Issues with circuit breaker/RCD randomly tripping - Page 1
Forum section: electronics / general

author: Halcyon
author_rank: Unknown
timestamp: August 10, 2021, 10:24:13 pm
content: I'm at a loss.For two night in a row, one of the circuits that feed the power outlets to half my house randomly trips. It also feeds the gas hot water system, range hood, cooktop and outdoor IP-rated power outlets (those are under cover and have nothing connected). The breaker has an RCD built-in.On Monday night, the breaker tripped and I was unable to reset it. I went around and disconnected everything I could from that circuit but it would trip off straight away. Tuesday morning, I could reset it just fine and it remained on most of the day (with everything re-connected and operating just fine). Electrician came around yesterday and did earth leakage tests while I went around and connected everything back. Nothing. Everything showed normal.Last night came around and it trips again, same deal, unable to reset it. This time I crawl up into the roof, disconnect the range hood and also the hot water system and cooktop. Still unable to reset it. This is with absolutely nothing connected to it. On both occasions, I wasn't doing anything in particular. Just on the computer.I thought maybe water or humidity is getting in somewhere, but it hasn't been raining and it's quite dry at the moment. Besides, in the mornings it's quite dewy and moist, but the breaker is able to be reset.It's not a case of overloading either. Fully loaded, that circuit would probably be a few hundred watts at most (without the coffee machine or toaster operating).What are the chances of a faulty RCD? The electrician said it's extremely rare for it to be the cause. I am honestly scratching my head as to what it could be. I should also point out that it's a relatively new house, well under 10 years old.

author: twospoons
author_rank: Frequent Contributor
timestamp: August 10, 2021, 11:02:16 pm
content: 'Rare' is not the same as 'never'. I'd replace the breaker and see what happens, since you think you've exhausted all the other possibilities.Have you opened up the outdoor outlets to make sure nothing has crawled inside?

author: Halcyon
author_rank: Unknown
timestamp: August 10, 2021, 11:06:43 pm
content: Quote from: twospoons on August 10, 2021, 11:02:16 pmThe electrician is coming back today to replace the breaker. Even he admits in the absence of possums/mice/rats it's quite strange.I haven't opened the outdoor outlets, they look to be well sealed with silicone. I'll ask him to have a look at that today as well.

author: themadhippy
author_rank: Super Contributor
timestamp: August 10, 2021, 11:26:07 pm
content: QuoteDo they have a drain hole?

author: Halcyon
author_rank: Unknown
timestamp: August 10, 2021, 11:44:59 pm
content: Quote from: themadhippy on August 10, 2021, 11:26:07 pmNo idea, I'll check later today.

author: james_s
author_rank: Super Contributor
timestamp: August 11, 2021, 12:40:39 am
content: One of the first things I would have tried is replacing the breaker. Most of our GFCIs are built into receptacles that protect downstream receptacles but we have the type that go in the panel too and I have seen both types fail such that they start to nuisance trip. If you replace the breaker and it continues to trip, then is the time to really start digging into things.

author: Halcyon
author_rank: Unknown
timestamp: August 11, 2021, 04:06:37 am
content: Quote from: james_s on August 11, 2021, 12:40:39 amSo that's what they've done today, new breaker is in. Everything that was connected before is now on the circuit again. Time will tell whether this fixed it or not. Both times, the electrician said the "Megger" reading was perfectly fine on that circuit.

author: andy3055
author_rank: Super Contributor
timestamp: August 11, 2021, 04:29:43 am
content: Agree on the replacement of the breaker. Sometimes even if they are not bad per say, they can trip due to age related deterioration. Also, have the electrician check the lugs that make contact with the breaker (don't know the correct term) in the panel. Just a thought.

author: Halcyon
author_rank: Unknown
timestamp: August 11, 2021, 05:26:11 am
content: Quote from: andy3055 on August 11, 2021, 04:29:43 amWe don't have "lugs" here. The breakers sit on a normal DIN rail and the cables screw directly into the breaker. As long as the screws are nice and secure, it'll be a good connection.

author: Halcyon
author_rank: Unknown
timestamp: August 11, 2021, 09:31:11 am
content: Well, it wasn't the breaker. Something is still going to ground somewhere. Happens around the same time every night.

author: Vovk_Z
author_rank: Super Contributor
timestamp: August 11, 2021, 10:32:19 am
content: Quote from: Halcyon on August 10, 2021, 10:24:13 pmSo, a ghost is not a reason too.Mouses start to move at night...Have you pulled off everything from sockets?

author: Gyro
author_rank: Super Contributor
timestamp: August 11, 2021, 11:22:31 am
content: Hopefully the electrician did an insulation test on Neutral to Earth as well as Line-Neutral and Line-Earth. Neutral-Earth faults are notorious for causing intermittent RCD trips with no other symptoms.

author: themadhippy
author_rank: Super Contributor
timestamp: August 11, 2021, 11:36:27 am
content: QuoteQuoteIs there a time clock on the heating system

author: Psi
author_rank: Super Contributor
timestamp: August 11, 2021, 12:40:29 pm
content: Since your old RCD is not faulty you could reinstall that so you have two and wire half the connections to each. At least you can eliminated 50% of the items the next time it tripshm.. you said you have gas hot water, do you also have a smaller electric hot water tank as well, maybe on ripple control(It's not uncommon here to have primary gas hot water but also a smaller electric hot water cylinder in the kitchen so that hot water is available instantly.)Another intermittent option is the icemaker in the fridge door, or water cooler.

