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Since a couple of days, the main breaker has been tripping several times a day - without a single easily identifiable cause like, I turn on X device and it trips, or I use this outlet and it trips.

So, how can I debug what the problem is? As mentioned above I've tried isolating to specific items or places but it still trips several times per day since a couple of days. Doesn't seem to be related to load either as it sometimes trips with barely any load at all.

Now that I write this the only constant is the refrigerator, but I don't want to turn it off for a long time to test that.

So, summing up, how would a professional electrician go about finding the problem here?

EDIT: One detail that may be important is that when putting the breaker back up it sometimes creates a visible spark

EDIT: This is the breaker (The one with the orange "Test regularly" button) Breaker

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  • Is this a simple main breaker? Or is this a whole house RCD (Europe)? Commented Aug 13, 2021 at 6:56
  • It's the main breaker for a house (the breaker box has plenty of breakers for different rooms/outlets, and the box has a main that breaks the circuit for the whole house) This breaker is the one tripping. Note the edit though, may be important?
    – user140034
    Commented Aug 13, 2021 at 6:58
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    Trial and error and time. Had one that was a damaged wire in yhe roof - took me a long time to find that. Another was a floorboard nail through a cable - that was well hidden. Good luck searching.
    – Solar Mike
    Commented Aug 13, 2021 at 10:25
  • @ParibusCeteris -- does the breaker that is tripping have a TEST button on it? Commented Aug 13, 2021 at 11:25
  • @ThreePhaseEel yes, and if you press it it trips.
    – user140034
    Commented Aug 13, 2021 at 11:26

3 Answers 3

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TL;DR Ground Fault, not overcurrent

This is an RCD, Residual Current Device. It detects the difference between hot and neutral and trips if more than 30ma. It is not as sensitive as a US GFCI, which trips 4ma - 6ma. It is also a regular circuit breaker tripping at 40A.

An RCD or GFCI is very sensitive. In fact, so sensitive that an RCD has to have a higher trip level than a GFCI simply to avoid nuisance trips from accumulated minor problems, because it protects a whole house instead of one branch circuit.

Note that despite the word "ground", a ground fault does not necessarily involve a "ground wire". In fact, the big problem with a ground fault is that it can involve a human instead of a ground wire. In the US, a GFCI can actually be used to provide protection instead of a ground wire where a ground wire is not available.

The refrigerator may well be the primary source of the problem. In fact, such problems are why many places in the US allow a refrigerator to not be GFCI protected even when most other circuits in the kitchen require GFCI protection. Unfortunately, with a while house RCD troubleshooting is a little more complicated because you can't just move the refrigerator to an unprotected circuit. If the problems happen frequently enough you can try unplugging the refrigerator for a few hours - with a sign on it that nobody should open the door - and see if that resolves the problem. If it does, it may be time for a new refrigerator.

Also keep in mind that ground faults, particularly small ones that add up together to trip an RCD, could be almost anywhere. That includes appliances that are plugged in or hardwired, even if they are turned off, because (a) the power switch doesn't necessarily turn off all power (especially the case with computers, but also any device that has a clock that is on when the rest of the device is off, etc.) and (b) there can be wiring issues in a device between the wall and the power switch. There can also be problems, due to dirt, bugs or water, in the wiring itself (junction boxes, receptacles, etc.) so that even with every device unplugged you could still have an RCD trip.

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  • I doubt it is the refrigerator as it's a less than two years old Miele (fairly okay brand) not even out of warranty yet. Not an old cheap piece of crap. Anyway - what exactly ground fault means? Maybe the outlet where the fridge is is not connected to ground...
    – user140034
    Commented Aug 13, 2021 at 14:38
  • You can use a portable electrical safety box which has a similar breaker. If you are lucky it will show which device is faulty. I say lucky because the main may still break first. Commented Aug 13, 2021 at 14:41
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    You need to take a judgment-free systematic approach to isolating the fault. Miele or not, warranty or not, forget about all that. What you have working in your favor is that it trips several times a day, so you can iterate your experiments at that speed. Disconnect devices at the wall or entire circuits at the breaker, in groups, systematically, to narrow things down. You can unplug the fridge for half a day, just don't keep opening the door. You ought to be able to gradually focus onto the problem.
    – jay613
    Commented Aug 13, 2021 at 17:18
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    If it's a mouse or nail damaged wire in the walls, you'll be able to focus onto the circuit but still have the difficulty of finding the physical damage. At that point yo have to start opening outlets and sockets and isolating segments of wire. You may want an electrician to do that if you don't have the experience.
    – jay613
    Commented Aug 13, 2021 at 17:19
  • Note that this device may not have an overcurrent trip (RCCB, not RCBO) Commented Aug 13, 2021 at 22:49
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It's an RCD trip, due to small amounts of current leaking from hot to ground, or neutral to ground. These are the kinds of leaks that can shock and kill people. This is either a faulty appliance, or a wiring problem.

