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Old 01-14-2014, 05:00 PM   #1
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Default Locating short in underground conduit

Hello all: I have a 12/3 run of about 60' partly indoors and partly in a PVC conduit. Problem: there is a short from ground to neutral. Question: How to locate the short: Most of the equipment to locate cables and shorts is very costly. Any way to deduct the distance from the end to the short? Kind Regards, Jon

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Old 01-14-2014, 05:18 PM   #2
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Is there a gfi on that circuit

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Old 01-14-2014, 05:48 PM   #3
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Originally Posted by Jon Paul View Post
Hello all: I have a 12/3 run of about 60' partly indoors and partly in a PVC conduit. Problem: there is a short from ground to neutral. Question: How to locate the short: Most of the equipment to locate cables and shorts is very costly. Any way to deduct the distance from the end to the short? Kind Regards, Jon
If its that short of a run in pipe just replace the wire.
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Old 01-14-2014, 05:49 PM   #4
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what's the point of locating the fault ? pull it out and replace
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Old 01-14-2014, 06:07 PM   #5
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I agree with all of the above but to answer the mans question, a time domain refeclometer will tell you where it is.
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Old 01-14-2014, 06:13 PM   #6
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I've always wondered why anyone would spend thousands on test equipment when there's no need for it.
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Old 01-14-2014, 06:26 PM   #7
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Sounds like somebody put Romex underground. Did they use plumbing PVC fittings as well?
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Old 01-14-2014, 06:27 PM   #8
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Sounds like somebody put Romex underground. Did they use plumbing PVC fittings as well?
Yeah, forget UF......
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Old 01-14-2014, 06:31 PM   #9
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Right.... just replace the wire it probably much easier than renting equipement to locate the short, digging it up... then what... splicing .... that's not a good idea anyway.
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Old 01-14-2014, 06:35 PM   #10
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Connect some new wire to the old wire pull the old wire out and you won't have to locate a short in the wire. Scrap the old wire.
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Old 01-14-2014, 06:38 PM   #11
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I would also just pull THWN in the conduit because that is much easier than pulling UF into conduit.
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Old 01-14-2014, 10:27 PM   #12
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there is a short from ground to neutral.
get rid of the arc-fault breaker and call it a day. lol

I would use a locator that our company has...but I have no idea what those things cost to buy or rent...

I agree with what others have said, get rid of it and run a new romex to the box that the PVC is connected to, and from there pull 12 awg thwn.
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Old 01-15-2014, 06:18 AM   #13
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Hello all: The conduit is PVC 3/4" SCH 40 electrical, a total run of 75' in several sections. There is no GFI and I am testing directly at the wire ends disconnected from the connectors and system. It was installed poorly, with many sharp bends and a U turn. No junction boxes or pull elbows to access it. It will be very hard to easily pull a new wire. If I know the fault location even approximately, I can localize the area and save time. One solution may be a milliohm meter, measure the loop resistance at each of the ends and calculate the resistance, assuming the fault is a dead short. I am open to your further ideas! With Kind Regards, Jon
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Old 01-15-2014, 08:23 AM   #14
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One solution may be a milliohm meter, measure the loop resistance at each of the ends and calculate the resistance, assuming the fault is a dead short.
Good thinking, but the chances of a zero ohm short is pushing it. Actually though, it wouldn't have to be a perfect short, but a consistent short that you could add to your calculations on each end. Don't move the wires around too much while you are doing this.
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Old 01-15-2014, 09:17 AM   #15
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Rent one from another electrical firm or just have them locate it for you. The $100 it cost will be well worth it to your customer. I am guessing you already have waaay to many hours in this already.
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Old 01-15-2014, 09:53 AM   #16
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Hello all: Being an electrical engineer, I thought of 2 tests: #1 4 terminal resistance, #2 apply a powerful AC oscillator (audio or RF) and detect the field with an amplifier and headset like used to telephone lines. I found an old Fluke 8842A DVM in my pile of old equipment, it can read milliohms (4 terminal 4 lead measurement). I will check loop resistance from both near and far end and calculate, #12 ga has 1.588 Ohm/1000 ft. Just by comparing the near/far resistance I may get a clew, which section to replace and if the short is accessible in an elbow or junction. Cheers, Jon
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Old 01-15-2014, 10:40 AM   #17
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"Just by comparing the near/far resistance I may get a clew, which section to replace and if the short is accessible in an elbow or junction. "

But you just wrote that there are no pull elbows and no junctions.

Don't forget that there may be more than one short, or potential short, and fixing one damaged section may not be the end of it. Jobs that are done badly have a tendency to outwit all who try to apply logic. What if you locate the area, and find the insulation was stripped back for several feet? This is common in pulls with too many bends or where the conduit has sharp edges left in.

I think you'll best serve your customer by recommending a complete replacement of the conduit and wiring with a system that meets code.
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Old 01-15-2014, 12:12 PM   #18
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I think you'll best serve your customer by recommending a complete replacement of the conduit and wiring with a system that meets code.
Couldn't agree more. When I see an installation that is so bad I can't do a guaranteed a repair. I recommend replacement and give my price. Any splice to NM underground will not be code compliant and I would not be able to guarantee it so I would price replacing the whole thing.

Add a junction box in both buildings where the conduit exits the building. would allow you to replace the underground and splice it. But if even the inside install is really bad I would replace that too.

Any pictures of this install?

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Old 01-15-2014, 06:47 PM   #19
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Hello all: I have a 12/3 run of about 60' partly indoors and partly in a PVC conduit. Problem: there is a short from ground to neutral. Question: How to locate the short: Most of the equipment to locate cables and shorts is very costly. Any way to deduct the distance from the end to the short? Kind Regards, Jon
At that distance, pulling in three new wires would be quicker than posting on this forum.
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Old 01-15-2014, 07:34 PM   #20
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Start digging

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