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

 

[domsta72]

A few questions.
Did you not carry out a full eicr before the board change?
All new colour cables in your photo - a full rewire at some stage, extended circuits or a newish property?
Knowing you have had on going issues, you chose to fit a dual rcd board rather than an rcbo board (and no spd).

 

[marconi]

I am minded - not yet decided since Carlise is half a day's travel each way - to take a look myself so intrigued am I with this problem.

My suspicions have turned to the smart meter. it contains a contactor which isolates the incoming mains in the event of tampering, end of credit, remote supplied command or loss of incoming mains power. The working hypothesis is that there are very brief complete interruptions in mains power to the output terminals of this smart meter caused by some sort of fault associated with this relay or its control including the meter enclosures anti-tamper circuitry. When there is a a very brief interruption in 240Vac when some non-trivial current is being supplied as would be the case when you and /or your wife are using electrical equipment or indeed when fridges and freezers start or run - then the transient currents which flow briefly after power returns to normal causes very high but short duration pulses of magnetic flux in the short circuit solenoid of the mcbs. These pulses of high current high magnetic flux are interpreted by those circuit breakers passing current as short circuits and thus they trip. Oddly but not physically impossible the sunhouse mcb trips even when it is only connected to the busbar but nothing to its output because the high pulse of magnetic flux(es) from adjacent mcbs link its own short circuit solenoid causing it to trip.

These events are initiated and noticeable only when non-trivial currents are flowing thus during gaming, cooking and the use of high power white appliances.

It is still not certain even though the dno have been and tested(? ) that there is no external fault with the distribution network your home connects to noting it is a PME supply. If it was a street long problem others would be complaining - and they are not - so if there was a supply defect then more probably it would be in the feed to your home. Is your street fed by overhead lines?

Would you please load up the ring circuits and your sunhouse too (so reconnect the fed to it to the B40A mcb) and then take a rolling pin or hammer and tap the smart meter in a number of places a number of times. Obviously don't beat the living daylights out of it as much as most of us would quire understandably want to at 50p a kWh!

After this, please take some small plastic clear freezer bags and aluminium foil. Using an mcb as a template cut out two pieces of ally foil shaped to both sides of the mcb. Place these each in a small plastic freezer bag. Interposed these insulated ally sheets between the sides of the mcbs which usually trip. Wait and see what transpires. Obviously take great care that the ally is inside the plastic and does not touch the busbar. No shame if you think this is too risky for you to do. You really do have to be very careful. I only suggest it because you are a qualified electrician. You are making a Faraday shield. See

Faraday cage - Wikipedia - https://en.wikipedia.org/wiki/Faraday_cage

Also wiggle the meter tails to see if their movement causes the trip.

I recall a smart problem in Birmingham when its radio transmissions interfered with the electronics of the rcd causing it to trip - but your rcd does not trip so we will keep that on the back burner for now.

Is the meter cupboard metal or plastic including the door? Is the mobile phone signal strong where you live? How old is the smart meter in the cabinet?

 

[mainline]

I am minded - not yet decided since Carlise is half a day's travel each way - to take a look myself so intrigued am I with this problem.

My suspicions have turned to the smart meter. it contains a contactor which isolates the incoming mains in the event of tampering, end of credit, remote supplied command or loss of incoming mains power. The working hypothesis is that there are very brief complete interruptions in mains power to the output terminals of this smart meter caused by some sort of fault associated with this relay or its control including the meter enclosures anti-tamper circuitry. When there is a a very brief interruption in 240Vac when some non-trivial current is being supplied as would be the case when you and /or your wife are using electrical equipment or indeed when fridges and freezers start or run - then the transient currents which flow briefly after power returns to normal causes very high but short duration pulses of magnetic flux in the short circuit solenoid of the mcbs. These pulses of high current high magnetic flux are interpreted by those circuit breakers passing current as short circuits and thus they trip. Oddly but not physically impossible the sunhouse mcb trips even when it is only connected to the busbar but nothing to its output because the high pulse of magnetic flux(es) from adjacent mcbs link its own short circuit solenoid causing it to trip.

These events are initiated and noticeable only when non-trivial currents are flowing thus during gaming, cooking and the use of high power white appliances.

