Fault Finding a Pool light circuit

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Old 04-20-19, 04:33 PM
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Question Fault Finding a Pool light circuit

Hi

We have a pool/spa with lights in each. High power halogen types. The lights are turned on by a wall switch. They used to often trip the breaker while turning on, but would usually come on 2nd time. A while back though, they stopped completely, the breaker permanently tripping.
I replaced the GFCI in the distribution panel as I suspected that, but it still had the fault.

I started isolating the wires, first to prove the GFCI in the panel was ok (it was).

I then started checking the wiring in the wall switch box. That all looks ok, but it's ALL just hot wires, there is no neutral in the box.

Then I looked in the wiring box next to the pool. No shorts etc. Just a few spiders.

Poking around with my meter I discovered that the neutral wire in the wiring box reads HOT when the pool pump circuit is live. It's a fluctuating voltage, but reaches 100V or so. The same wire traced back to the main distribution panel is HOT too, as expected. I doubt this is a coupled voltage? The wire is not labelled as a second live wire in any box, and I thought the lights were usually 110V anyway.

Any tips on fault finding the problem? I'm an electronics engineer but don't work in this area - I'm a microprocessor guy.

Thanks
Marc
 
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Old 04-20-19, 04:38 PM
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It's easy offering help when the wiring was done properly.

You are describing an open neutral but if that was the case the pump wouldn't be running either.
Is the pool pump 120v or 240v ?
The lights are always 120v or low voltage.

When a GFI that protects a pool light trips.... the problem is 99.9% at the light.
 
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Old 04-20-19, 04:41 PM
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With the power off and the neutral disconnected at the panel measure for resistance to ground. any resistance less then 4 meg is probably a leakage current tripping the GFCI.
You will get resistance hot to neutral from the bulbs
 
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Old 04-20-19, 05:13 PM
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Thanks for the fast responses.
JOED - with it all turned off I measure greater than 20Meg from distribution neutral to that wire.
PJMax - the pump is 240V and uses wires from two different breakers. Light is directly powered, so 120V

If I reconnect the live/neutral wires into the GFCI, but keep them disconnected in the poolside box I'd expect to be able to flick the switch on, but it trips straight away.
 
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Old 04-20-19, 05:25 PM
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OK more info... I reconnected the GFCI to the live and neutral wires for the lights.

If I turn OFF the pool pump breakers then the light GFCI DOES stay ON.
But when I turn on the pool pump breakers the GFCI for lights trips straight away.
 
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Old 04-20-19, 05:30 PM
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Hi, I will bet itís the fixture, can you isolate the conductors going to the fixture at the junction box, then see if the GFCI will reset.
 
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Old 04-20-19, 06:34 PM
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OK more info. I discovered that if the pool pump breakers are OFF, the pool lights both work. Shining bright.

It's as soon as I turn the pool breakers on that the GFCI lights trip.

There is an extra junction box for the pool pump so I'll tackle that next.
 
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Old 04-20-19, 06:43 PM
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It sounds like the light power is being shared with one of the legs of power to the pump.
 
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Old 04-20-19, 09:41 PM
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I suggest you repeat the resistance test to ground on the disconnected neutral that JOED mentioned, but with a load placed from one of the pump motor lines to ground (with the pump breaker off). I suggest using a load like an incandescent lamp to limit the current in case some other breaker is powering the pump line. If the resistance goes down noticeably, such as below the 4 Meg mentioned by JOED, then there is unwanted leakage (or even maybe a short or misconnection) between the lighting and pump circuits.
 
 

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