Circuit keeps tripping, how do we isolate the issue?

springdove

Hi all. I've had this issue anew over the last three months. On 3-4 occasions now, the Hager RCD Controlled Circuit 282U (which also has the testing button) has tripped randomly, even when not a lot of electricity is being consumed actively.

On previous occasions, we were able to just switch it back on by pushing it back up, but yesterday night, it just wouldn't go up, and kept tripping with the yellow earth fault indicator coming on.

I isolated the issue to the ground floor sockets MTN 132 B32 circuit breaker/switch. I proceeded to switch everything off (as in any devices which are connected to the ground floor sockets) and yet this wouldn't fix the issue. I removed plugs from sockets for most things, the only things still connected via the plug were the dishwasher, frig-freezer and washing machine, (whose plugs I can't reach - yet their switches were off including the fuse switch). I gave up, thinking I just have to get an electrician to come out and check.

Today morning, some 7 hours after this incident, I was able to simply push it up and everything is back to being normal.

Something's clearly wrong though, as we didn't have this issue before and clearly it's now happened on 3-4 occasions, but how do I know what the issue is - is it a problem with the Hager RCD or circuit breakers, or is it a problem with some appliance? If it's the latter, why does switching everything off still not solve the problem?

My plan is to get an electrician to come out, but I just thought I'd post it here in case people have any ideas. Thanks so much for any suggestions, advice or help!

BarelySentientAI

springdove said:

On 3-4 occasions now, the Hager RCD Controlled Circuit 282U (which also has the testing button) has tripped randomly, even when not a lot of electricity is being consumed actively.

On previous occasions, we were able to just switch it back on by pushing it back up, but yesterday night, it just wouldn't go up, and kept tripping with the yellow earth fault indicator coming on.

Protective devices don't trip randomly.  They trip when they detect whatever they're supposed to be protecting against.  An RCD doesn't care about how much electricity you are using, it's not an overload protection device.  It looks for 'leakage' to earth.

springdove said:

I isolated the issue to the ground floor sockets MTN 132 B32 circuit breaker/switch. 

So is it a circuit breaker (MCB) or is it an RCD?  Or do you mean that the RCD that was protecting many circuits was tripping, but you've discovered that it was on the circuit protected by this MCB?

springdove said:

Something's clearly wrong though, as we didn't have this issue before and clearly it's now happened on 3-4 occasions, but how do I know what the issue is - is it a problem with the Hager RCD or circuit breakers, or is it a problem with some appliance? If it's the latter, why does switching everything off still not solve the problem?

Or the problem is somewhere in the wiring, which is live no matter what you do with socket switches.  If I understand the symptoms correctly, which is that the RCD is tripping but only when the sockets circuit is live through the MCB, then it isn't a fault on the RCD (because that wouldn't care which circuits are live) or the MCB (because that doesn't have a neutral or earth connection and can't 'leak').  If you've proved that it isn't any of the appliances, then its likely in the circuit itself.

However, this does raise an interesting point which we have discussed at the office several times.  How many times is it legitimate for a layperson to simply push the switch back on?  As you said, you flipped the switch and it stayed on, so everything must have been alright.  Having dealt with many house fires where there was an electrical fault or overload but the occupant just pushed the switch back on over and over again until their walls burst into flames, this misconception of "I was able to simply push it up and everything is back to being normal" is a point of debate about when it turns into negligence.

Something's making the device trip, it's just a question of what.  You've done the right thing by trying without the appliances, but if that hasn't found it then I think an electrician is the right call.

ThisIsWeird

Hi Springdove.

Chances are, unless it's a really obvious cause (eg, our air fryer was once pushed back close to the power socket, and the socket ended up dripping with the resulting cond - 'pop'!), or you do manage to isolate it by removing all the appliances and manage a few days of no trip, before then replugging them one by one, it's unlikely you will find the culprit.

It's also very possible that the issue isn't on the circuit that makes the RCD trip when you turn that MCB back on... RCD's are sensitive items, and respond to either a leak of current to 'earth', or an imbalance of current betwixt L and N (which amounts to pretty much the same thing). The thing is, the triggering current is tiny at around 35mA. And, most circuits and appliances will 'leak' to some degree - a couple of mA here, a few there. It all builds up, and can get quite close to 30mA with no real issue - and then there's a voltage spike, or a bit of steam, or a failing element in a W/M or oven, something that brings it over the triggering point, even briefly - and 'pop'.

And it might not be on the circuit you last turned back on when it went 'pop' again - the 'main' leak could have been on another circuit, one you turned back on earlier with no issue, and is now happily leaking 20+mA with no ill-effect, and then you turn back on a relatively 'good' circuit which pushes it over t'top!

