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

 

[davesparks]

They passed with the max reading off the tester. So when you say it will not discriminate on a fault what do you mean? The MCBs in the garage board have never tripped it’s always the 40A MCB one. So if there was an overload somehow being caused it would trip the 16A one first no?

Thanks for your reply though mate

By not discriminate I mean if there is a fault then there is no guarantee that the 16A MCB will operate before the 40A MCB.
If it is an overload then the 16A will operate first yes.

 

[pc1966]

Example table from Hager. Not quite your case, but if you had a 40A B-curve MCB feeding a 16A B-curve RCBO then any prospective fault above 0.19kA = 190A is likely to trip both devices:

 

[Lewis Curle]

Fault discrimination, now known as selectivity, is the ability of a cascade of protective devices to only trip the closest to the fault.

In the case of MCB they are selective on overloads that take time on the thermal trip side (so up to x3 or so from the rated value of the upstream device) but if you get a big fault, such as a short-circuit, then both devices would have the "instant" magnetic trip underway before the downstream device has actually opened and isolated the fault. Basically in many case both devices trip.

When cascading breakers when it matters, you need to add a short delay on the upstream device to give the downstream one time to act, but if it does not (or the fault is before it) then the upstream will go. Usually that means using a MCCB (at high cost) or a fuse (cheap, effective, but a pain to replace and typically means electrically-skilled staff).

If you look at commercial/industrial catalogues of electrical devices they often will have tables in the back giving you the selectivity limits for various combinations of fuse/MCB, MCCB/MCB, MCB/MCB and so on.

So after reading all that and thanks for the information, it looks like the fault is happening from the main DB in my house to the little one in the garage? Since the garage ones never trip it just be occurring before those MCBs are involved?

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. The most confusing part to me is other MCBs have been going off as well.

Thanks for you time again

 

[pc1966]

So after reading all that and thanks for the information, it looks like the fault is happening from the main DB in my house to the little one in the garage? Since the garage ones never trip it just be occurring before those MCBs are involved?

It looks that way.

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. The most confusing part to me is other MCBs have been going off as well.

It is just possible that a big fault on one circuit causes enough of a surge on another that it also trips.

But they would go simultaneously to all intents and purposes, and it is odd to have that without some evidence of poor IR readings.

 

[Lewis Curle]

It looks that way.


It is just possible that a big fault on one circuit causes enough of a surge on another that it also trips.

But they would go simultaneously to all intents and purposes, and it is odd to have that without some evidence of poor IR readings.

Alright mate well I’ll do another IR test tonight on the circuit, just to be sure. I’ll keep you informed on my findings!

 

[UNG]

So the last time I saw a fault like / similar to this was around 35 or so years ago and the memory is a little bit hazy about it but I do recall the problem ended up as a DNO distribution issue

Now to get a bit more background where is this property located is it urban, semi rural or rural, how is the supply delivered is it underground or overhead,

Does this random tripping occur more or only during episodes of wet weather

What connected loads does the garage have, are there any PIR controlled outdoor lights supplied from the garage

While trying to identify the fault have you done any random voltage checks of the main supply at different times to see if there are any large variations that may suggest an external mains issue

 

[Lewis Curle]

So the last time I saw a fault like / similar to this was around 35 or so years ago and the memory is a little bit hazy about it but I do recall the problem ended up as a DNO distribution issue

Now to get a bit more background where is this property located is it urban, semi rural or rural, how is the supply delivered is it underground or overhead,

Does this random tripping occur more or only during episodes of wet weather

What connected loads does the garage have, are there any PIR controlled outdoor lights supplied from the garage

While trying to identify the fault have you done any random voltage checks of the main supply at different times to see if there are any large variations that may suggest an external mains issue

Hello mate thanks for your message.
I live in an semi urban set of new builds on the outside of town. I’m pretty sure all the cables are ran underground because there’s a subby not 100ft from my house.

I do have an outside light that hasn’t work for some time now that is on a pir, I didn’t think to look at that since the 6A MCB baby ever tripped that controls it. I will diss connect it tonight to test!

As far as the voltage checks I seem to get a level 240V when I’ve checked, but I will double check again to be sure!

