RCD tripping

Coyote · November 02, 2023, 08:51:21 PM

I am having some issues with the house electrics and I am not sure in what direction to proceed...

On Monday our builder's electrician was here to upgrade the electrics so that we get ECIRE certification. This involved fitting two wired interlinked mains powered smoke detectors and replacing the MCB's for our lighting circuits with RCBO's, the detectors were then connected to lighting circuits as this was easiest to do. Everything seemed OK until Tuesday morning when the RCD for the sockets etc tripped once while using the shower. Reset it and put it down to bad luck. On Wednesday morning it tripped six times in the morning, twice mid shower, and more times afterwards, not much else was in use except fridge, freezer and cable modem. It tripped once again mid shower today. There's four of us in the house so the shower works without tripping most of the time. Until this week the RCD rarely trips, I think the last time was about ten years ago in a hedge trimmer incident.

The builder says its nothing to do with him and the electrician will not return as he did not touch the RCD for the sockets.

I was trained to work and fault find on 100v and 600v circuits but not domestic circuits, so I have some knowledge but not the answer to what's happening. Tempted to take the front cover off the consumer unit to see what the electrician has done, replacing an MCB with a RCBO is straight forward but each RCBO has a Neutral wire that needs to be connected somewhere, could these be in the wrong place? I could get an electrician or a plumber in to check the shower but most of the time the shower works perfectly, and would probably be fault free when tried. The shower unit is permanently powered and activated by a low voltage switch on the shower controller and I would hope the mains input is well isolated.

Anyone had something similar to this?

Dave

geoffc · November 02, 2023, 10:27:58 PM

The neutral wire (blue) of the RCBO connects to the neutral bus bar in the consumer unit the positive input and output connect to the RCBO.
It would appear from what you have said that the RCD is on a completely different circuit, so it would appear that there is an intermittent fault on that circuit. With the RCD the circuit inputs and outputs, both positive and neutral, connect to the RCD.
Either you have an intermittant short in the consumer unit or somewhere in the circuit, have the builders put a nail or screw through the cable?
You can buy a RCD tester, if it were me, already having an RCD tester, I would disconnect the output wires fron the RCD and connect a test lead with a 3 pin socket on it, plug in the RCD tester and test the RCD.

Geoff

ShakyZZR · November 02, 2023, 11:09:58 PM

You say the spark fitted new RCBO's for your lighting circuits but then mention that the RCD trips so I'm guessing that you've already got a split-load CU, is that correct ?

If the spark has wired the RCBO's into an already protected (i.e. one of the split loads of the CU fed by an existing RCD) part of the CU, I would say you need to get him back to sort it as that is completely unnacceptable.

Did you get some paperwork off him re: the pre-testing of the existing lighting ccts before changing from MCB to RCBO protection as you can't just swap them over without testing first as there could be an existing fault on that particular circuit ?

Don't forget that an MCB is only an overcurrent protection device, whereas an RCD (or indeed the "balance monitoring" section of an RCBO checks for an imbalance in the circuit. Basically, if you short the Neutral to CPC (Earth conductor) on an MCB protected cct, nothing will happen but an RCD or an RCBO would trip as it senses the imbalance between the conductors.

I'm also a bit concerned that you describe the Sockets RCD tripping also takes out the Shower, when this should really be on it's own dedicated cct at the CU.

Coyote · November 03, 2023, 12:23:19 PM

The builders finished over a month ago,if they have damaged a cable I think it would have shown up before now.

Yes, there is one RCD for all the sockets etc including the shower which has another RCD located elsewhere, this does not trip.

I was promised paperwork, and have asked again but so far nothing.

ShakyZZR · November 03, 2023, 05:52:54 PM

Quote from: Coyote on November 03, 2023, 12:23:19 PMThe builders finished over a month ago,if they have damaged a cable I think it would have shown up before now.

Not necessarily as if a cable was nicked, it may take a while for any dampness that is present to cause a fault condition serious enough to cause an RCD to trip

Quote from: Coyote on November 03, 2023, 12:23:19 PMYes, there is one RCD for all the sockets etc including the shower which has another RCD located elsewhere, this does not trip.

