MCBs tripping randomly?

[Lewis Curle]

Hi all,

So I’ve been having a strange fault in my house which has just appeared over the past few days. About a month ago I moved my pc set up into the sun house to make space for my second kid.

Inside the sun house/garage I have a DB that is fed of a 40A type B breaker fed by a 6mm core cable.( it’s not a SWA it’s a wierd cable with loads of little cables as a neutral) but I have insulation resistance tested that feed cable and it’s all good. On the garage DB I have a 32A ring main and a 6a lighting circuit. I have had my pc setup in there for a few weeks now and it’s been totally fine up until a few days ago when the 40A MCB is tripping of at random times. It can go off when I’m there and gaming or off through the day when I’m at work.

The circuits in the garage have all tested out totally fine and the feed cable going to the garage DB has tested out fine as well. But for some reason the 40A MCB in my board keeps tripping off. I have changed the MCB as of yesterday and it has went off again today whilst I was at work. There is nothing on in the sun house when the MCB trips. 40A is huge MCB for a house and I can’t get my head round what is causing it because there isn’t even anything above 10A going through that circuit.

Now this would be fine if it was just this circuit going off. As I could slowly work my way through what is wrong with it. But over the past 4 days as well as my garage MCB tripping I’ve had both upstairs and downstairs rings trip off, and as of today the upstairs lights have also tripped off.

They sometimes trip at the same time as the garage but they have tripped off just by themselves. I have tested all the rings and they appear to have no issues with the cables.

What makes it even more confusing is I have a split RCD DB, not once has the RCDs ever tripped on either side. But I have had the garage MCB trip on the left RCD and lights on the right RCD trip at the same time. This has also happened with the ring mains in the house.

I can’t get my head around how a single circuit on its own like the garage can appear to have an effect on another single circuit that are on separate RCDs.

Could it be an issue with the DB itself? Because as far as I can tell after testing each cable they haven’t got any issues. The MCBs can stay on for hours and just trip off.

Any help into this would be great as I’ve been pulling my hair out for days now.

Thanks, Lewis

 

[marconi]

Lewis Curle: have you been able to investigate this problem further to your last message?

 

[Lewis Curle]

Lewis Curle: have you been able to investigate this problem further to your last message?

Hello mate sorry for being MIA again, I’ve just had my second kid so been very busy with her!

I’ve not had much chance to look into it but what I can say which is new is, the couple of times I’ve had to time to give gaming a go a couple of things have happened.

The first was when the sun house MCB tripped a few other 32A sockets in tripped.
Another time my partner turned on the oven in the kitchen and for a split second everything in the house lost power and came back good again. Nothing tripped in the distribution board but my pc turned off and back on again very quickly.

Seems like an overload but I know for definite that there isn’t anywhere near enough amperage getting used down the sun house circuit. (I measured this with my amp meter and at full usage with my pc, heater and lights all on. It measure out at 13ishAmps). It still looks like having other things on in the house is somehow effecting the sun house circuit. Again I’ve tried just having my pc on a temp ring main but the result is still the same. But the pc worked for a week when I moved it back to the upstairs ring.

I’ve spoke to my electrical distributor and they say it sounds like a loose connection somewhere. But I’ve checked every connection in the distribution board twice over and the connections in the meter box that I can access. I’ve got them coming out next week to check the connections that im legally not allowed to touch.

But so far I’ve still can’t figure out what is happening .

The sun house has continued to trip and what seems like random times for the past 3 weeks to and my pc isn’t even turned on at the plug right now. So yeah still very confused mate!

Thanks for getting back in touch though

 

[marconi]

More and more it seems to me that the fault lies with your electricity supply cabling. The oven switch on event with power outage suggests a poor connection upstream of your main consumer unit. And you have been clear that other mcbs in the house mcb trip occassionally.

