim, but possible.

I'll try to add another load and I fully expect it to trip then, which would indicate a neutral to ground fault.

Sorry if I haven't been descriptive enough.

I guess the puzzle is:

How can I have 14 Ohms, 114V and have 0 amps?

How can I have both a neutral to ground fault and a hot to ground fault (presumeably on the same cable) without tripping the OCPD or atleast drawing some measurable current?

Is "Argile's Law" coming into play here?



[This message has been edited by sparky66wv (edited 11-21-2002).]
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#17145 - 11/21/02 01:30 PM Re: Bad Trailer Bond and Ground Fault
txsparky Offline
Member
Registered: 05/25/01
Posts: 552
Loc: Magnolia,.Texas U.S.A.
Quote:
Is "Argile's Law" coming into play here?


God I hope not!
Have to ask.....
Are you absolutely positive that nothing was plugged into this circuit and that all switches were off when you ohmed it?

I remember a thread where an AM radio was used to find a fault.Did you read that one?Might be worth a try rather than removing siding and tearing out walls.(unless you need to take out some frustrations )

[This message has been edited by txsparky (edited 11-21-2002).]
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#17146 - 11/21/02 01:43 PM Re: Bad Trailer Bond and Ground Fault
Tom Offline
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Registered: 01/01/01
Posts: 1044
Loc: Shinnston, WV USA
Virgil,

I think you are ohming an inductive load such as a transformer (for a doorbell or battery charger, etc), The reason I suggest an inducitve load is that the ohm reading has little to do with how much current the load will draw. If the load is a small one, you may not be able to measure it with a clamp on. As far as I know, you could even be reading a GFI receptacle.

I believe arc fault devices contain a 30 ma GFI. If there is the slightest neutral to ground connection or pathway downstream, the arc fault breaker will trip.

Take the following ohm measurement- disconnect the neutral of the circuit at the panel & see if you get a reading to ground. You should be reading millions of ohms, a lower reading could be low enough to trip the GFI portion of the breaker.

Dad blast these tornado magnets anyhow.

Tom
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#17147 - 11/21/02 02:06 PM Re: Bad Trailer Bond and Ground Fault
Tom Offline
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Registered: 01/01/01
Posts: 1044
Loc: Shinnston, WV USA
Well, I went & clicked on the link you provided. Now my curiosity is really up.

What was on the circuit that initially energized the frame of the mobile home?

I've had a similar problem in the past & what you may be looking for a high impedance ground fault in an appliance. This fault would impress line voltage on the frame, but the resistance of the fault itself may be so high as to limit current flow to such a low value that it is difficult to measure. Also, the fault could be on a busted or damaged neutral in the appliance.

Whatever the problem was that put the voltage on the frame probably still exists.

You might try making your own current transformer for your clamp on & putting it around the new bond wire you installed. I'd bet that it is carrying a small current in the Ma range. Try you lowest scale on the clamp on, with one piece of insulated wire, wrap 10 turns of wire around one jaw, wrap one turn around the bond wire you installed, then connect the two ends together with a wirenut. Divide any reading you get by 10.

Looking forward to the next thrilling adventure in the continuing saga of "minimum standard wiring."
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#17148 - 11/21/02 02:31 PM Re: Bad Trailer Bond and Ground Fault
txsparky Offline
Member
Registered: 05/25/01
Posts: 552
Loc: Magnolia,.Texas U.S.A.
I had a mobile home that the owner had put chicken wire around it to keep the dogs from getting under it.The complaint was that frogs kept getting electrocuted by the wire.It was acting like a bug zapper.Turned out to be a 30 amp dryer receptacle wired wrong.
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#17149 - 11/21/02 03:00 PM Re: Bad Trailer Bond and Ground Fault
sparky Offline
Member
Registered: 10/18/00
Posts: 5303
Quote:
Try you lowest scale on the clamp on, with one piece of insulated wire, wrap 10 turns of wire around one jaw, wrap one turn around the bond wire you installed, then connect the two ends together with a wirenut. Divide any reading you get by 10.


quite inovative Tom.

Do you suppose that one could remove one nuetral at a time ( assuming no multiwires) and assess per said method?
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#17150 - 11/21/02 03:44 PM Re: Bad Trailer Bond and Ground Fault
Tom Offline
Member
Registered: 01/01/01
Posts: 1044
Loc: Shinnston, WV USA
Sparky,

Not too sure about lifting one neutral at a time. It would be interesting to see what happens if that was done.

I'm also wondering if Virgil is dealing with more than one problem on this job. When you're working with a junky wiring system, fixing one problem frequently exposes another one
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#17151 - 11/21/02 07:51 PM Re: Bad Trailer Bond and Ground Fault
sparky66wv Offline
Member
Registered: 11/17/00
Posts: 2232
Loc: West Virginia
Thanks for all the input, guys.

Donnie, I may have to try the AM radio idea. Unless the thing buzzes consistantly within 4' of the trailer... I guess the buzz would get louder the closer I get to the source?

I'm fairly sure all loads are unplugged, unless it's less than a 0.1A load... Could be a wall-wart... But I think only lighting is on this circuit. It's the only 14 guage cable, and the other two seem to operate the various receptacles. One circuit isn't attached at all. Neither are the two new ones (roughed in for the addition, not by me), except neutral and grounds.

Yeah Tom... Really old trailer... I'd say late 40's. No GFCIs, Everything is apparently plugged into one surge protector with zip-type extension cords everywhere...

Sigh...

I'm going to get pictures the next time I'm there, either tomorrow or Saturday. The whole thing is unbelievable.

Steve, I'll try the neutral lifting idea too, and see what happens. That would indicate a fault under load, wouldn't it?

No wait a sec... I'm wrong. The #14 isn't the faulty circuit. It's one of the two #12's I had on the multiwire originally. I guess the lights are on #12? I better double check and keep the extra 15A AFCI I got just in case....

Tom's right... It a nightmare...

Dern Tornado Magnets is right!

[This message has been edited by sparky66wv (edited 11-21-2002).]
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