The "ECIRE" you mention (prolly a typo as it's actually EICR) just stands for an Electrical Installation Condition Report which is just that, a report on the current condition. It may not be up to the current required standards for NEW installations but could still be OK. However, the bit I'm worried about is the fact you say there is an RCD protecting the sockets & shower but there is another one attached to the shower in another position. That is completely wrong and should've been picked up by the spark doing the EICR ! There is no need for more than one RCD to be in one cct and indeed, it can cause nuisance trips, as you are experiencing.

Quote from: Coyote on November 03, 2023, 12:23:19 PMI was promised paperwork, and have asked again but so far nothing.

The current ruling on self-certification by sparks is called Part P of the building regulations (look it up online) but basically it states that unless a spark has his own Part P registration (where he can sign-off on his own work) he either has to be a member of a scheme or get the Local Building Authority (usually the Council) to inspect and commision his work once he is done.

Hopefully, it'll just be an oversight or the spark just had a bad day but I personally would be a bit concerned as to the quality of his work if I was you. Either get him to come back and ask him to explain what/why he has done or get another body to check his work. if you're happy and feel safe doing it, you could always remove the front cover of the CU (only do this if you're comfortable and don't touch anything) and post a good quality picture of the innards.

|There is also a very good site online called diynot dot com where you could ask the questions and I'm sure they'd be able to help.

Hope you get sorted without too much fuss.

Trainfish · November 03, 2023, 10:08:23 PM

I agree with the above and I would never have 2 or more RCDs/RCBOs on the same circuit as nuisance tripping is exactly what it says, a nuisance. I think you said that there's an RCBO rather than an RCD which would give you both overcurrent protection and fault protection. Many people call them both an RCD though. It's also quite unusual to have an RCBO on a lighting circuit, an MCB is usually sufficient but maybe the 18th edition of BS7671 states this, I don't know.
As for the shower being on the same circuit as the ring main, this is not ideal. However, I'm assuming the shower is not an electric shower (usually 8kW+) and is actually a shower pump. The difference here being that an electric shower will heat the water from cold whereas a pump (power shower for example) just pumps hot and cold water from your plumbing system. An electric shower will typically draw 30A or more whereas a shower pump will usually only draw around 2A so you can get away with it 'sharing' the ring main.
I'm not convinced that the work your electrician carried out has had an impact on the ring main and is causing your tripping. Without seeing it and if as it sounds the RCD only trips when the shower is being used then I would guess you have an issue with the shower pump, possibly an internal water leak onto the electrical side of things. If you don't have confidence in your previous electrician then I would recommend using another and if he finds an issue with the original electrician's work then you can pull him up on it.
I'd be interested in hearing the outcome of this anyway. I would offer to take a look myself but there's not much chance you live anywhere near Devizes is there?

Coyote · November 04, 2023, 11:02:44 AM

The elctrician called it an ECIRE which I have googled and got nowhere as he means EICR. I have asked again for some documentation for his work but still have nothing to show.

After five days of tripping I think I know what he has done but not why. Somewhere in the consumer unit he has touched the solar connections, which is why it only trips as the sun rises above our neighbours house every morning, clouds permitting. Later when I am not alone I will look inside the consumer unit and take a few photos.

The shower is a thermostatic type, with the only the pump being electrically powered, and the RCD has tripped when the shower was not in use.

My sister in law lives in Devizes an its a long drive from Orpington and we still have not worked out the best route.

Dave

Trainfish · November 04, 2023, 11:32:43 AM

The electrician is starting to sound 'dodgy' if he can't come up with any documentation whether it's a EICR or even a minor works certificate. You can even download blank forms from the IET website and many other places. I don't know anything about solar systems but what you say regarding he has maybe done something in the consumer unit regarding that sounds feasible. A picture inside would be good especially if you can fit in the circuit schedule. The first thing I would be looking at is whether there are just 2 wires in the 32A ring main RCBO. There's no excuse for there being more in my opinion although it is allowable. Shower may well be fine again from what you say regarding the tripping only when the sun rises so yes, maybe something to do with the solar.