Divide and conquer

You're going to have to unhook things until the problem stops happening.

You start with all plug-in appliances. You unhook half your appliances, and wait as long as it takes for 3 trips typically.

If unplugging half the appliances solves the problem, then you know the problem lies within the appliances you did unplug. Otherwise, plug those back in and unplug the other half of your appliances. If the problem stops happening in either case, then you know which half of your appliances is the problem.

Now, you divide that half of the appliances in half again, and plug in those appliances. If the trips return, then that 1/4 of your appliances contains the problem. Divide that 1/4 again until you have narrowed it to 1 appliance.

If the problem remains with all appliances pulled, then the problem is either in built-in loads, or in the wiring. This is going to be harder. It is not enough to turn off the circuit breaker. You must also disconnect the neutral wire for the circuit or part of the circuit you are testing. But other than that, it is more "divide and conquer".

I doubt it is the refrigerator as it's a less than two years old Miele (fairly okay brand) not even out of warranty yet.

Unfortunately, that doesn't buy you anything. We have reports of brand new refrigerators tripping GFCIs (USA RCDs).

You can try putting a quality surge suppressor on the refrigerator.

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  • Thanks! About the fridge thing - it's just that I think that there are more likely culprits than a new decent fridge, not that it cannot possibly be it.
    – user140034
    Commented Aug 14, 2021 at 2:11
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The spark means there is a load applied. Turn off all bigger appliances before turning breaker on - they don't like being used as switches and will deteriorate.

The breakers have two modes of tripping - overload and thermal.

The first one is breaker simply tripping at short circuit or when you exceed its nominal capacity several times, like when plugging in couple heaters at once.

The second mode works on heat buildup - if you draw max current for long period, breaker heats up and shuts down. This has unusual consequence that breaker will trip much 'faster' than usual when its preheated - normally you can plug that big microwave for 3 mins and all is ok, but now it trips every time. You may be hitting the thermal limit when something is turned on for long time then you add another thing.

Go to your meter and check how much current flows. [I assume the meter is before the main breaker, as is usual]
The meter will have a label saying "this many turns of wheel" or "this many blinks per Kwh". Measure it for minute or two (use timer), then count how much electricity you used in a minute. (Or just turn on electric kettle and compare how fast it turns when its on VS off). You can derive amperage from that. Compare the value to value of your main breaker. If its very small, it might be faulty breaker. If its large, then you have some unidentified load drawing a lot of power. Too many appliances? Bad neighbour/tenant stealing electricity? Arcing wire?
An electrician visit may be necessary - main breaker is not something you can usually replace safely yourself.

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  • Heat is an interesting concept! Trips have started on the heat wave we're in... So I might just keep the box cooler, pointing a fan at it or something...
    – user140034
    Commented Aug 13, 2021 at 10:39
  • Regular air heat is not within operating range of breakers - people will start to trip before breakers do. Check what is stressing the breakers - heat signifies a load on them.
    – Thomas
    Commented Aug 13, 2021 at 11:16
  • There must be some load, but starting from 40ºC is different than starting from 20ºC - no?
    – user140034
    Commented Aug 13, 2021 at 11:22
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    Higher ambient temperature will make the thermal limit be reached faster, but it only highlights that there is some overload issue. Cooling the fuse box will not solve the issue. Wires in walls will still heat up and could start a fire if the issue persist. Check the meter to see how much electricity is used - if there is an issue with "power leak" it will save you a huge power bill.
    – Thomas
    Commented Aug 13, 2021 at 11:28
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    This answer has a fatal flaw: it overlooks the importance of the "Test" button. Commented Aug 13, 2021 at 17:03

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