lamp post wiring trips GFI

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Old 05-20-10, 06:36 AM
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lamp post wiring trips GFI

I have a decorative lamp post that will often trip the GFI recaptacle after long periods of rain. The lamp circuit isn't usable for a few days after heavy rains until things dry out. Some how moisture must be getting to the wires. There is outside cable that runs underground between the garage and lamp post (maybe 8'), contained within an electrical pvc conduit. The conduit is sealed until it terminates inside the lamp post. Conduit runs horizontally through a hole in the pole about a foot below the surface. The lamp post is set in concrete a couple inches below the electrical hole. The surface is treated with stone mulch.

I'm assuming water must fill within the lamp post and submerge the cable? Wouldn't the cable need to be damaged to be affected by the water? Water must seep through the hole in the lamp post until it submerges the electrical cable. Is a fix to extend the sealed conduit vertically in the lamp post, or have the cable enter the post closer to the surface?

Has anyone run into a similar problem?
 
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Old 05-20-10, 07:32 AM
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What kind of cable? Does the conduit run for the whlole run?
 
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Old 05-20-10, 08:41 AM
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Originally Posted by kidbat View Post
I have a decorative lamp post that will often trip the GFI recaptacle after long periods of rain.
Are you sure it's the lamp and not moisture accumulating in the GFCI receptacle or another box on this circuit?

Wouldn't the cable need to be damaged to be affected by the water?
Assuming the proper type of water-proof cable was installed, it would need to be cut or nicked to be affected by the water. It's also possible someone put the wrong type of cable in and it has rotted.

Is a fix to extend the sealed conduit vertically in the lamp post, or have the cable enter the post closer to the surface?
No, regardless of how well sealed all outdoor conduits collect water through condensation anyway. The problem is more likely at a connection in the circuit than in the middle of a cable run. Check the junction boxes at either end for moisture, check the lamp fixture, the lamp junction box, etc. Maybe a gasket or caulking has a leak and is letting water in there.
 
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Old 05-20-10, 11:55 AM
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The cable is outside use cable NM (I believe type 14-2). It's gray in color and was definitely the outside type of cable. A relative helped me install about 9 years ago.

There is an outside outlet connected to this same GFCI, but it's under an awning and very seldom gets wet. I couple times its tripped from water which was sprayed from a hose, but rain can't normally reach the receptacle. The GFCI is inside the garage.

They only reasonable place for moisture to reach the circuit is between the outer garage wall and lamp fixture. I attached a schematic of the setup.

If I'm clear, the electrical conduit doesn't necessarily need to protect from moisture, correct (only for digging protection)? The cable sheathing should be doing this, right (undamaged cable should be ok even if surrounded by water)?
 
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Old 05-20-10, 01:34 PM
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Originally Posted by kidbat View Post
The cable is outside use cable NM (I believe type 14-2). It's gray in color and was definitely the outside type of cable.
That should be UF-B "Underground feeder". Your description sounds like the correct type.

There is an outside outlet connected to this same GFCI
I would consider this one as a possibility. It takes very little moisture to trip a GFCI. Just the humidity from the rainy day can cause condensation build-up in the box. Also it might help to duct-seal or caulk the penetration where the cable runs from the garage into the outdoor box/conduit. Sometimes the mixture of conditioned inside air causes condensation in the boxes that are exposed to the outside.

They only reasonable place for moisture to reach the circuit is between the outer garage wall and lamp fixture. I attached a schematic of the setup.
The drawing looks like a correct installation.

If I'm clear, the electrical conduit doesn't necessarily need to protect from moisture, correct (only for digging protection)?
Correct.

One other thing to consider: does the lamp have a photocell that might be leaking?

To solve the problem, my first step would be to open up all the boxes in the circuit and inspect for moisture, if none is detected, try replacing the GFCI receptacle, if it still persists then pull new conductors which shouldn't be too big of a deal since you have conduit all the way.
 
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Old 05-20-10, 02:50 PM
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I was wondering about condensation possibly inside the pole. If water perhaps sits within the sump (below the port hole for the conduit), then could the inside of the pole become very humid and wet. There's no air flow and maybe a couple inches of water trapped in the bottom of the pole, since the pole is set in concrete. This problem will occur anytime of the year when there is a lot of rain (summer or winter in WI).

There is a problematic photocell, which pushed me to resolve this problem as well. I'm not that experienced with electrical matters, but I would bet against the leaking photocell or box. I'll still seal the outside outlet and replace the photocell, but the GFCI will typically stay tripped for several days after a lot of rain (seems to correlate very closely with ground drying out). During a huge soaker I cannot reset GFCI, after the rain it will stay on for a few minutes until it trips, finally after several days or week it will be fine.

Thanks for the good information. At least I know the installation isn't flawed. I don't think the cable is damaged but I will consider pulling a new cable if sealing outlet box and photocell don't seem to help.
 
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Old 05-20-10, 04:40 PM
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I will outline very simple way .,

First thing is check the recetptale to see if any moisture show up.

Next step is check the GFCI recepetale to make sure it dry inside the junction box.

If above two items are clear then go next step.,

Check the post luminaire for any corroioson or loose connection if they are good then try the photocell if any moisture show up.

If all are good then it possiblty the UF feeder cable can get nicked due I know you mention a conduit for protection as far we know about the frost can shift a bit so that one possiblty it may got nicked but which spot that is a big question so it will be wiser to run new cable. unless you get a hold of electrician to have underground tracer to find a bad splice.

When you install the cable that time did you have rocky soil or just standard clay soil if rocky it may punchure it.

Merci,Marc
 
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