author: Alti
author_rank: Frequent Contributor
timestamp: August 11, 2021, 01:55:32 pm
content: I'd start from checking what failed.There are various types of RCBOs (if that is what you have there) and most of the designs do not indicate which out of four trips actually tripped. So you are assuming this was residual current part - what makes you think so? Because you did not turn on any loads? If that is not due to overloading but there is also a magnetic trip inside - there is no way to tell, especially when it is B curve. Then, if you have reactance there (inductor or capacitor) and you are unlucky, it is going to trip due to inrush at turn on.If that is residual current part and you have single pole circuit breakers then I am afraidthis is going to take sometime till you figure out what is going on there.

author: edpalmer42
author_rank: Super Contributor
timestamp: August 11, 2021, 05:08:40 pm
content: Have all the outlets been inspected? Maybe spiders/ants/wasps built a nest in one (particularly the outdoors ones).Has the weather been consistent while this problem has been occuring? Evening - things cool down enough to cause condensation inside an outside outlet that combines with some dust or dirt to create a path? During the day everything dries out and works fine.

author: andy3055
author_rank: Super Contributor
timestamp: August 11, 2021, 06:26:55 pm
content: Quote from: Halcyon on August 11, 2021, 05:26:11 amAre you saying both sides of the breaker are screwed on type? I know the load side is. In the US panels, the supply side is not screwed.

author: andy3055
author_rank: Super Contributor
timestamp: August 11, 2021, 07:48:35 pm
content: I just remembered this. You could be having a loose neutral in one of the sockets on that circuit. It could even be a loose live wire. But mostly I have seen a loose neutral doing that.

author: MrMobodies
author_rank: Super Contributor
timestamp: August 11, 2021, 08:10:42 pm
content: I once had a rusty pump that started to leak and it would trip the whole fuse box if the rcd for that circuit was switched back on.It was intermittent at first and everything would come back on when resetting the main RCD. Then it would just reset until I switched all the other switches off and I traced it to the boiler switch and found the pump was slowly dripping.

author: james_s
author_rank: Super Contributor
timestamp: August 11, 2021, 08:43:21 pm
content: Quote from: andy3055 on August 11, 2021, 06:26:55 pmMost places outside of North America use DIN rails just like the ones we used in our industrial equipment. The breaker clips to a mounting rail and has screw terminals on both sides.

author: TimFox
author_rank: Super Contributor
timestamp: August 11, 2021, 10:30:58 pm
content: Since you are now in winter, I would suspect a funny connection or short that is temperature dependent, if the fault always occurs during darkness. Possibly a tight wire that shrinks, or something that moves and is not there when the electrician does his insulation test during daylight. (Similar to why low-battery-alarms in smoke detectors always go off at 3 AM when the indoor temperature is lowest.)

author: Halcyon
author_rank: Unknown
timestamp: August 11, 2021, 10:40:51 pm
content: Quote from: themadhippy on August 11, 2021, 11:36:27 amNo there isn't. It's an on-demand heater. It stores no water and only lights when you turn on a hot tap.Quote from: andy3055 on August 11, 2021, 07:48:35 pmThanks. He did say it's likely going to be a neutral to ground fault, but as always, the fault is never there when they test it. I'm going to keep a log over the next few days to see if there is any common element here.Quote from: MrMobodies on August 11, 2021, 08:10:42 pmI do have a water pump but I don't use it, plus it's on its own circuit. Physically disconnecting it made no difference last night either.

author: lwatts666
author_rank: Unknown
timestamp: August 12, 2021, 01:21:17 am
content: My parents has a similar problem.Finally found a termite nest behind a power outlet, and a pile of fried termites in the wall cavity. Called the exterminator and then replaced the power point.At least it identified the termite problem before they did any significant damage.Never figured out why it always tripped at night.

author: james_s
author_rank: Super Contributor
timestamp: August 12, 2021, 02:43:33 am
content: I don't know a lot about termites but I would guess they are dormant during some part of the day, either based on sunlight or temperature.I've heard of condensate leaks from air conditioners causing GFCI tripping, it can seem pretty random if it only happens when the AC has been running for a while.

author: Halcyon
author_rank: Unknown
timestamp: August 12, 2021, 03:55:38 am
content: Quote from: james_s on August 12, 2021, 02:43:33 amYeh I thought about that, since it's a ducted system, I got up in the roof and checked. No signs of any water or leaks anywhere. Even if the pipe had been leaking, there are no affected power cables anywhere near it anyway.

author: aargee
author_rank: Frequent Contributor
timestamp: August 12, 2021, 04:26:07 am
content: Our random tripping event turned out to be the heater-to-frame breakdown in the dishwasher pump mechanism. The dishwasher randomly did it a few times, then failed permanently.I'd be thinking vermin as well.

author: Halcyon
author_rank: Unknown
timestamp: August 12, 2021, 05:31:53 am
content: Yeh vermin is something I haven't ruled out yet. However it's suspicious that it has only happens at a particular time of day. I've also gone through the house, inside and out and through the roof and have seen no signs of flying ants, rats, mice or possums. As a precaution I placed some mouse/rat baits down near the entry points where they could possibly get in and in the ceiling and none of them have been touched. No signs of any droppings or similar either. It's also very quiet here so the slightest sound and you'd hear it.I also haven't ruled out moisture in the en suite bathroom. I have a habit of showering with the extractor fan off and the door closed so it does get very steamy and condensatey (if that's a word) in there. I won't be doing that today, so we'll see what happens.

author: Halcyon
author_rank: Unknown
timestamp: August 13, 2021, 10:10:14 am
content: Update:Both yesterday and today I have had no trips. I haven't completely identified the cause yet, but I have taken to placing gaffer tape over the power outlet in the main bathroom to prevent moisture ingress, showering with the extractor fan on and purposely not having a second shower in the afternoon/evening (around the time the issue was occurring).Everything else has remained the same so far.