GFCI trip for no obvious reason


Hello,
I'm having a problem with a GFCI outlet faulting for no "good" reason. The run extends from the garage down beside the drive way, buried about 8" depth to a light fixture on a brick column near the street. The wire was 10 wire approved for direct burial. On the column are two boxes, one for an electronic eye ( dusk to dawn switch ) and the other is an outlet with a protective cover. I checked both boxes to make sure they are waterproof and not leaking. If I unwire the run that goes to this light, then I never get a GFCI fault. This same configuration is also in use on the other side of the drive, and has zero problems with faulting.
The only "thing" that I can think of is that somehow this wire that was approved for direct burial is somehow causing the problem. Perhaps there is a nick in the wire insulation that is causing the fault. It's most strange because sometime I'm troubleshoot the problem and be fault free for several hours. Then, other times, it will fault within 10 minutes. Both on the same sunny afternooon.
Any ideas??
Thanks,
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I think you hit the nail on the head. A rock can cut into UF cable and cause intermittent problems depending upon the moisture in the ground

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Thanks to all for the FAST response.
I know it's not the GFCI, I tried replacing that as well, just to rule it out.
Looks like I'm down to doing a physical inspection of the wire. I was hoping against hope that it wouldn't come to that. I thought maybe there was some way to use a multimeter to measure the resistance to see if this really was the case.
I think the next move will be to strech some wire I have in the garage and see if I can go a whole sunny day with a fresh run of wire without faulting. If so, I think I'll have to rent the trencher again and run fresh wire packed in sand to help keep the rocks away.
Does anyone know why direct burial wire can't be run in plastic conduit? I would run it this way and bury everything to keep this from happening again.
Thanks a million!
RBM (remove this) wrote:

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I routinely run it in PVC, and for that reason exactly

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wrote:

Double and triple check any advice given by RBM. He's a bit of a nut case. He might post something correct, but he isn't someone trustworthy. That's for certain.
CWM
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Charlie Morgan wrote:

RBM probably posts more on electrical subjects than anyone else, and his posts are consistently very good.
-- bud--
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snipped-for-privacy@gmail.com wrote:

Since you have to dig it up anyway dig the trench the required full foot this time and if you want to avoid the nick problem install rigid PVC conduit.
--
Tom Horne

"This alternating current stuff is just a fad. It is much too dangerous
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GFCIs trip at 5 milliamps. It doesn't take much moisture or crud to cause that much of a fault current (from hot to ground). The GFCI might be bad ... I have see that more than once.
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