Cheers, Lewis

 

[marconi]

Hello. Please would you tell me:

1. The make, model and power of your gaming PSU. Do you have more than one?
2. Do you plug them directly into a socket or via a surge suppression socket strip?
3. When you say nothing is on do you mean the PC, IT and gaming equipment including PSU is switched off on the equipment or at the socket?
4. Co-incident with moving the equipment to the sunhouse have you added any equipment or changed any of it?
5. Have you tried leaving the 40A mcb off for a few days to isolate power to the sunhouse and the equipment in there?
6. What white goods do you have ie washer, dryer, dishwasher and microwave? Have these changed recently?
7. Do you have an induction hob?
8. Have you had a smart meter fitted recently or at all?
9. Do your lights ever flicker? Do your neighbours ever?
10. Has any digging been done in the garden near the cable to the sunhouse?
11. Have you had any water leaks or rain water ingress to your home of sunhouse?
12. Who did the electricity supply to the sunhouse? Do you have a test certificate if it was done after the main house? How long is the cable run?
13. Would you say the problem never happened until the shift of equipment to the sunhouse?
14. Do you have an electric vehicle charger?
15. What exactly is fed by each circuit breaker - a labelled picture would be helpful.
16. Do you have air conditioning units or heat pumps?
17. Please post a picture of your supply intake and meter.

My hypothesis is you have a loose line, neutral or earth connection(s) - within or without your property - which is causing high dV/dt of the supply voltage; a or several connected loads have mains filters within them which are reacting to the high dV/dt with a high albeit brief current as their capacitors change their state of charge. I suspect the circuit for the sunhouse since it has used unusually split concentric cable which needs care terminating well. The reliable conduction of a connection or joint can vary with current density.

 

[Lewis Curle]

Hello. Please would you tell me:

1. The make, model and power of your gaming PSU. Do you have more than one?
2. Do you plug them directly into a socket or via a surge suppression socket strip?
3. When you say nothing is on do you mean the PC, IT and gaming equipment including PSU is switched off on the equipment or at the socket?
4. Co-incident with moving the equipment to the sunhouse have you added any equipment or changed any of it?
5. Have you tried leaving the 40A mcb off for a few days to isolate power to the sunhouse and the equipment in there?
6. What white goods do you have ie washer, dryer, dishwasher and microwave? Have these changed recently?
7. Do you have an induction hob?
8. Have you had a smart meter fitted recently or at all?
9. Do your lights ever flicker? Do your neighbours ever?
10. Has any digging been done in the garden near the cable to the sunhouse?
11. Have you had any water leaks or rain water ingress to your home of sunhouse?
12. Who did the electricity supply to the sunhouse? Do you have a test certificate if it was done after the main house? How long is the cable run?
13. Would you say the problem never happened until the shift of equipment to the sunhouse?
14. Do you have an electric vehicle charger?
15. What exactly is fed by each circuit breaker - a labelled picture would be helpful.
16. Do you have air conditioning units or heat pumps?
17. Please post a picture of your supply intake and meter.

My hypothesis is you have a loose line, neutral or earth connection(s) - within or without your property - which is causing high dV/dt of the supply voltage; a or several connected loads have mains filters within them which are reacting to the high dV/dt with a high albeit brief current as their capacitors change their state of charge. I suspect the circuit for the sunhouse since it has used unusually split concentric cable which needs care terminating well.

Wow thanks for taking the time to write all that.

Hello. Please would you tell me:

1. The make, model and power of your gaming PSU. Do you have more than one?
2. Do you plug them directly into a socket or via a surge suppression socket strip?
3. When you say nothing is on do you mean the PC, IT and gaming equipment including PSU is switched off on the equipment or at the socket?
4. Co-incident with moving the equipment to the sunhouse have you added any equipment or changed any of it?
5. Have you tried leaving the 40A mcb off for a few days to isolate power to the sunhouse and the equipment in there?
6. What white goods do you have ie washer, dryer, dishwasher and microwave? Have these changed recently?
7. Do you have an induction hob?
8. Have you had a smart meter fitted recently or at all?
9. Do your lights ever flicker? Do your neighbours ever?
10. Has any digging been done in the garden near the cable to the sunhouse?
11. Have you had any water leaks or rain water ingress to your home of sunhouse?
12. Who did the electricity supply to the sunhouse? Do you have a test certificate if it was done after the main house? How long is the cable run?
13. Would you say the problem never happened until the shift of equipment to the sunhouse?
14. Do you have an electric vehicle charger?
15. What exactly is fed by each circuit breaker - a labelled picture would be helpful.
16. Do you have air conditioning units or heat pumps?
17. Please post a picture of your supply intake and meter.