You can often only point to a miscreant circuit as the cause if only that circuit is turned back 'on' and it makes the RCD 'pop'.

In general, tho', the most likely culprits will be in kitchens, and outdoors - lights, garage supplies, power to t'shed', fountain...

So, I think all you can do is to physically check all the sockets and visible cabling.

Keep_pedalling

You do need to unplug those two devices you can’t reach. Switching off only isolates the live wire so a faulty device can still cause an issue. 

ThisIsWeird

Most likely, the switches will be double-pole. But, yes, if you are trying to investigate the cause, then fully unplugging is the way to go.

Springdove - has any appliance been working less well recently?

springdove

Re this question:  "So is it a circuit breaker (MCB) or is it an RCD?  Or do you mean that the RCD that was protecting many circuits was tripping, but you've discovered that it was on the circuit protected by this MCB?"

So, bearing in mind I am indeed a layperson, I think the RCD is protecting all the MCBs to the left of it - but, when I keep one of the MCBs switched off, leaving the others on, and try to reset the RCD, it works, suggesting that the issue is with this particular MCB. 

Let me add a photo to help explain. 

So, when the trip happens, it's on the RCD in the middle.  If I try to reset the RCD right away, then it wouldn't let me and it keeps tripping back instantaneously.  If I then proceed to switch off the ground floor sockets switch (which is MTN132 B32 - and what I think is an MCB), and then reset the RCD, then the RCD doesn't trip again. 

The following morning, so after a few hours, I am able to safely switch on the ground floor sockets MCB without tripping the RCD. 

I've had this issue as I said, 2-3 times before with days/weeks in between, and now, it's happened on two successive nights.  



When you say "then its likely in the circuit itself" - what exactly does this mean and what sort of remedial work might be needed by the electrician, just for my awareness?

In case I hadn't been clear - on all occasions, nothing actively done by us caused the trip, as I see it.  E.g. it wasn't that we switched something on, and at that immediate moment, this tripped.  It just happened day before at 1 am, and yesterday around 12 30 am.  It's happening at night, and so I wonder if it's to do with the temperature or moisture in the air. 

No appliance has been working less well recently. 

There isn't anything switched on in the garage, which in any case, I think, is connected to the right hand RCB which isn't tripping.  The one that says solar is actually connected to our air conditioner (an installation a few years ago), but this wasn't even switched on when these trips were happening.  Admittedly, the power cabling for the air conditioning is outdoors and it has a plug socket outdoors as well - and these have power switched on, even if the air conditioner itself isn't being operated.  

Lastly - thank you all so much for your responses, I really do appreciate it.  I will get an electrician, but I do wonder what the underlying issue is, and how they'll fix it - especially, if they turn up during the day, by when it's possible to reset the MCB and RCD without issue.  
 

gm0

If it is a pooled RCD there are other possibilities

It is not uncommon for a "pooled RCD" - a single leakage trip which covers a series of circuits to trip. 
As unsurprsingly it "adds up" the leakage current found on each of them.  And if it sees the rated mA - ping
You are not allowed a higher threshold one.

And leakage current can change over time because of a combination of:

- Aging insulation in compressor windings - motors, freezer compressors, wine fridges etc. CH pump.
- The voltage arriving at the house varying within or outside prescribed limits or transients
- An actual aging or disturbed wiring issue on one of the circuits. 

This can be investigated by testing the outlets on the suspect circuit properly.  As would be done with a new CU installation.

We had lots of this nonsense with a pooled RCD of 90s vintage.  And once replaced with RCBO modules which don't add up the leakage and assess it per circuit.  The leakage per circuit is below the threshold.  And voila.  No more trips.  Nothing is measuring "total leakage" across circuits anymore.  Yet leakage current protection is still in place for safety.

It was - I believe - fridge/freezers and the supply voltage variation in our case.  As it occurred several times when the house was electrically fairly quiet.  Holiday. Kids away. Most things off.  Local area voltage may have been up if the general load was down in warm weather and holiday season.

We replaced the CU with a current spec one with a surge protector SPD. 
And individual circuit protection. RCBO to current regs.  Pooled RCD gone to the dustbin (with the old CU and MCB).

Eldi_Dos

Any signs of rodents in the area?

BarelySentientAI

springdove said:

Let me add a photo to help explain. 

So, when the trip happens, it's on the RCD in the middle.  If I try to reset the RCD right away, then it wouldn't let me and it keeps tripping back instantaneously.  If I then proceed to switch off the ground floor sockets switch (which is MTN132 B32 - and what I think is an MCB), and then reset the RCD, then the RCD doesn't trip again. 



 

Perfect, thanks.

