MCBs tripping randomly?

[timhoward]

Is there anything that you use at same time as your PC that has stayed plugged in throughout? Monitor(s), Speakers, Printer, Fan, desk light.
Had you not already tried a completely different cable I'd have said the most likely cause was a small L-N fault with the split-con cable that tips the balance when under greater load. (It's very difficult to simultaneously IR test every single N conductor and every single CPC conductor, though you may have tested with clips when they are terminated.)

I don't suppose you want to add a clamp meter to your ever growing tool kit do you? They start at around £30 (screwfix)
It would be very interesting to see the reading of the outgoing live when everything is ostensibly "off" in the sun house.
And also the reading when your PC is fired up and running.

 

[Lewis Curle]

Is there anything that you use at same time as your PC that has stayed plugged in throughout? Monitor(s), Speakers, Printer, Fan, desk light.
Had you not already tried a completely different cable I'd have said the most likely cause was a small L-N fault with the split-con cable that tips the balance when under greater load. (It's very difficult to simultaneously IR test every single N conductor and every single CPC conductor, though you may have tested with clips when they are terminated.)

I don't suppose you want to add a clamp meter to your ever growing tool kit do you? They start at around £30 (screwfix)
It would be very interesting to see the reading of the outgoing live when everything is ostensibly "off" in the sun house.
And also the reading when your PC is fired up and running.

So I’ve tried everything plugged in and off and there’s seems to be nothing in particular causing it to happen, it just seems when there’s current at all being drawn down the circuit it can cause it to happen.

I think I have an amp clamp meter already if this is what you are referring to? I will do the test tommorow sir and come back with results! Thanks for your time

 

[timhoward]

I think I have an amp clamp meter already if this is what you are referring to? I will do the test tommorow sir and come back with results! Thanks for your time

Yes, that's what I meant. Obviously take great care when doing this.

 

[brianmoooore]

Also I gamed with no issues for about 3 hours when my partner was out of the house .........

I’m very confident she isn’t turning it off just to make that clear!

Are you absolutely certain of the last statement? If it were my partner disappearing for hours on end to chase pixels around a monitor screen, then it would be highly likely that is the cause.

 

[marconi]

So I’ve tried everything plugged in and off and there’s seems to be nothing in particular causing it to happen, it just seems when there’s current at all being drawn down the circuit it can cause it to happen.

I think I have an amp clamp meter already if this is what you are referring to? I will do the test tommorow sir and come back with results! Thanks for your time

Thank you for swapping the sub main cable which was very helpful.

Are you using those surge suppressor socket strips and if so have they been left plugged in and switched on but with nothing plugged into them?

How long is the cable run in spilt concentric between house db and sunhouse db? I am wondering if there is a cable charging effect which may be tripping the 40A mcb due to voltage disturbances up stream within your house or even external to it. If this was the case there would not need to be anything connected and powered up for the 40A to trip from this cause. But it would be exacerbated by the current waveform of your IT power supply. And also items turning on and off in the home.

As an experiment, please swap the house 40A B (trips on 3 to 5 x 40 ) curve for a same make 40A C curve mcb (trips on 5 to10 x 40 ).

 

[Lewis Curle]

Are you absolutely certain of the last statement? If it were my partner disappearing for hours on end to chase pixels around a monitor screen, then it would be highly likely that is the cause.

Yes I’m quite certain she isn’t turning it off intentionally

 

[marconi]

I have been studying the images of your home consumer unit. It seems the top left securing screw is missing. Has it fallen out and lodged behind the din rail and causing mischief or damage to busbars/cables there which might explain your problem?

I also wonder if the ends of securing screws (the ones present now and also those in place in earlier times) have damaged cables behind the plaster board. Perhaps there are fault(s) hidden out of sight here.

One would have to be very careful investigating because the split concentric is live even with the main switch off and it may be damaged and unsafe.

 

[Lewis Curle]

I have been studying the images of your home consumer unit. It seems the top left securing screw is missing. Has it fallen out and lodged behind the din rail and causing mischief or damage to busbars/cables there which might explain your problem?

I also wonder if the ends of securing screws (the ones present now and also those in place in earlier times) have damaged cables behind the plaster board. Perhaps there are fault(s) hidden out of sight here.

