Note that this is in Thailand where there are no rules.

My home has a main breaker which includes a GFCI. Recently the breaker has started to trip when it gets cold. (This is Thailand. Cold means around 20ºC or about 68ºF).

I have isolated this to one circuit. When I turn that circuit off, the main no longer trips. I have tried unplugging everything on that circuit and turning all the lights off. It still trips at night when it's cool. The next morning when I turn that circuit back on, all is well. If the nights are warm, the breaker doesn't trip.

Any ideas?

Breaker Box

Horrible Wiring

  • Two possibilities: a heater thermostat that you missed, and condensation. If it's humid and the temperature drops, water could be condensing, e.g. in a junction box, particularly one on an outside wall or bathroom. Commented Jan 3, 2021 at 3:46
  • Is it a GFCI or an RCD or GFPE? The difference is 5ma vs 30ma trip. 5ma is awfully small for a whole house, and will tend to nuisance trip. That's why Europe uses 30ma. However 30ma is inadequate for personnel protection. Commented Jan 3, 2021 at 22:33
  • Also is the booger-snot of wires gushing out of that uncovered box the normal state of affairs? That box looks violently overfull, and the cables and conduits are not properly fitted to it. Since this looks like North American style wiring methods in an unimproved space, could you add some more or bigger boxes to maybe seal it up? Commented Jan 3, 2021 at 22:42
  • 1
    It's an RCBO. Photo: RCBO. -- The attic had no conduit. Just insulated conductors lying all over the place. I made them rip it out and use conduit. What you see is just before they finished. The conduit is now properly fitted and the boxes covered. All of the outdoor sockets had ground wires about 3" long - just long enough to disappear down the conduit where they hoped you wouldn't look. I made them fix that as well. Also, there was no ground for the house. I had them buy a copper rod, drive it in and connect it. - This is Thailand. There are no rules.
    – Buadhai
    Commented Jan 4, 2021 at 2:21
  • More likely:There are rules, but little enforcement, and likely what little enforcement there is can be bypassed for a small fee. Commented Jan 4, 2021 at 21:57

1 Answer 1



Some part of the circuit - a receptacle, switch, or junction of some sort - has a very minor ground fault. It is OK when warm and dry. When the air cools at night down to the dew point, water condenses. It bridges the ground fault and enough current flows through to trip the GFCI.

With one quick search, I found a current dew point in Bangkok of 60 F. It will vary a bit by day, time and location, but that isn't far off from the 68 F you noted.

The only solution is to check every single junction in the problem circuit. In particular look for any bare wire (except grounds), loose wire nuts or signs of corrosion. You can rule out, initially, any light fixtures, since you have the problem even when they are off. However, wires often go through those boxes on the way to other parts of the circuit, so the problem may be there too. You may have multiple sources of the problem, though since all your other circuits are OK, there is a good chance there is just one problem area.

  • 1
    This is probably the case. Thanks so much. So, first step would be to check every outlet box and light switch box. That I can do easily. The light fixture boxes are in the attic which would be a lot harder for this old man. I'll have to get someone to do that. I appreciate your taking the time to write such a comprehensive reply.
    – Buadhai
    Commented Jan 3, 2021 at 5:40
  • 1
    I may have found it: outlet photo
    – Buadhai
    Commented Jan 3, 2021 at 6:06
  • Yikes! I would definitely recommend replacing that. Commented Jan 3, 2021 at 6:25
  • Yep. On the list.
    – Buadhai
    Commented Jan 3, 2021 at 6:50

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