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Old 03-26-2010, 04:36 PM   #1
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Potential Ground Fault issue? Diagnosis?


I built a free standing garage with main power tapped from the home breaker box. The contractor pulled 4 wires via a conduit to the freestanding garage panel which supplies lights, a garage door, and two 20 amp outlets.

Everything worked well initially, but about 1 week ago one section of the lights in the building went out. The contractor came out and found that one of the two hot wires in the garage panel was only seeing 100 volts and that went down if anything else was turned on. He swapped one of the ground wires for the bad hot wire and everything now works.

What would cause a situation like this where the hot wire apparently had a voltage loss? Is it safe to continue with the fix where the faulty wire is now the ground?

Thanks in advance!
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Old 03-26-2010, 05:18 PM   #2
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If the voltage on one leg goes up when the other leg goes down, it is a sign of a poor neutral connection. W ould have a new neutral installed if checking the connections does not fix the issue.
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Old 03-26-2010, 06:49 PM   #3
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So now you don't have a ground ?
No, that's not safe
In addition most grounds are smaller then the hots
Possible he ran all the same size



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Old 03-26-2010, 07:05 PM   #4
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thanks for the replies y'all!

what he did was switch one of the two hots for one of the two grounds. So now the old hot wire is the ground and the old ground is the hot.

Thing is..everything worked fine for a couple of weeks...

I believe he ran the same gauge for both the ground and hot...looked that way to me, but I'll double check.

My main concern is safety now that the old hot wire (the one that didn't work) is the ground....he said when it was hot it was running about 100 volts so there was some continuity there and that's why he felt comfortable using as a ground.

I'd like to know it's safe so I don't shock myself or burn anything up. Also curious as to what would cause this scenario to happen to start.

thanks again!

Tony
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Old 03-26-2010, 07:37 PM   #5
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You do not have 2 ground wires.
You have a ground and a neutral wire.
If the hot wire was not carrying the full voltage, it may have a bad connection, or could have a skint place on the insulation.
Either way, this wire needs to be replace and the problem fixed.
What size wire did he run?
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Old 03-26-2010, 08:13 PM   #6
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I think you have three problems.

1. The insulation on one of the wires got torn causing a short between that wire and the conduit.

2. There is a problem with the neutral resulting in 100 volts (which keeps changing) to some loads.

3. The wire colors are now wrong because wires got switched. (If they are #4 or fatter and not green, then you can put colored tape on the ends (both ends of each affeted wire).

I would go ahead and use the damaged wire as the ground, assuming that the other criteria such as mentioned above were met and assuming the copper itself was not cut. If the neutral was the damaged wire and was cut all the way through, then you could have the 100 volt problem.
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Last edited by AllanJ; 03-26-2010 at 08:22 PM.
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Old 03-26-2010, 08:33 PM   #7
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Quote:
Originally Posted by AllanJ View Post
I think you have three problems.

1. The insulation on one of the wires got torn causing a short between that wire and the conduit.
In a perfect world wouldn't this result in a tripped breaker?
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Old 03-26-2010, 08:42 PM   #8
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here is what I know:

The conduit is plastic and runs from the main house under a driveway and into the breaker panel. The contractor referred to there being two "legs" to the building panel. One leg was good, and the other had the 100 volt problem which was "fixed" by swapping the hot and ground.

The building has two separate ground rods placed outside...that's why I thought there were two grounds.

If the plastic conduit developed condensation inside and the insulation is torn, could this cause the problem?

I think the wire gauges are the same but I will check tomorrow. Not sure on the colors either, but will check that as well.

thanks again for the help,

Tony
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Old 03-26-2010, 08:44 PM   #9
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Quote:
Originally Posted by jlmran View Post
In a perfect world wouldn't this result in a tripped breaker?
In a perfect world there wouldn't be any problems



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Old 03-26-2010, 09:33 PM   #10
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In my opinion, if the original hot conductor can't carry the proper voltage correctly, then I would be cautious in using it as a bonding (grounding) conductor, as evidenced by your electrician's switch-a-roo. If it is physically damaged, and, if ever you needed it to clear a fault, the damage may prevent it from quickly clearing the fault. Certainly check all connections before implicating the conductor. Again, my opinion only.
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Old 03-26-2010, 10:10 PM   #11
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What do the two hots, neutral and ground feed as they enter the building? Where are they fed from? What size circuit breaker are the two hots being fed from.
But, I agree with the previous post, the old switcheroo is not a good practice. Most likely you have a damaged conductor which isn't good for hots, neutral or grounds. Measuring that wire with a meter, if not a megger, would be a good idea.
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Old 03-27-2010, 08:01 AM   #12
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Do loaded continuity tests using the wires two at a time, one hooked up to a 20 amp. breaker and the other to the neutral bus at the main panel (use pigtails if needed) for a few minutes for testing. Use a moderate load such as a hair dryer at the other end. Measure the voltage. This is to prove that no wire was nearly severed.

Also (problem you could have instead of one mentioned above) if one hot wire is disconnected or severed and there are 240 volt only loads (such as heaters) in use, the 120 volt loads on the bad side of the 120/240 volt subpanel line can see low voltage. Current would flow out the good hot wire, through the 240 volt load, over to the other side of the line at the subpanel which is isolated for the moment, through a 120 volt load, to neutral, and back to the main panel, the latter being a series circuit with two of your loads.
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Last edited by AllanJ; 03-27-2010 at 08:21 AM.
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Old 03-27-2010, 07:48 PM   #13
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If it was my job,I'd pull the conductors out and examine them for other damage.Better than coming back repeatedly,losing future work.
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