GFCI Breaker Tripping Spa Light

tbird355August 8, 2010

I have a problem with GFCI breaker tripping on a Spa (hot tub) light. Here's the details.

This is a built-in spa (not premanufactured) built 20 years ago. There is a underwater Sta Rite (Pentair) enclosure built into the gunite wall. Installed in that niche is a Sta Rite 120 volt 250 watt fixture. The fixture is fed by a 16/3 captive cable that runs in a conduit from the niche to the equipment room on the other side of the wall. The 16/3 cable is connected via wire nuts in a jbox to 3 14 gauge stranded cables (black, white, green) in a conduit from the subpanel. The fixture is alone on a 20 amp GFCI breaker in the spa subpanel. The GFCI breaker trips as soon as it is set. Until recently, the light had been working fine. I swapped in a new breaker with the same results. Given that the fixture is 20 years old, I installed a new Sta Rite fixture. It also trips the breaker immediately.

I have tried a number of things to try and locate the problem but with no success. I took the new fixture and captive cable out of the spa and conduit and connected it directly to the breaker. That worked fine. With the fixture and cable back in place, I disconnected the ground wire in the jbox. The strange thing is that, with the ground wire disconnected, the breaker did not trip as long as the fixture was out of the water and not in its niche. As soon as the metal housing of the fixture touches the water, even slightly, the breaker trips. With the light fully installed back in the niche, one by one I disconnected the 3 wires in the jbox. With the ground wire and hot lead connected but the neutral disconnected, the breaker did not trip. The neutral connected by itself or the neutral and the ground connected caused the breaker to trip even without the light on. That tells me the fault is coming from the neutral. The problem is I can't imagine how the fault is occuring. It's a new fixture. The captive cable is new. There is nothing else on the circuit.

Any ideas?



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What about the conduit feeding the J-box underground. Is it corroded? This could possibly cause it to ground out and trip the GFCI.

    Bookmark   August 9, 2010 at 12:51AM
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You replaced the GFCI breaker. Neutral from light feeds through this breaker. Verify that is correct.
You replaced the fixture.
Only thing left is the wiring from the J-box to the subpanel.

    Bookmark   August 9, 2010 at 2:10AM
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Here's an update on this. Pentair sent a replacement fixture and it works properly. The breaker does not trip.

Bottom line was that the original fixture was slightly leaking water and therefore creating a current path to ground tripping the breaker. The new fixture we purchased had defective electronics in the overload circuitry causing it also to trip the breaker. The replacement fixture from Pentair replacing the new one under warranty worked properly.

    Bookmark   September 8, 2010 at 11:51AM
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I hate problems like this, because the last thing that you would assume wrong is that the new fixture is bad.

    Bookmark   September 8, 2010 at 11:36PM
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Problems like this are where a good ohmmeter is valuable.
I had a similar GFCI problem where it would trip immediately whenever the light was switched on. I disconnected the "hot" supply wire at the panel, and got very low impedance...0.7 ohms. The 300W bulb is about 4 ohms, so that's what it should have read. I removed the underwater fixture, disassembled, took out the bulb, and the fixture and wire, unattached to anything, gave me 36k ohms from the hot to ground. GFCI will trip with any leakage below 48k ohms. I found burn marks on the cable just behind the fixture. I'm guessing the installing electrician test ran the light before the pool was filled and it scorched the sheathing at several spots where the "extension loop" was wrapped around the fixture.

I now have to get a new fixture / cable. This time, I'll use a LED bulb.

    Bookmark   June 23, 2014 at 12:09PM
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often times if the neutral from the jbox feeds any other devices it could trip it. it should have a separate neutral.

    Bookmark   June 24, 2014 at 1:44AM
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