I reckon the reason your 40A mcb for the sunhouse trips often is this type of cable has a higher linear capacitance than other types of cables because the N and E are wrapped around the central line conductor which makes a capacitor with large area plates with small separation between them. The surge charging current of this cable is Ic = C x dV/dt which where dV/dt is the rate of change of potential between the 'plates' of the cable capacitance. Thus high C and high dV/dt produces high Ic often of such magnitude to be interpreted by the mcb as a short circuit fault.

This charging current can be even higher than simply C x dV/dt if the cable is charged between L-N say + and - (or - and +)when the power outage happens and it is reconnected to the supply during the part of the mains cycle when L-N is - and + (or + and -) because then the supply emf and capacitor stored potential are added together.

Capacitance of underground cables - https://www.electricaleasy.com/2017/04/capacitance-of-underground-cables.html

Your gaming power supply perhaps stimulates this supply poor connection to fail during high game load because it draws a very peaky current waveform.

 

[brianmoooore]

Another time my partner turned on the oven in the kitchen and for a split second everything in the house lost power and came back good again.

This is the key phrase. If the power went off, and came back on again with nothing being done, then short of there being a local momentary power cut affecting the whole area, it can ONLY be a 'loose connection' of some kind, from, and including, the main switch, back to the branch off of the local supply network.

 

[marconi]

Forgive me for not saying so earlier - congratulations on your new baby daughter! What good news.

 

[Lewis Curle]

This is the key phrase. If the power went off, and came back on again with nothing being done, then short of there being a local momentary power cut affecting the whole area, it can ONLY be a 'loose connection' of some kind, from, and including, the main switch, back to the branch off of the local supply network.

Thank you to both of you for replying! I am going to get the electrical supply people down this week to check the connections that I can’t check. In the meter box that is. I am very confident that there is no loose connection inside my DB.

I will let you know if anything is found.

Thanks!

 

[LastManOnline]

Another question is it even possible for a single circuit such as the garage one, to have an effect on other circuits in the DB.
[/QUOTE]

No.It is,nt.If the other circuits are connected in parallel rather than in series and if the fault in question is an overload.The electrical issues you have described are very unusual and unlike any I personally have ever experienced.
90% of domestic electrical faults will be become known in 90 seconds or less.The other 10% will take a little longer but generally you are leaving the premises within an hour with your callout fee in your pocket.
The one crucial factor that I find could be the solution to this intriguing problem is the presence of a conventionally trained electrician on site. (Though you are clearly very clued in)

 

[Jamie sparky]

This is a conundrum, I have only quickly browsed through the comments. Do you live in a rural area? And do you have a PME supply?

 

[Jamie sparky]

Issues like these will normally have 2 solutions. Either you have multiple faults occurring simultaneously which is unlikely or you have an unusual fault that you don't often encounter. The only possible fault I can imagine is a dodgy neutral on a PME seystem, this will not necessarily trip RCDs nor will it show on consumer side testing

 

[Lewis Curle]

This is a conundrum, I have only quickly browsed through the comments. Do you live in a rural area? And do you have a PME supply?

I live in the outskirts of a city, so not really but yes at the same time I’m pretty sure it’s a TNCS, the earths and neutrals are connected somehow in the DB.

But there are no additional earth points in the house, like a spike for the garage or anything like that.

 

[Jamie sparky]

Just want to confirm some details. The issue occurs with the mcb tripping that feeds a sunhouse with your pc being the main significant load. You also have others circuits trip spontaneously in the dwelling but they are seemingly intermittent and do not occur instantly when any load is present. You have a split rcd consumer unit and the fault can occur on both sides of the DB but do not trip the RCDs

 

[Jamie sparky]

Also would like to congratulate you on your recent arrival and I am also a bit of a PC freak too lol

 

[Lewis Curle]

Just want to confirm some details. The issue occurs with the mcb tripping that feeds a sunhouse with your pc being the main significant load. You also have others circuits trip spontaneously in the dwelling but they are seemingly intermittent and do not occur instantly when any load is present. You have a split rcd consumer unit and the fault can occur on both sides of the DB but do not trip the RCDs

