GFCI tripping for exterior post lights controlled from a dimmer inside home

[Robert B Zaccaro]

I have a friend who has post lights in back yard near pool. they are controlled by a dimmer switch inside the house. When the dimmer is at full brightness or the dimmer is replaced with a standard switch, the GFI trips. When the dimmer is at approximately 75% and showing 95 volts at the post lights, the GFI won't trip. The wiring installation is horrible and I have already corrected some issues but this remains. I am going to do more testing but I wanted to know anyones thoughts on the information I have so far. Thank you!

 

[kwired]

Ground fault in the circuit, but does't "leak" enough current to trip the GFCI until effective voltage reaches a certain level?

Are the lights incandescent, LED or other electronically driven light sources? Those electronically driven types may not play so well with a dimmer and a GFCI and that could be the problem, if so try at least temporarily using incandescent lamps and see if that makes the issue go away.

 

[Another C10]

post lights in back yard near pool. they are controlled by a dimmer switch inside the house

My opinion would be , it would be more practical having the dimmer switch that feeds the pole light being protected by a GFI. I've never considered or would attempt to put a GFI on a dimming function. But that's me,

 

[Little Bill]

My opinion would be , it would be more practical having the dimmer switch that feeds the pole light being protected by a GFI. I've never considered or would attempt to put a GFI on a dimming function. But that's me,

I don't think he is trying to "dim" the GFCI. The circuit is protected by a GFCI and is tripping when either the dimmer is at full brightness or a regular switch is used.

 

[Another C10]

I don't think he is trying to "dim" the GFCI

Sorry, read that wrong. I was gonna say ..

 

[hillbilly1]

Since you say post lights, divide and conquer, probably a damaged cable underground. Disconnect at first pole, send full voltage to the line. If that holds, reconnect and disconnect at next pole, and so on. This will give you an idea what part of the circuit is the issue. A megger would be handy to test the integrity of the wire. Could also be moisture in one of the lights, so disconnecting them one at a time is another option.

 

[Another C10]

I'd probably try putting a normal breaker on the circuit, put an amp probe on the hot then the neutral see if there is an unbalanced reading, if not then try a different GFI Breaker or try what was mentioned in post #2 or post #6

 

[kwired]

Could also be moisture in one of the lights, so disconnecting them one at a time is another option.

I'd probably try putting a normal breaker on the circuit,

If it is just some moisture in a bad place, simply energizing for a bit without the GFCI interrupting too soon may very well "burn it out" and then it will work again on GFCI.

 

[LarryFine]

When the dimmer is at full brightness or the dimmer is replaced with a standard switch, the GFI trips. When the dimmer is at approximately 75% and showing 95 volts at the post lights, the GFI won't trip.

There is a fault, and the GFCI doesn't detect it until its internal electronics receive enough voltage.

A GFCI should not be on the load side of a dimmer.

Added: I read more, now we need to find out what order the devices are in.

 

[Little Bill]

There is a fault, and the GFCI doesn't detect it until its internal electronics receive enough voltage.

A GFCI should not be on the load side of a dimmer.

The GFCI is not on the load side of a dimmer, the GFCI is feeding the dimmer. The OP said that it will trip even with a regular switch.

 

[Another C10]

A GFCI should not be on the load side of a dimmer.

That's the misunderstanding I had, apparently the pole lights and dimmer are fed from a GFCI Breaker.

 

[winnie]

Actually, from reading the OP, we don't know the order of the devices. The installation _should_ be GFCI protection then dimmer then lamps, but it could be dimmer first.

If it is dimmer first, then my guess is that there is a ground fault, but the GFCI doesn't function when dimmed.

If the installation is properly GFCI first, then my guess is that it is a high impedance fault which doesn't leak enough current until at full voltage.

-Jon

 

[Jraef]

Actually, from reading the OP, we don't know the order of the devices. The installation _should_ be GFCI protection then dimmer then lamps, but it could be dimmer first.

If it is dimmer first, then my guess is that there is a ground fault, but the GFCI doesn't function when dimmed.

If the installation is properly GFCI first, then my guess is that it is a high impedance fault which doesn't leak enough current until at full voltage.

-Jon

Goid point actually. Looking at a couple of on line spec sheets, it appears that GFCIs are designed around 115VAC +-10%. 95V is about -17.5%, so out of tolerance. If the GFCI is downstream of the dimmer, that might explain it. The OPs description is a little ambiguous. He never says it is a GFCI breaker (which would put it ahead of the dimmer), it might be a GFCI in an outdoor outlet controlled by an indoor switch and they tapped off down stream of the outlet to run the lights, putting the GFCI in series with the dimmer when the switch was replaced. So with the switch back in, the GFCI gets full voltage and trips on the down stream GF, but with the dimmer at 82.5. % voltage, the GFCI shuts down and fails to trip.

GFCI Variable Voltage Range? | Leviton Online Knowledgebase

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[Robert B Zaccaro]

I have a friend who has post lights in back yard near pool. they are controlled by a dimmer switch inside the house. When the dimmer is at full brightness or the dimmer is replaced with a standard switch, the GFI trips. When the dimmer is at approximately 75% and showing 95 volts at the post lights, the GFI won't trip. The wiring installation is horrible and I have already corrected some issues but this remains. I am going to do more testing but I wanted to know anyones thoughts on the information I have so far. Thank you!

The lamps are incandescent and the dimmer is on the load side of the GFI. I am going to break apart the circuit and narrow down the location as much as I can and because there are a number of splice points, I should be able to get it close. I wasn't sure if anyone had seen a GFI operate this way before. Unfortunately the original work done here was by the previous home owner. Also the pool guy thought he was an electrician because after he damaged wiring running a pool return line, he proceeded to put LB's and junction boxes under ground to repair his mistake. Unfortunately my friend bought the house not knowing the issues. Based on one of the replies with the specs of the GFI, this leads me to believe the circuit is functioning properly and there is a leak but when the lights are dimmed, the voltage falls outside the operating specs and the GFI doesn't trip. Thank you for all of your posts, this has been very helpful. I will reply to this string when I make the repair and let you know what I found.