Yes, Orpington to Devizes isn't a simple route and there's not 1 which you would take every time. I often drive to Kent for work but I generally only go as far as the M20 or the A24. To get there I generally go on the A342 then A303, M3, M25 etc, I never go near the M4. It can be a nightmare at the moment getting past the M25/A3 junction though so I have been known to return by coming off the M25 before the A3 junction and head towards Guildford on the A246 then the A31, A331 then back on the M3.

I have a good friend in Devizes whose daughter's partner/husband's family live in Orpington. I don't suppose the surname Mitchell rings any bells does it?

Coyote · November 05, 2023, 11:08:50 AM

Sorry, never met any Mitchells in this end of Orpington.

I did not look inside the consumer unit yesterday, I got distracted by the cricket, I did't want to turn the power off and miss our victory over Australia. It turns out that I should have and would not have been disappointed yet again, then cake baking started which can't be interrupted.

In the photos, it's the main RCD in middle that trips, the RCBO for the solar is immediately to the left. I will try to get some progress with this tomorrow.

Dave

Trainfish · November 05, 2023, 01:13:09 PM

I hope you're ready for a lot of questions here

Firstly, it's good to see you turned the main isolator off before removing the cover. No matter how confident you are this should be done each time as you never know what is behind. Same when putting the cover back on, leave the main isolator off until the cover is secure.

This leads me on to the first check. Make sure the cover screw on the left isn't going into the neutral cable behind it. It looks like it may be close.

Ok so you have a split load board. Without seeing the busbar underneath the MCBs etc I would say that the 30mA RCCB in the centre protects all the circuits to the right of it.
First question has to be, are there 2 cables in the 40A MCB marked shower? Or does the picture just make it look like there are 2? There should be just 1. If there are 2 cables then my first action would be to remove the smaller cable and see what's not working in the house.

Judging by the shower circuit having a 40A MCB it looks like you either had or still have an electric shower rather than a pumped system. Did you say there was another RCBO or MCB nearer to the shower? If so I would personally remove it and replace it with a suitably sized MCB or if the 40A MCB in the consumer unit is suitably sized you could remove the 'local' RCBO/MCB from the circuit completely. The other option if it is a pumped shower would be to downgrade the 40A to something like a 16A. You would then still have the RCCB in the circuit with either 1 or 2 MCBs (depending on whether you remove the 'local' RCBO/MCB) which isn't an issue. Remember, the MCB in the consumer unit is only protecting the cable and not the device on the end of the circuit. This is why we have plugtop fuses etc for household appliances plugged into a ring main which is rated at 32A and not 13A as the plugtops are. Anyway, I digress.

Moving on, it appears that the PV is on the 10A RCBO immediately to the left of the RCCB meaning that the issue, if everything is as it appears, is on 1 of those circuits to the right of the RCCB which eliminates the PV system being on the left of the RCCB. My suspicion goes back to the shower I'm afraid. The other suspect would be a kettle, heater, electric fire, maybe even something in the garage. You would need to use the process of elimination here. When the power trips note what you have plugged in or working at the time and if possible remove something (maybe isolate the garage) and see if it happens again. If so remove something else and so on.

The wiring in that consumer unit is an absolute mess. It has 2 different wiring colour schemes which isn't an issue safety wise although there should be a sticker on the front of the unit to state this. The main reason I mention the wiring colours is because the PV appears to be on the old colour scheme of red/black rather than brown/blue. As red/black was replaced by brown/blue in 2006 for new installations, and I'm assuming the PV system is newer than this, it does seem a little odd. This could indicate to me that an existing circuit was utilised for the PV rather than a new circuit installed. I'm not familiar with PV wiring as I said before but I'm guessing that judging by the fact there are 2 reds in that 10A RCBO it must need 2 or more supplies. Either that or it's feeding something else in addition to the PV. PV is something I could do with knowing a bit more about in general but to be honest as I rapidly approach retirement age I'm not too interested in learning new stuff unless I need to.

Finally, and I maybe should have mentioned this earlier, it may be worth checking, if you're confident to do so, that the neutrals are all terminated in the correct section on the neutral bars at the top. If not you could get nuisance tripping on the RCCB. By that I mean if the neutral from the RCCB is in N2 as it appears to be then all the circuit neutrals from the right hand side of the board should also be in that block which I'm assuming are marked 6 - 10.