My hypothesis is you have a loose line, neutral or earth connection(s) - within or without your property - which is causing high dV/dt of the supply voltage; a or several connected loads have mains filters within them which are reacting to the high dV/dt with a high albeit brief current as their capacitors change their state of charge. I suspect the circuit for the sunhouse since it has used unusually split concentric cable which needs care terminating well. The reliable conduction of a connection or joint can vary with current density

Hello. Please would you tell me:

1. The make, model and power of your gaming PSU. Do you have more than one?
2. Do you plug them directly into a socket or via a surge suppression socket strip?
3. When you say nothing is on do you mean the PC, IT and gaming equipment including PSU is switched off on the equipment or at the socket?
4. Co-incident with moving the equipment to the sunhouse have you added any equipment or changed any of it?
5. Have you tried leaving the 40A mcb off for a few days to isolate power to the sunhouse and the equipment in there?
6. What white goods do you have ie washer, dryer, dishwasher and microwave? Have these changed recently?
7. Do you have an induction hob?
8. Have you had a smart meter fitted recently or at all?
9. Do your lights ever flicker? Do your neighbours ever?
10. Has any digging been done in the garden near the cable to the sunhouse?
11. Have you had any water leaks or rain water ingress to your home of sunhouse?
12. Who did the electricity supply to the sunhouse? Do you have a test certificate if it was done after the main house? How long is the cable run?
13. Would you say the problem never happened until the shift of equipment to the sunhouse?
14. Do you have an electric vehicle charger?
15. What exactly is fed by each circuit breaker - a labelled picture would be helpful.
16. Do you have air conditioning units or heat pumps?
17. Please post a picture of your supply intake and meter.

My hypothesis is you have a loose line, neutral or earth connection(s) - within or without your property - which is causing high dV/dt of the supply voltage; a or several connected loads have mains filters within them which are reacting to the high dV/dt with a high albeit brief current as their capacitors change their state of charge. I suspect the circuit for the sunhouse since it has used unusually split concentric cable which needs care terminating well. The reliable conduction of a connection or joint can vary with current density.

Hello mate first of all thanks for taking the time to write all that!

So I’m unsure on my PSU model I will find out tonight
2.

Hello. Please would you tell me:

1. The make, model and power of your gaming PSU. Do you have more than one?
2. Do you plug them directly into a socket or via a surge suppression socket strip?
3. When you say nothing is on do you mean the PC, IT and gaming equipment including PSU is switched off on the equipment or at the socket?
4. Co-incident with moving the equipment to the sunhouse have you added any equipment or changed any of it?
5. Have you tried leaving the 40A mcb off for a few days to isolate power to the sunhouse and the equipment in there?
6. What white goods do you have ie washer, dryer, dishwasher and microwave? Have these changed recently?
7. Do you have an induction hob?
8. Have you had a smart meter fitted recently or at all?
9. Do your lights ever flicker? Do your neighbours ever?
10. Has any digging been done in the garden near the cable to the sunhouse?
11. Have you had any water leaks or rain water ingress to your home of sunhouse?
12. Who did the electricity supply to the sunhouse? Do you have a test certificate if it was done after the main house? How long is the cable run?
13. Would you say the problem never happened until the shift of equipment to the sunhouse?
14. Do you have an electric vehicle charger?
15. What exactly is fed by each circuit breaker - a labelled picture would be helpful.
16. Do you have air conditioning units or heat pumps?
17. Please post a picture of your supply intake and meter.

My hypothesis is you have a loose line, neutral or earth connection(s) - within or without your property - which is causing high dV/dt of the supply voltage; a or several connected loads have mains filters within them which are reacting to the high dV/dt with a high albeit brief current as their capacitors change their state of charge. I suspect the circuit for the sunhouse since it has used unusually split concentric cable which needs care terminating well. The reliable conduction of a connection or joint can vary with current density.

I will put my pc details in the chat for you to see sir! First of all thanks for taking the time to write all that.
1. See picture
2. It is all plugged in via a surge suppression strip, i have only changed that as of a couple of days ago and the issue is still happening.
3.I leave my PC and everything plugged in and turned on at the socket.
4. My PC has never tripped the inside circuits of my house before, The garage in the past has been found with the MCB off but never this much.
5. I havent left it off for more than a day no.
6. Yeah we have all of the above but no they have not been touched since we moved in.
7. We have a Gas hob
8. We have a smart meter just plugged into the sockets in the kitchen, we have recently plugged it back in a few weeks ago, however i unplugged it again to see if it was causing the issue and it appears to not have had any effect as its still tripping.
9.Not that i know off.
10. No digging has been done since we moved in,
11.No water that i can tell.
12.Its definitely gotten worse since the equipment was moved in, But we have used the sun house a lot in the past and i must say it was rarely off but it has happened.
13.Not never happened just happening a lot more now.
14. NO
15. The 40A one in the picture is the garage one but ill get a laballed pictuire.
16.No
17. I will get those photos.