One would have to be very careful investigating because the split concentric is live even with the main switch off and it may be damaged and unsafe.

Hello mate sorry for the late reply, so in regards to the cable that is feeding the garage. In my mind I have already ruled that out since I ran the temporary cable to test. But I didn’t notice the lose holding screw in the board and will investigate. I will be careful so don’t worry!

I have also picked up a 32A type C MCB to swap out and will do as you’ve said in the other comment! I don’t think I’m going to have the time to do it tonight work has been manic. But I will tommorow and will get back to you with results.

As always thanks a lot for your time!

 

[timhoward]

The main reason I was advocating a clamp meter test is that knowing whether the B40 breaker is hovering 'on the brink' all the time is a key clue.
In the absence of this, switching everything else off and watching the electricity meter for a few minutes could be equally helpful!
Swapping to a B32 may also provide a clue.

I can't see how this isn't either
a) A permanent L-N fault that the PC occasionally pushes over the edge
b) an intermittent L-N fault caused by thermostat / timer / sensor or at a stretch the weather conditions.

If you could borrow a small UPS for your PC then it would rule it out as the inverter is essentially an isolating transformer. Or short term try running your PC via a long extension lead from e.g. the cooker switch socket plate and see what trips then.

 

[marconi]

The OP and I clarified a few points PM in order not to repeat much of what was reported in the open forum. Next the OP is going to check sunhouse main switch by disconnecting the N in and N out wires of the main switch and joining them together so that only the line passes through the main switch and then energise sunhouse db via House B40A.

 

[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

 

[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. Nothing tripped in the distribution board but my pc turned off and back on again very quickly.

How certain are you that this happened?

 

[Lewis Curle]

How certain are you that this happened?

It 100% happened! I was in the kitchen when it happened

 

[brianmoooore]

In that case, there was either a coincidental short power cut, affecting your local area, or there is a poor connection in your electricity supply between where it connects to the trunk main and the meter in your house.

 

[Lewis Curle]

In that case, there was either a coincidental short power cut, affecting your local area, or there is a poor connection in your electricity supply between where it connects to the trunk main and the meter in your house.

Trunk main?

 

[brianmoooore]

The main underground cable along the road, or the pole outside where other house supplies branch off, if overhead wires.

 

[yorkieone]

When you say passed an IR test do you mean they had a perfect >999megohm or a just scraped through at 1megohm?



A 40A MCB and a 16A MCB will not discriminate on a fault, it is pretty much pot luck which one will trip first.

1 meg ohm at 500v is ok we would like infinity but it's not an insulation fault

 

[Lewis Curle]

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

Long time no speak everyone, so after a busy few months with the new baby I’m back to trying to figure this fault out. I’ve not been standing idle, I have tried multiple things to try and figure out this bizarre issue.

Short story of it all is I have changed the whole consumer unit in my house for a brand new Wylex one. It’s a split RCD board. First thing I did after changing it was of course test the thing. The issue is still exactly the same after about half an hour of being in the sun house gaming away the sun house MCB tripped along with the upstairs ring and the smoke alarms. Smoke alarms have never tripped before but the upstairs ring has. This was the only time since the new board that those other MCBs have tripped.

So naturally I started to break down the sun house in stages again, I disconnected everything out of the garage DB and the MCB still tripped sometime when I was at work the next day. So i then disconnected the cable feeding that garage DB and taped the ends up and put them safely out of the way of anything. The MCB still tripped. So then I disconnected the the cable at the house db end. And some how the 40A MCB with nothing in it has tripped three times in the past three days. So the sun house has nothing to do with this strange fault in my eyes.

Now I can’t workout how that MCB is still tripping with nothing connected into the thing. The only thing that hasn’t been changed now is the cable that is feeding my DB from the meter box. Nothing has showed up on testing that cable, it has been properly tested and all the results came back perfectly. So now I don’t really have a clue on what to try, other than changing that cable which would be a nightmare to change.

As an electrician I can’t make any sense of it.

I’ve has the grid people out and they have checked the cable into my house and inside the meter box and found nothing wrong.

Now thinking back to the times that it trips and the times that it doesn’t, things inside the house are being used. It doesn’t seem to matter what is being used but it trips a lot more often when my partner is cooking or watching tv downstairs.

