Pool Light Tripping GFCI

My Pentair light in my inground pool worked fine last summer. I had the liner replaced this winter, and the light has not worked properly since. We can turn the light on, and it will work for a while, but after some period of time between 5 and 15 minutes, it will trip the GFCI. If I then reset the GFCI and turn the light on, it will flash and go off immediately.

I don't know if this is relevant, but after installing the liner I was losing a small amount of water. The installer returned and sealed a leak at the back of the light niche with epoxy.

I did have some moisture inside the light fixture, which was the first hypothesis for what was causing the problem. I replaced the gasket, and there is now no water in the fixture, but the problem persists.

Thanks for any help.

I'm making an educated guess on this. I assume the light is an incandescent that throws off heat. I'm thinking if there is moisture in the fixture, when you turn on the light you're getting condensation somewhere other than the light and socket and if there is any exposed wire that could trip the GFCI. Something related to the lamp, socket, or the housing heating up. If you can completely disconnect the light you can measure the resistance to ground and see what it is. Should be infinity or way into the megohm range. May just try replacing the GFCI first because sometimes they do go flaky and become overly sensitive. If you're not familiar with making resistance measurements let us know and we'll walk you through. Can get a low cost V-O-M (Volt-Ohm-Milliamp) meter at Radio Shack in the $20 range.
Al

Thanks, Poconos. A friend came over today who is much more adept at this things than myself. He read your note, and also contacted a friend of his who is an electrician. The electrician wrote this note:
"Based on when it shorts it means the wire it crimped at some place (could have happened when the wire was removed and put back in during the resurfacing of the pool) or is corroding in a spot, causing a higher amount of resistance in the line, which trips the breaker. So, the only way to fix it is to locate the crimped wire, and cut it out."
My friend checked the resistance, checked the wires that are not inside the tube going from the breaker box to the pool, dried out the fixture once again more thoroughly than I had done myself, and disconnected a second wire attached to that circuit (which was for an exterior light above the pool that has not worked since before we bought this house 8 years ago). Put everything back together . . . and the light stayed on for 20 minutes, longer than ever before this season, but still eventually tripped the GFCI.
I guess replacing the GFCI would be the next step, right?

Jonboy --- If you are looking for your post, I started a new thread for you.

http://www.poolforum.com/pf2/showthr...-Tripping-GFCI

A high resistance in a wire won't cause a GFCI to trip. Yes, a wire could be crimped and damaged but ANYTHING that causes leakage to ground should trip a GFCI. That could be bad or old insulation on a wire or dampness that has gotten into a crack in old insulation and other things. When your friend measured the resistance to ground what was the reading? Also got a question....120 volt lamp? If it's a low voltage lamp then there is a transformer in the system. Yes, next step is replace the GFCI.
Al

Al:
Thanks for your input. On Saturday we spent a while testing matters - and discovered a strange source of the problem. The bulb has a spot where the reflective material is absent. It so happened that that "hole" in the reflective coating caused light and thus heat to be aimed right at the grounding spring. By pulling out the light receptacle slightly, we are able to move the position of that hole enough so that the light no longer trips the GFCI. Clearly a temporary fix - I'll replace the bulb when I open the pool next spring. BTW, this is 120V, 500w lamp.

I've been away for a few days. Crazy but at least you found it. Good detective work.
Al