Outdoor Christmas lights tripped GFCI after rain


Old 12-17-15, 08:36 PM
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Outdoor Christmas lights tripped GFCI after rain

Last Sunday, I put up about the same amount of lights in the same manner as I have for about 15 years. (Using the mini-incandescent bulbs.) As I finished, the GFCI tripped and would not reset. I also discovered that the timer I was using had gotten very hot and partially melted where the 3-outlet plug was plugged into it...maybe that tripped the GFCI. I found the reason it melted is likely due to it's 10 amp rating while I know the lights are pushing the 15 amp limit of my outside GFCI circuit.

The GFCI, original with the 22 year old house would not reset. Lately the reset button didn't really feel like it was clicking like it used to, and now it also wouldn't reset the circuit. I replaced it with a new 15 amp GFCI, and bought a 15 amp timer, and everything worked fine for four nights. Then it rained today, and the GFCI tripped. I tried drying out all connections to extension cords and wrapping them in plastic wrap to keep them dry in case that was causing a short. Still wouldn't work. I isolated the section that was causing the trip, which consisted of 4 separate extension cords each feeding several light strings to try to figure out which one was shorting out. I found that each one worked when plugged in separately, and a couple would work together, but for most combinations, plugging in the second feed, and definitely the third would trip it again.

I'm confused about what is happening. I figure the total load is less than 15 amps since the circuit breaker is not tripping, and did not trip when all lights were working in dry weather. My understanding of the GFCI is that it will trip upon detection of a short or ground. But since every section will work individually, doesn't this mean none of them have a short or ground? Then why does the GFCI trip with all sections plugged in, but not just one or two? What about the rain is causing the GFCI to trip with everything connected, when it worked fine when it was dry? If the rain is causing a fault, why would each circuit still work individually while wet?

Any thoughts for how to fix the problem with my current setup? And might it help in the future to upgrade to a 20 amp breaker for my outside circuit?

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Old 12-17-15, 08:47 PM
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A 20A circuit would help handle the load but it won't change the GFI tripping.
You have excessive leakage from the hot side of the circuit to ground. It can leak thru wet shrubbery.... extension cords on the ground. Water is conductive.

It isn't the amount of current draw as you add strings..... it's more leakage to ground.

My neighbor is a Christmas lighting guru. He went from 6) 20A GFI circuits to no GFI circuits.
I didn't recommend or condone it but he had GFI's tripping constantly.
Old 12-17-15, 10:29 PM
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Each set can have a slight amount of leakage that all together is enough to trip the gfi. The moisture only makes things worse.
Old 12-19-15, 10:01 AM
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I wonder if the new GFCI I just put in is more sensitive than the original, 22 year old one? If so, is it possible to get a GFCI with a higher current threshold to trip it?

Pete, what is the safety issue between using a GFCI vs. non-GFCI for Christmas lights. Wouldn't the breaker trip on a short to ground also, say if a heavy rain caused a plug to be in a puddle or otherwise cause a short between the leads in any of the several dozen light string plugs? Probably a dumb question, but I'm primarily a mechanical guy with just enough electrical knowledge to be dangerous.
Old 12-19-15, 10:26 AM
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Wouldn't the breaker trip on a short to ground also, say if a heavy rain caused a plug to be in a puddle or otherwise cause a short between the leads in any of the several dozen light string plugs?
Rain water is conductive, but not highly conductive. That means that someone could be severely shocked or killed before the breaker would trip. GFCI trips is something to be expected with cheapy Christmas lights.
Old 12-20-15, 09:08 PM
Join Date: Oct 2015
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Are any parts of the lights hung on grounded metal items? If so, capacitive coupling between one side of the line and ground could occur through the thin plastic of the light wires.

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