Trouble shooting under ground feeder

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codeunderstanding

Senior Member
In trouble shooting a detached garage I came across the following voltages.
116v phase to phase
116v phase to ground
0v phase to ground

Nothing in the garage works now. Why would you have 116v ph to ph when one phase to ground is 116v and the other phase to ground is 0?
 
Dennis Alwon

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
It appears you have a bad hot wire going to the garage. What you are doing is reading the neutral thru one phase. I think
 
C

Cow

Senior Member
Location
Eastern Oregon
Occupation
Electrician
codeunderstanding said:
In trouble shooting a detached garage I came across the following voltages.
116v phase to phase
116v phase to ground
0v phase to ground

Nothing in the garage works now. Why would you have 116v ph to ph when one phase to ground is 116v and the other phase to ground is 0?
Click to expand...

Another possibility is you are reading 116v phase-phase because one phase has opened up under ground and is now grounded out.

Are you taking these readings at the garage panel with the main off?

Sounds like you need to get out the fault finder...
 
H

hoozonfirst

Member
I would assume one phase is going to ground, the other is good, and you have probably lost your neutral as well, hence the "good" phase not working.
 
C

codeunderstanding

Senior Member
480sparky said:
One leg is grounded then. Time to get a fault locator. :)
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What would be a good locator to get. i dont have one yet because I dont do to many of these under ground faults. I looked to rent one today but I couldnt find one to rent.

I would not want to go over $500.00 if one at that price would work well.
 
480sparky

480sparky

Senior Member
Location
Iowegia
codeunderstanding said:
What would be a good locator to get. i dont have one yet because I dont do to many of these under ground faults. I looked to rent one today but I couldnt find one to rent.

I would not want to go over $500.00 if one at that price would work well.
Click to expand...

They sell new for around $1200. I've seen used ones on fleabay for $500-600.

But the biggest secret is to charge for it. If you charge $150 for a 1-hour service call, then you need to charge $300 for a fault locate. NEVER charge your standard rates for getting out high-end test equipment.
 
Dennis Alwon

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
How long is the run? It may be cheaper to replace the entire run. This is why I run to my remote buildings with conduit.
 
J

Jay Dubz

Member
Why buy an expensive ground fault locator when it is obvious that one-leg of this circuit has completely grounded out, which mean a possible knick in the insulation or break in the wire. Continuity testing should give you your answer.

And if one ungrounded leg and the neutral both have shorted, then there is a strong possibility that the integrity of the underground feeder, be it UF cable or pipe has been totally compromised, i.e., ?severely damaged?. Just replace the circuit.

Also, I?m sure you?ve checked for any ?hidden? J-boxes or bad splicing on the line-side of this feeder within the house?
 
J

Jay Dubz

Member
Why buy an expensive ground fault locator when it is obvious that one-leg of this circuit has completely grounded out, which mean a possible knick in the insulation or break in the wire. Continuity testing should give you your answer.

And if one ungrounded leg and the neutral both have shorted, then there is a strong possibility that the integrity of the underground feeder, be it UF cable or pipe has been compromised, i.e., ?severely damaged?. Just replace the circuit. I?m sure you?ve checked for any ?hidden? J-boxes or bad splicing on the line-side of this feeder within the house?
 
ptonsparky

ptonsparky

Tom
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
Just replace the circuit isn't always the answer even if short. The 3wire that fed the garage for 30 years may now have to be a 4 wire. Add some rods, an EG bar for the FPE panel, isolate the neutrals. Dang, a range they last used for canning 10 years ago but want to keep. It just keeps adding.
 
J

Jay Dubz

Member
ptonsparky said:
Just replace the circuit isn't always the answer even if short. The 3wire that fed the garage for 30 years may now have to be a 4 wire. Add some rods, an EG bar for the FPE panel, isolate the neutrals. Dang, a range they last used for canning 10 years ago but want to keep. It just keeps adding.
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I agree, but if it was buried in pipe this would be the cheapest, quickest, and only reasonable approach if the raceway is still sound. And if it?s UF or USE type sheathing (without conduit) I still think that replacing a buried cable which has possibly somewhat degraded over time is better than repairing an underground splice, for overtime more problems may arise in another unseen buried location along this same cable run.

There are many unknown factors to consider as it pertains to why this circuit may be shorted, i.e., damaged underground. Was it improperly spliced beneath the grade? Was it buried too shallow and cut during some yard work? Is it in pipe or the proper type of underground feeder sheathed cable? I only recommend replacement before going out and buying such an expensive piece of equipment to troubleshoot a garage subfeed.
 
C

Cow

Senior Member
Location
Eastern Oregon
Occupation
Electrician
Jay Dubz said:
Why buy an expensive ground fault locator when it is obvious that one-leg of this circuit has completely grounded out, which mean a possible knick in the insulation or break in the wire. Continuity testing should give you your answer.

And if one ungrounded leg and the neutral both have shorted, then there is a strong possibility that the integrity of the underground feeder, be it UF cable or pipe has been compromised, i.e., “severely damaged”. Just replace the circuit. I’m sure you’ve checked for any “hidden” J-boxes or bad splicing on the line-side of this feeder within the house?
Click to expand...

Your answer makes it obvious you must not own a ground fault locator either. The original poster made no mention of how long the distance is, making a blanket statement of "just replace the circuit" doesn't make any sense without knowing the distance. It could be 400' long, why spend that kind of money, when you could probably find/repair it in under 2 hrs?

Secondly, it could be direct bury USE, rather than pvc/UF like you mentioned. Very easy to repair underground once the fault is found. And no, just because one wire is compromised doesn't mean the rest are. So it doesn't automatically call for the whole circuit to be replaced.
 
480sparky

480sparky

Senior Member
Location
Iowegia
Jay Dubz said:
Why buy an expensive ground fault locator when it is obvious that one-leg of this circuit has completely grounded out, which mean a possible knick in the insulation or break in the wire. Continuity testing should give you your answer. ......
Click to expand...


Show me how to locate a fault with a continuity tester. :cool:
 
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