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I have an outdoor outlet in a covered patio ceiling that is labeled in my breaker box (in the garage) as a dedicated 20A XMAS lights circuit. The GFCI trips non-stop on rainy days, sometimes after a few hours. often just within minutes.

Order of operations:

Possible issues?

  1. Could it be my extension cord is too long, even though I got a beefy 10/3?
  2. Is it a problem that my extension cord sits on wet concrete, even though it's SJEOOW (weatherproof/water resistant)?
  3. I have tried plugging in one string at a time and each string still causes the GFCI to trip. These were new strings purchased 2 weeks ago.
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  • Buy all the waterproof gear - more expensive though.
    – Solar Mike
    Commented Dec 6, 2023 at 6:35
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    All the equipment outlined above is waterproof/outdoor.
    – Harry
    Commented Dec 6, 2023 at 6:39
  • Stupid question: is your GFCI okay? Sometimes when they go bad they trip too easily. I've gotten my lights to work in the past by literally just plugging them in to the GFCI and using them.
    – KMJ
    Commented Dec 6, 2023 at 6:42
  • Waterproof to what standard?
    – Solar Mike
    Commented Dec 6, 2023 at 7:12
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    Have you tried a different GFI outlet with experiment 3? Have you tried any different model of string lights or even a lamp with the offending outlet? Experiment 3 is instructive. It's either the outlet or the design of that string.
    – jay613
    Commented Dec 6, 2023 at 14:04

3 Answers 3

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To answer just question 2, a very long extension cord should not trip a GFI. If it's damaged, cracked through the outer and inner insulation, that might do it. If its indicator light is leaking to ground, that could also do it and that might be intermittent since its normal power might be below the GFI's threshold.

The extension cord is no different to all your string lights. If there is an actual ground fault in it, that would be a cause. You seem to have eliminated it in experiment 3.

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Move indoors to continue the experiments:

  • Test the extension cord:
    • Plug the extension cord into a GFCI (in the kitchen maybe) does it trip the outlet on its own?
    • Plug in a lamp of some sort to to the extension cord & turn it on, does it trip the GFCI?
    • Toss the middle part of the cord into a bathtub full of water (do stand back...), does it trip the GFCI?
    • If none of these happen, your extension cord is fine.
  • Test the lights:
    • Using the same GFCI (protected) receptacle, test each string of lights on its own. If any one of them trips, that one individual string is bad, chuck it, return it, whatever.
    • Once you've tested them individually, start plugging them in in series to see if you reach a point where the GFCI trips. It's unlikely that the additional load will cause issues, but you never know.

If none of these tests cause a GFCI trip in a known dry environment, then you've eliminated half the problem (the cord & the lights). The other half (the "Christmas light" circuit and the waterproof connection protectors) needs testing.

  • Test the "Christmas light" GFCI

    • Plug the lamp from the above testing into this outlet & turn it on, if the GFCI trips, you've got a bad outlet or breaker.
  • Test the waterproof connectors

    • Plug the extension cord back into your indoor GFCI
    • Plug a string of lights into the cord
    • Put a waterproof connector over the plugs
    • Stand way back and toss it into the bathtub filled with water.
    • If the GFCI trips, that waterproof connector isn't as waterproof as you thought.
    • Our house was under DIY residing last winter and we had scaffold up all winter long. For fun, I put up Christmas lights on the scaffolding. I wrapped the plugs in a plastic bag, put a zip tie around it and put the open end of the bag (knowing it wasn't "sealed") down. I had zero issues with water ingress or breakers tripping. We had rain and snow through December & January. i.e. I think your waterproof plug protectors may be overkill...
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My suggestion -- not that I do the aircraft-beacon lighting thing -- would be to see if low-voltage lights are available and keep the power supply dry. Now that everything is LEDs, that should be an available option...

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  • I've not seen any low-voltage Christmas lights. To be fair, I've not gone Christmas light shopping in a long time, but AFAIK, they're all designed to run off of 120VAC.
    – FreeMan
    Commented Dec 6, 2023 at 15:23
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    5V, 12V, and now 24V addressable (multi-color) LEDs, in strips, "bullets," squares, and pucks are now very common amongst Christmas lighting enthusiasts. They run from an AC->DC voltage converter that does use line voltage as an input, but the LEDs run on low voltage. Commented Dec 6, 2023 at 15:43
  • Ah, fair point, @FredricShope. I guess it's not about Christ any more but about the show. I keep forgetting that...
    – FreeMan
    Commented Dec 6, 2023 at 15:46
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    Many of the standard looking lights you buy now are low voltage, but include an adapter, often times in-line on the cord. So they appear to be 120VAC.
    – longneck
    Commented Dec 6, 2023 at 15:54
  • If it's LEDs, it's almost certainly low DC voltage with an adapter. The question becomes how many lights one adapter can drive, or do you need more adapters or a bigger adapter. Check the specs; some manufacturers know people want to do this and explain how. (Probably not the cheapest kits, though; they're cheap because they are designed to be Just Barely good enough.)
    – keshlam
    Commented Dec 6, 2023 at 23:13

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