I’ve not managed to keep it on for more than an hour when she is kicking about in the house using things. I also would like to say that it is not being intentionally turned off, someone asked that once and I just want to make it clear now!

So thanks for reading, I will attach some photos of the DB and the meter box.

Lewis

 

[brianmoooore]

What is tripping? MCB or RCD?
It's a pity you didn't fit a RCBO board.

 

[Lewis Curle]

I can’t upload the photos they are to big

 

[Lewis Curle]

What is tripping? MCB or RCD?
It's a pity you didn't fit a RCBO board.

The 40A MCB that was feeding the sun house is the main on that’s tripping. Although it’s tripping without the cable in it right now.

 

[DPG]

The 40A MCB that was feeding the sun house is the main on that’s tripping. Although it’s tripping without the cable in it right now.

The 40A MCB is tripping without anything connected to it??

 

[Lewis Curle]

The 40A MCB is tripping without anything connected to it??

Yeah consistently for the past three days

 

[DPG]

Yeah consistently for the past three days

Literally no cable in the output terminal?

 

[Lewis Curle]

Literally no cable in the output terminal?

Literally it’s connected to the busbar and they is nothing coming out of the top side. It’s tripped three times in the past three days. I can’t make any sense of it. Bear in mind it’s a brand new MCB as well.

 

[DPG]

Literally it’s connected to the busbar and they is nothing coming out of the top side. It’s tripped three times in the past three days. I can’t make any sense of it. Bear in mind it’s a brand new MCB as well.

Could you post a photo of the consumer unit with the front off

 

[nicebutdim]

The statistical probability of both old and new MCBs exhibiting the same inexplicable fault isn't worth considering, so there's either a rational explanation, human intervention or this thread is destined to enter rather exclusive territory.

 

[Lewis Curle]

Could you post a photo of the consumer unit with the front off

All the photos I’ve took are too big to upload to this site, not sure how else to to show you.

 

[DPG]

All the photos I’ve took are too big to upload to this site, not sure how else to to show you.

Try taking a screenshot of the photos and also crop them a bit if there's any excess around the edges.

 

[Lewis Curle]

The statistical probability of both old and new MCBs exhibiting the same inexplicable fault isn't worth considering, so there's either a rational explanation, human intervention or this thread is destined to enter rather exclusive territory.

Try taking a screenshot of the photos and also crop them a bit if there's any excess around the edges.

 

[DPG]

My money is on human intervention rather than anything electrical.

 

[brianmoooore]

Haven't looked inside of one for a while, but I take it electronics hasn't found its way into MCBs yet, making them possibly vulnerable to so called smart meters.

 

[Lewis Curle]

My money is on human intervention rather than anything electrical.

Haven't looked inside of one for a while, but I take it electronics hasn't found its way into MCBs yet, making them possibly vulnerable to so called smart meters.

We do have a smart meter plugged in, in the kitchen which is the downstairs ring. I’ve had that unplugged though multiple times when trying different things.

There is only me and my partner in the house and neither of us are doing it in purpose.

 

[brianmoooore]

The mechanism inside any MCB that I've dismantled to date is fairly simple, and, if the MCB is in working order, there is no possible way it can be 'tripped', other than by doing what it's supposed to (which it's not, if no outgoing cable is connected), or perhaps by a mechanical shock, such as hitting the side of the fuse box with a hammer.

 

[nicebutdim]

Any electrical explanation is far beyond my comprehension, but I desperately want to see this thread resolved - especially now the same fault has manifested itself in the same breaker in a brand new board and with no load connected.

 

[James]

Just to confirm.

the original summer house was experiencing random trips
it was fed from a normal mcb

the board has been changed and the same thing is happening with the new equipment

the outgoing live cable has been removed from the circuit breaker and the breaker still trips at random times.

if all the above is correct, i would be looking for a mechanical reason for tripping as mentioned above by @DPG

I would be considering a covert ip camera watching the board with the cover off and seeing what is going on.

edit,
A video of a breaker tripping on its own with no outgoing cable attached would really amaze me.
if that happens, i would be recommending posting on a forum that follows ley lines, ghosts, spirits, extra-terrestrials, EMF and grounding, etc.