Yes, you are right.  That's an RCD in the middle that protects against leakage on everything connected to its left, and then the others are MCBs which trip when there is overloading on a particular wire.

As gm0 and TiW mention, the RCD is adding up all the leakage on all those things and so it might not actually be something in the ground floor sockets that is making it go, or one specific fault at all - it could just be lots of little none-problems adding up overnight (which is also often when strange things happen to the supply to the house as well, so that could be contributing).

Your electrician should be able to measure what's going on, even if it isn't reaching the level needed to trip the RCD when they are there, and rule out obvious problems like a loose wire in one of the sockets or a grossly defective appliance - giving you the confidence to continue with the "turn it back on in the morning" approach knowing it is safe.

A good long term fix would be RCBOs (these do the job of an RCD and an MCB in one switch - and fit in the space of an MCB) - then you don't have the adding up thing going on, and if one trips then it doesn't turn any of the other switches off.

ThisIsWeird

springdove said:

So, bearing in mind I am indeed a layperson, I think the RCD is protecting all the MCBs to the left of it - but, when I keep one of the MCBs switched off, leaving the others on, and try to reset the RCD, it works, suggesting that the issue is with this particular MCB. 
So, when the trip happens, it's on the RCD in the middle.  If I try to reset the RCD right away, then it wouldn't let me and it keeps tripping back instantaneously.  If I then proceed to switch off the ground floor sockets switch (which is MTN132 B32 - and what I think is an MCB), and then reset the RCD, then the RCD doesn't trip again. 
The following morning, so after a few hours, I am able to safely switch on the ground floor sockets MCB without tripping the RCD. 
I've had this issue as I said, 2-3 times before with days/weeks in between, and now, it's happened on two successive nights.  


In case I hadn't been clear - on all occasions, nothing actively done by us caused the trip, as I see it.  E.g. it wasn't that we switched something on, and at that immediate moment, this tripped.  It just happened day before at 1 am, and yesterday around 12 30 am.  It's happening at night, and so I wonder if it's to do with the temperature or moisture in the air.

Thanks for the good info. And you have a good handle on what's going on.

The two 'big' switches with the blue test buttons are the main switches for each bank of MCBs to their respective lefts, and also provide the RCD protection. You can see they have 0.03A printed on them, and this is the 30mA max of leakage they'll allow before tripping.

Then the two groups of 6 switches are the MCBs as you say, and these do a different task - they limit how much each current each circuit can safely draw before tripping. If one of these babies trip, then that usually tells you that you have a short circuit, or have plugged in too many electric heaters at the same time. That is pretty serious, and usually very obvious.

The fact that turning off the 'downstairs sockets' MCB allows the RCD to be reset might mean it's summat on that circuit, but not necessarily so. As said above, all circuits will 'leak' to some extent, and it's when that adds up to 30mA that the RCD trips. So, it's possible that the 'downstairs sockets' is only leaking, say, 5mA, but all the others are also leaking that amount - so 30mA total! Most likely, of course, some circuits will leak a lot less, and differing amounts.

One way to possibly check is to turn off all the MCBs, and then turn only the 'd-s' one back on. This will likely be a bit of a pain, but if the tripping always happens in the early hours, then it might not matter if the lights aren't available when you go to bed? Just turn them back on in the morn.

So, if you can, try all the MCBs on that left bank off when you go to bed, but only 'd-s' on. If you 'must' have another one on overnight - say one of the lighting circuits - then by all means put that one on too. The idea is to properly trial each MCB circuit on its own if possible.

If you have a night owl in the house, and the tripping always happens at 12-1.30am, then that person could turn them all - except the d-s - off after everyone's gone to bed, and then back on at near 2am before they, too, retire?

Obviously the timing is interesting... Obvious Qs - does a 'time switch' operate anything in your house? Air-con? Cheap-rate overnight electricity? Outside security lights? An electric blanket on a timer? (Don't laugh - mine is... :-(  )

If no tripping with d-s, try each MCB in turn. Then pairs of MCBs!

I had 'nuisance' tripping a couple of years ago. I then tried isolating the lighting circuit of our new extension - bingo! Tripping stopped! Called out the installing sparky, he checked it - nothing. And, of course, the nuisance stopped. He told me another house on our road had similar issues, and he could only put it down to voltage spikes sending the RCD over.

gm0

Exactly - the version of part P that pooled RCD comes from was a "cost engineering" as priority rather than "operational resilience" as a priority but at higher cost (both achieving the desired protection and the overrriding electrocution "safety goal"). 

It should have been directive towards per circuit protection.  As it now is.  You can understand why they did it. But it has caused a load of somewhat hard to diagnose and intermittent issues on a minority of installations modern enough to have RCD at all.  But before the pooling idea was dropped.