Yeah so long story short. The sun house MCB trips out when I’m on my pc which is now in the sun house. It only trips when things in the house are being used, I can game for hours when my partner isn’t cooking or watching tv (basically using anything in the house). She’s definitely not doing it purpose I want to make that clear as it’s been mentioned

It sometimes trips in 10 minutes and sometimes it takes an hour but as you can imagine as a gamer that’s basically unplayable. It worked fine in the sun house for 2 weeks then it started happening seemed to happen with the rain and bad weather coming in.

I’ve tried basically everything you can think of. Even running a temp ring main through to the sunhouse whilst the sunhouse was totally disconnected. My pc setup alone was plugged in to that temp ring main, but the MCB was still tripping. We’ve talked about this in the forum but the sun house alone isn’t the problem.

It’s not my PC because it works totally fine in the house, it can’t stay in the house because we need the room for baby number 2. Thanks for the congratulations!

We’ve now discovered that the house sometimes loses power for a split second, when heavy loads get fired up like the oven. This has only happened a couple of times though. To my memory it’s only happened when my pc has been on in the sun house. I’ve checked all the connections in the DB and the meter box (that I can legally touch). Found nothing and the fault is still happening. It’s a maddening fault but I’m waiting on the electrical suppliers coming out to check the connections I can’t touch to see if any are loose.

But I’ve had a lot of great people trying to help out in the forum and I’m sure we’ll figure it out eventually. But any advice you can offer also would be welcome!

Also nice setup I’m jealous that you can use it with no issues

 

[Lewis Curle]

Just want to confirm some details. The issue occurs with the mcb tripping that feeds a sunhouse with your pc being the main significant load. You also have others circuits trip spontaneously in the dwelling but they are seemingly intermittent and do not occur instantly when any load is present. You have a split rcd consumer unit and the fault can occur on both sides of the DB but do not trip the RCDs

So other MCBs have tripped but it’s mainly the sun house one. The RCDs have never tripped. MCBs on either RCDs have tripped yes and I’ve tried swapping the sun house one so it’s been on both RCDs. The sun house MCB has tripped when nothing in the sun house has been on. But mainly happens under load

 

[Lewis Curle]

Forgive me for not saying so earlier - congratulations on your new baby daughter! What good news.

So I’ve had chance to get busy on investigating this more.

1. I have been in every connection that is involved with the mains coming into the house. The connection coming out of the 100A fuse has been checked, followed by the meter, then the isolation switch. All of this is in the white cut out on the side of my house. Nothing obvious I got a couple of quarter turns on some but either way the fault happened after checking that.

2. I have fitted a separate RCD one way DB next to my house DB. This is for the sole purpose of the garage being on its own. I double up the mains in the top half of the main isolator in the house DB and used that to feed the new garage DB.

So the garage/sunhouse is a stand alone thing as far as the wiring goes the only thing is has in common with my house is, the cable from the cutout (meter box) to the DB.

I fitted it at around 1pm today and I’ve had my pc on since that time. The 63A RCD main switch has tripped as of about one hour ago. Didn’t notice anything he effected in the house. So this is the first time that an RCD has tripped during the whole of this fault.

I wasn’t gaming in my pc I just left it on watching a YouTube video. We’ve had a busy day in my house with all sorts of appliances being used. Can’t tell when it tripped specifically but it was around the 6-7pm mark.

So it’s ran for 5-6 hours. I didn’t find any loose connections inside the DB, I had to terminate it all again to make this new DB fit. So pretty confident that is no longer the issue.

The only thing I can think of to do now is to run a totally new mains cable from the meter box to my garage which will be Atleast £100 of cable. Just to totally separate it from my house. Would rather not but it’s the only thing I can think of to do now

Hope all of that made sense, I’m still very puzzled and feel like I’m never gonna sort it.

Thanks for reading