Re: Jonboy's Pool Light Tripping GFCI

I also have a Pentair light: "Amerlite" ig pool light, 500w, 120vac. It was working fine until:
I noticed the pool supply panel was not protected by a GFCI, so I installed a new GFCI breaker in place of the breaker that supplied the pool panel. The pump fed by that panel works fine, the outlet fed by that panel works fine. But, the light trips the GFCI immediately when I turn it on.
I disconnected the light at the box about 6' from the pool, turned the light on, and it did not trip, so I know its not in that section of the wiring between the supply box and the box by the pool.
I took the pool light assembly out onto the deck to visually inspect it and it had no water or vapor, that I could see, inside the assembly, but still tripped the GFCI as soon as I flipped the switch (no flash, nothing, immediate trip).
I measured the resistance as suggested, and it measured 500k-600k ohms across the green to white, and across green to black. It measured 0 ohms across the black to white. I then took the bulb out and got the same measurements across the green - white and green - black, but infinite resistance across the black to white.
I considered a faulty bulb, so I replaced it with a regular household bulb (60w). It tripped immediately.
Do I just need to bite the bullet and buy a new light assembly? Please tell me I'm overlooking something.

The measurements look good and the GFCI shouldn't trip at 240 microamps which is what the 120V with a 500K load represents. From what I've read they should trip around 2 ma or less depending on the class of GFCI. Is the green ground wire tied to the light housing like it should be? I'm also wondering if you're running into a situation where the resistance shown by the VOM, which measures resistance with a low voltage, is not what the leakage resistance is with 120 volts on the circuit. That's 170 volts peak. Think of an extreme case where you apply a high enough voltage and any insulation will eventually break down. So, the trick is to somehow measure the leakage current in real life with 120 VAC applied. If your VOM measures AC current you have it licked. Power the light without the GFCI and open the green ground wire, insert the VOM and measure the AC current flowing in it. Should be ZERO. Another way if your VOM doesn't measure AC current is to open that green again and insert a 1K resistor, or anything reasonable. Measure the AC voltage across the resistor. 1 ma would equate to 1 volt across a 1K resistor. E=IR. I think I would prefer measuring this way as all VOMs don't measure AC current and although they should be protected against over-current, less of a risk in damaging the VOM in the event of a short.

Sounds like you know what you're doing but I have to say it anyhow, use common electrical sense when doing this stuff so you don't light yourself up and it's always good advice to have someone with you.

Hope this helps.
Al

Edit: Thinking a little more, that 500K you measured should be more like infinity or at least in the several megohm range. I think you do have a leakage problem that shows up with full voltage applied like I stated above.
Al