I will just add that although the CU is a mess compared to something like this it doesn't look particularly unsafe so no need to panic there. If it were mine I would tidy it up so things are easier to follow etc but you do need to know what you're doing and ideally be qualified to do so. If not it would be worth getting a second, or is it third opinion from a suitably qualified and NICEIC registered electrician and maybe even ask them to do a full test and inspection and tidy up the consumer unit.

I hope some of this helps and I also hope the cake was ok. I only watched the highlights of the cricket as I have a very low pain threshold and couldn't bring myself to watch the whole thing.

Coyote · November 05, 2023, 03:49:41 PM

Live Working, been there many times, somewhere in the garage are my old gloves for it and never felt happy wearing them.

I have tried tucking the neutral cables away from the cover screw, but I don't know where they go when the cover goes back on,they are too long. The left side squashes the cables, the right hand side is fine.

I think there is only one cable in the shower MCB, in the photo it looks like another red cable loops down towards the MCB and goes up again. The label for this MCB is incorrect but should read Shower/Immersion. It was installed for a power shower but now it is just a pumped one, so 16A would be a better size for this one.

I was in bed Saturday morning thinking about getting up, the sun came out and the power went off with the RCD tripping again. Nothing in the house was in apart form fridge, freezer and internet. I turned the solar off last night and this morning the RCD did not trip, the first trouble free morning since the electrician's visit.

I think the RCD trips when the solar starts to feed power to the house, once the sun is fully out everything is ok. The RCBO for the solar has never tripped even though it is a 30mA version, the inverter's manual states it should be 100mA. The solar RCBO has a neutral wire and I think this has been put in the wrong place so that the main RCD is getting a mismatch in current flow in its Live and Neutral coils causing it to trip. So refitting the RCD for the solar would clear the problem.

I don't know why the solar wiring appears to be doubled up, I will check this next time the cover is off. The solar is 11? years old, like the shower work I was not at home when it was done so don't know as much about the cabling as I would like to.

The CU does need a tidy up and it may happen once we have finished with builders, electricians and Building Control.

My wife was baking a gluten free lemon drizzle cake for her art class, it smelt good as the few crumbs I was allowed proved. Cricket - it seems like some of our star players are picked for the names not their current performance (Root, Bairstow) or fitness (Stokes).

Thanks for your replies, your words have been very useful and given me some good pointers.

Dave

Trainfish · November 05, 2023, 07:03:44 PM

You just mentioned an immersion heater. Is it turned on? That would now be my top suspect. Try turning it off. If it has a double pole switch then it should be suitably isolated. If it has only a single pole switch it can still trip the RCBO when turned off. Neutral faults are just about the worst faults to find usually and most faults are down to anything with a heating element as mentioned before, kettle, heaters etc..

I'm glad you found some of what I posted useful. It is of course a lot easier to sort out at the scene as it were though and I'm sure it wouldn't take too long to find. Good luck with it

Coyote · November 05, 2023, 07:51:23 PM

I had forgotten about the immersion heater but I don't think that is the cause although it is closely involved. The heater is not wired as normal but connected to an iBoost unit that only turns the heater on if the solar is making excess electricity that we are not using in the house. So it would not be turning on just after sunrise as the first few watts from the solar go on household items. Today's reading on the iBoost shows that it has used a few kW heating hot water without tripping any RCD so I don't think it is the immersion causing the issues. I have isolated the immersion but left the solar on for the morning to see what happens.

Trainfish · November 05, 2023, 08:16:03 PM

It will be interesting to hear what happens in the morning then. That's part of the elimination process anyway

stevewalker · November 05, 2023, 11:43:17 PM

I'd definitely be checking that every neutral goes to the correct busbar. One going to the wrong one would cause trips.

One thing to look at in the future is getting rid of the RCD completely. I too have a Crabtree (Starbreaker) Consumer Unit and I replaced the busbar with a non-split-load version, removing the RCD and replacing all the MCBs with RCBOs. Before the change, we had random trips (put down to lots of electronics with leaky mains filters and a single RCD covering the whole house. Since the change, we have not had a single trip.