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Old 09-26-2009, 01:51 PM   #1
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Underground short on exterior lighting


Is there a reasonably easy way to find out where there is a short underground between post lights, without digging up the whole yard and wiring. The wire is buried about 2 1/2 to 3 feet underground. I know you can find a break in an underground invisable fence system for pets by using an am/fm radio but that is only a max of 6 inches. Please help before i loose my mind
Thanks

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Old 09-26-2009, 05:26 PM   #2
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Underground short on exterior lighting


Irish,Do you have a Short? or an Open? A Short means the C/B trips, an Open means no power. Either way the problem may not be easily solved. What does "between post lights" mean? 10 ft? 100 ft?. Thanks for including the depth which is much deeper than code requirements. How do you know it's that deep? Is it direct burial or in conduit.

Is the problem on a 120V circuit or is it low voltage (12V)?

If you can see a cable going into the ground, what color is it. Do you have Gophers?

Sorry for all the questions but these are all relevant because you didn't include much information with your question.
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Last edited by PaliBob; 09-26-2009 at 05:30 PM.
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Old 09-26-2009, 07:05 PM   #3
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Underground short on exterior lighting


Is this new or old existing wiring? If OLD then may just be a whole bunch easier to just run new wire to the lights.
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Old 09-26-2009, 09:09 PM   #4
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Underground short on exterior lighting


Its new wiring, about 2 years old
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Old 09-26-2009, 09:24 PM   #5
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Underground short on exterior lighting


Direct burial, or conduit?
Where are you located ?
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Old 09-26-2009, 09:33 PM   #6
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Underground short on exterior lighting


Hi Palibob
the light posts are about 150 feet apart, , the wire is approx. 2 feet deep (we dug the ditch ourselves because the electricians didn't want to do it) and we laid a gray cable directly into the ditch, had it inspected by the electrical inspector, filled it in and the rest the electrician did. (It's not in conduit), we just installed GFI's on each of the other two light posts just to find out which one was tripping the whole circuit and thats how we narrowed it down to the last light post. The wiring is about 2 years old and b4 now, everytime it rained thay would short out, but until recently we have been able to reset it and it would be fine for a while, now, it's just given up , propably fromthe wet summer we had. No we don't have gophers, just my husband .... digging up the yard looking for the solution. It's 120V Thanks for your help
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Old 09-26-2009, 09:34 PM   #7
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Underground short on exterior lighting


Direct Burial...NJ
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Old 09-26-2009, 09:45 PM   #8
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Underground short on exterior lighting


I guess if it's a wet insulation problem and it doesn't trip the CB [just the GFCI] you might be able to fix it by powering a hair dryer at the far end with the GFCI bypassed. The heavy current may dry out the wire.

Or, rent one of these
http://en.wikipedia.org/wiki/Time-domain_reflectometer

Last edited by Yoyizit; 09-26-2009 at 09:48 PM.
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Old 09-27-2009, 05:03 AM   #9
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Underground short on exterior lighting


Quote:
Originally Posted by frustratedhalf View Post
the light posts are about 150 feet apart,.........
we just installed GFI's on each of the other two light posts .........

b4 now, everytime it rained thay would short out, but until recently we have been able to reset it and it would be fine for a while,......

probably from the wet summer we had.
Frustrated, We're making progress. it appears that you have a GFI that trips due to a fault current leakage path that exceeds 5mA through all that buried cable

Now let me see if I understand the layout

1) Three Light Posts, each about 150' apart
2) There appears to be a problem between Post #2 and Post #3
3) Light Post #1 and #2 have a new GFI to isolate the problem

Question, Is there an original GFI
that fed all three Posts and where is it located?

If there is a buried cable to Post #1 ?
How long is it?
How long is the total length of buried cable?
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Last edited by PaliBob; 09-27-2009 at 05:12 AM. Reason: sp
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Old 09-27-2009, 10:28 AM   #10
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Underground short on exterior lighting


"Normal" leakage current for 150' of Romex @ 60Hz is 0.8 mA with 450' using up half of your 5 mA "leakage budget".

With fixture capacitance your design might be marginal from the get-go.
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Old 09-27-2009, 10:58 AM   #11
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Underground short on exterior lighting


Replace it. Even if you find it, you most likely will not have the ability to repair it. Use conduit this time, and in the future.
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Old 09-28-2009, 09:14 AM   #12
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Underground short on exterior lighting


There was an original GFI right at the house, the distance from there to the first light is about 40 feet and the total of buried cable would probably be about 400 feet.
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Old 09-28-2009, 11:16 AM   #13
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Underground short on exterior lighting


Quote:
Originally Posted by frustratedhalf View Post
There was an original GFI right at the house, the distance from there to the first light is about 40 feet and the total of buried cable would probably be about 400 feet.
With 400' the GFCI should see about 2 mA of leakage. You can check this with a low wattage 120v incand. lamp and a voltmeter. At this low leakage the GFCI should take a while to trip, or not (see fig. 6.7, below)
http://books.google.com/books?id=NKs...ime%22&f=false

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Old 09-28-2009, 02:00 PM   #14
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Underground short on exterior lighting


Frustrated, Thanks for hanging in there and answering questions.
Correct me if I'm wrong, You have:
• About 400’ of UF buried cable >2’ deep, feeding 3 Light posts, now trips a GFCI

From your post’s, as I see it:

• You do not need a GFCI to feed the buried UF cable
• GFCI’s are not required for yard lights per se.
• GFCI’s are needed for people protection, not for lights.
• GFCI protection is required for all yard receptacles

I am no expert on the code, but if I’m wrong on this, we’ll hear soon as there are some real experts on this Forum that know tons more than me.
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Last edited by PaliBob; 09-28-2009 at 02:19 PM.
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Old 09-29-2009, 11:31 AM   #15
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Underground short on exterior lighting


Quote:
Originally Posted by PaliBob View Post
Frustrated, Thanks for hanging in there and answering questions.
Correct me if I'm wrong, You have:
About 400 of UF buried cable >2 deep, feeding 3 Light posts, now trips a GFCI

From your posts, as I see it:

You do not need a GFCI to feed the buried UF cable
GFCIs are not required for yard lights per se.
GFCIs are needed for people protection, not for lights.
GFCI protection is required for all yard receptacles

I am no expert on the code, but if Im wrong on this, well hear soon as there are some real experts on this Forum that know tons more than me.
.
Bob,
It is correct that you do not need GFCI protection for outside lights. GFCI protection is to protect you, not light fixtures. However, a combination of receptacles and lights on the same circuit would require GFCI protection.
I agree it does not seem right as you must change bulbs and touch fixtures too. If you wanted to put outside lights on GFCI, there is no reason why you could not do it.

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