It is still not certain even though the dno have been and tested(? ) that there is no external fault with the distribution network your home connects to noting it is a PME supply. If it was a street long problem others would be complaining - and they are not - so if there was a supply defect then more probably it would be in the feed to your home. Is your street fed by overhead lines?

Would you please load up the ring circuits and your sunhouse too (so reconnect the fed to it to the B40A mcb) and then take a rolling pin or hammer and tap the smart meter in a number of places a number of times. Obviously don't beat the living daylights out of it as much as most of us would quire understandably want to at 50p a kWh!

Also wiggle the meter tails to see if their movement causes the trip.

I recall a smart problem in Birmingham when its radio transmissions interfered with the electronics of the rcd causing it to trip - but your rcd does not trip so we will keep that on the back burner for now.

Is the meter cupboard metal or plastic including the door? Is the mobile phone signal strong where you live? How old is the smart meter in the cabinet?

Does the theory still stand when there is no connection to the outgoing side of the mcb ?

Hope it’s not caused by a ham radio station next door

 

[marconi]

Does the theory still stand when there is no connection to the outgoing side of the mcb ?

I wrote - albeit I have edited the text a few times so maybe you did not see it -

Oddly but not physically impossible the sunhouse mcb trips even when it is only connected to the busbar but nothing to its output because the high pulse of magnetic flux(es) from adjacent mcbs link its own short circuit solenoid causing it to trip.

 

[Lewis Curle]

A few questions.
Did you not carry out a full eicr before the board change?
All new colour cables in your photo - a full rewire at some stage, extended circuits or a newish property?
Knowing you have had on going issues, you chose to fit a dual rcd board rather than an rcbo board (and no spd).

My house is 7 years old mate and the sun house is just an extension of the old garage, but the cable feeding the garage is the original cable.
It didn’t even cross my mind to fit an rcbo board to be honest mate.

 

[Lewis Curle]

I am minded - not yet decided since Carlise is half a day's travel each way - to take a look myself so intrigued am I with this problem.

My suspicions have turned to the smart meter. it contains a contactor which isolates the incoming mains in the event of tampering, end of credit, remote supplied command or loss of incoming mains power. The working hypothesis is that there are very brief complete interruptions in mains power to the output terminals of this smart meter caused by some sort of fault associated with this relay or its control including the meter enclosures anti-tamper circuitry. When there is a a very brief interruption in 240Vac when some non-trivial current is being supplied as would be the case when you and /or your wife are using electrical equipment or indeed when fridges and freezers start or run - then the transient currents which flow briefly after power returns to normal causes very high but short duration pulses of magnetic flux in the short circuit solenoid of the mcbs. These pulses of high current high magnetic flux are interpreted by those circuit breakers passing current as short circuits and thus they trip. Oddly but not physically impossible the sunhouse mcb trips even when it is only connected to the busbar but nothing to its output because the high pulse of magnetic flux(es) from adjacent mcbs link its own short circuit solenoid causing it to trip.

These events are initiated and noticeable only when non-trivial currents are flowing thus during gaming, cooking and the use of high power white appliances.

It is still not certain even though the dno have been and tested(? ) that there is no external fault with the distribution network your home connects to noting it is a PME supply. If it was a street long problem others would be complaining - and they are not - so if there was a supply defect then more probably it would be in the feed to your home. Is your street fed by overhead lines?

Would you please load up the ring circuits and your sunhouse too (so reconnect the fed to it to the B40A mcb) and then take a rolling pin or hammer and tap the smart meter in a number of places a number of times. Obviously don't beat the living daylights out of it as much as most of us would quire understandably want to at 50p a kWh!

After this, please take some small plastic clear freezer bags and aluminium foil. Using an mcb as a template cut out two pieces of ally foil shaped to both sides of the mcb. Place these each in a small plastic freezer bag. Interposed these insulated ally sheets between the sides of the mcbs which usually trip. Wait and see what transpires. Obviously take great care that the ally is inside the plastic and does not touch the busbar. No shame if you think this is too risky for you to do. You really do have to be very careful. I only suggest it because you are a qualified electrician. You are making a Faraday shield. See

Faraday cage - Wikipedia - https://en.wikipedia.org/wiki/Faraday_cage

Also wiggle the meter tails to see if their movement causes the trip.

I recall a smart problem in Birmingham when its radio transmissions interfered with the electronics of the rcd causing it to trip - but your rcd does not trip so we will keep that on the back burner for now.

Is the meter cupboard metal or plastic including the door? Is the mobile phone signal strong where you live? How old is the smart meter in the cabinet?

Feel free to come to Carlisle mate you’re most welcome to. I’m currently at work and I have tomorrow planned in for trying things. So I will do as you have asked! I will get the info you have asked for tonight though.

Again thanks for your time in this

 

[marconi]

If I were to travel what's best - weekday or weekend?

 

[pc1966]

When there is a a very brief interruption in 240Vac when some non-trivial current is being supplied as would be the case when you and /or your wife are using electrical equipment or indeed when fridges and freezers start or run - then the transient currents which flow briefly after power returns to normal causes very high but short duration pulses of magnetic flux in the short circuit solenoid of the mcbs.

While that sounds plausible in theory, I really doubt any home system is going to produce that big a magnetic field. Indeed if it did, I would expect to see bent steel enclosures!

 

[marconi]

While that sounds plausible in theory, I really doubt any home system is going to produce that big a magnetic field. Indeed if it did, I would expect to see bent steel enclosures!

Noted.

To fathom this problem I am being creative in generating the hypothesis to inspire the next line of diagnosis. I can see myself visiting.............

I am more open minded about extraordinary current waveforms of several hundreds of Amperes and short duration with their associated magnetic field/flux. Quirky circumstances causing resonance perhaps and not necessarily at 50Hz but a harmonic or several of them?

I don't care if I am wrong.

 

[Lucien Nunes]

Even short-circuit currents of many kA do not trip adjacent MCBs. I could ask a friend who has a large magnet-charger (i.e. huge electromagnet) to try tripping an MCB with it.

 

[brianmoooore]

In spite of the anticipated reaction and assurances I think a little experiment is due to disprove human interaction before wasting more time on this .

Buy another Wylex B32 MCB (3 or 4 quid)
Swap the B40 for a B32. Don't say a word to anyone but move the sockets on the right to the new B32 on the left (along with the respective neutrals) and connect the summer house to the empty B32 on the right (and move the neutral too). This is all temporary.
See if the the same breaker keeps tripping.

If the problem moves to the right without anyone else knowing then it's an electrical problem that is foxing the finest electricians I know.
If the problem stays on the left I'm afraid it's most likely to be a human interaction issue.

This is the next thing that should be done. See if the fault stays with the MCB or moves with the circuit.
Same technique is often used to sort a misfire on an engine. Move the ignition coil or the injector, and see if the fault follows the component or stays with the cylinder.

 

[timhoward]

@marconi I've driven from Eastbourne to Carlisle several times having lived in both places. Granted once was in an LDV Pilot with a cat and a 2 year old for company which is a combination of vehicular technology and company I never want to do again. Whether the differential or the cat made more noise is open to debate. But my point is that if it were me I'd want to rule out human intervention before travelling.
(But if you do go to Carlisle - I'd suggest you'd enjoy a visit to Bookcase on Castle Street which is the best 2nd hand bookshop spread over many floors I've ever found, all properly organised like a library)

 

[nicebutdim]

@marconi I've driven from Eastbourne to Carlisle several times having lived in both places. Granted once was in an LDV Pilot with a cat and a 2 year old for company which is a combination of vehicular technology and company I never want to do again. Whether the differential or the cat made more noise is open to debate. But my point is that if it were me I'd want to rule out human intervention before travelling.
(But if you do go to Carlisle - I'd suggest you'd enjoy a visit to Bookcase on Castle Street which is the best 2nd hand bookshop spread over many floors I've ever found, all properly organised like a library)

I'd wager the cat was significantly more responsive than the steering in that LDV.

 

[mainline]

I think we all need to get our heads together on this one.
So what I propose is all chip in and hire a coach, we can all meet up and go together a few pub stops on the way.

 

[mainline]

I think we all need to get our heads together on this one.
So what I propose is all chip in and hire a coach, we can all meet up and go together a few pub stops on the way.

Tim can bring his self calibrated Megger and I'll bring some southern comfort.