Thanks hope that helps please ask any more questions that you want to. I appreciate the help!


Also i redone the IR test and took the dodgy outside light down and its still tripping. The IR test again came back perfect.

 

[Lewis Curle]

Hello. Please would you tell me:

1. The make, model and power of your gaming PSU. Do you have more than one?
2. Do you plug them directly into a socket or via a surge suppression socket strip?
3. When you say nothing is on do you mean the PC, IT and gaming equipment including PSU is switched off on the equipment or at the socket?
4. Co-incident with moving the equipment to the sunhouse have you added any equipment or changed any of it?
5. Have you tried leaving the 40A mcb off for a few days to isolate power to the sunhouse and the equipment in there?
6. What white goods do you have ie washer, dryer, dishwasher and microwave? Have these changed recently?
7. Do you have an induction hob?
8. Have you had a smart meter fitted recently or at all?
9. Do your lights ever flicker? Do your neighbours ever?
10. Has any digging been done in the garden near the cable to the sunhouse?
11. Have you had any water leaks or rain water ingress to your home of sunhouse?
12. Who did the electricity supply to the sunhouse? Do you have a test certificate if it was done after the main house? How long is the cable run?
13. Would you say the problem never happened until the shift of equipment to the sunhouse?
14. Do you have an electric vehicle charger?
15. What exactly is fed by each circuit breaker - a labelled picture would be helpful.
16. Do you have air conditioning units or heat pumps?
17. Please post a picture of your supply intake and meter.

My hypothesis is you have a loose line, neutral or earth connection(s) - within or without your property - which is causing high dV/dt of the supply voltage; a or several connected loads have mains filters within them which are reacting to the high dV/dt with a high albeit brief current as their capacitors change their state of charge. I suspect the circuit for the sunhouse since it has used unusually split concentric cable which needs care terminating well. The reliable conduction of a connection or joint can vary with current density.

 

[marconi]

Thank you.

For now it would be helpful if you opened up each CU (House and sun house) and with power off carefully inspect where the lower terminals of mcbs connect to busbar to confirm they are clamping or being screwed onto busbar. Tighten up all lower mcb screws and note down any which appeared loose. Do the same for RCDs and mains switches

Check solidity and security of neutral and cpc connections by tug and wiggle check. Again note any loose ones and tighten up. While you are at it remake the neutrals for the split concentric at the house CU.

With all sunhouse IT and gaming powered up go to intake and meter board and gently wiggle - not tug - the tails and feeds. Any trips?

Is the surge socket strip a simple type with a glowing neon or is it a professional one which contains inductors, capacitors and over voltage protection Eg by Olson?

Try plugging your sunhouse IT and gaming equipment directly into mains instead of via the surge socket strip. Leave for say a few days or until another mob trip happens.

Try leaving your IT and gaming equipment unplugged from mains for a few days or until trip happens.

Try turning off main switch of sunhouse CU but house 40A mob on for a few days or until trip happens.

What is the answer to 12 please? I will not give you a hard time if it was you.

Probably enough for now.

 

[Lewis Curle]

Thank you.

For now it would be helpful if you opened up each CU (House and sun house) and with power off carefully inspect where the lower terminals of mcbs connect to busbar to confirm they are clamping or being screwed onto busbar. Tighten up all lower mcb screws and note down any which appeared loose. Do the same for RCDs and mains switches

Check solidity and security of neutral and cpc connections by tug and wiggle check. Again note any loose ones and tighten up. While you are at it remake the neutrals for the split concentric at the house CU.

With all sunhouse IT and gaming powered up go to intake and meter board and gently wiggle - not tug - the tails and feeds. Any trips?

Is the surge socket strip a simple type with a glowing neon or is it a professional one which contains inductors, capacitors and over voltage protection Eg by Olson?

Try plugging your sunhouse IT and gaming equipment directly into mains instead of via the surge socket strip. Leave for say a few days or until another mob trip happens.

Try leaving your IT and gaming equipment unplugged from mains for a few days or until trip happens.

Try turning off main switch of sunhouse CU but house 40A mob on for a few days or until trip happens.

What is the answer to 12 please? I will not give you a hard time if it was you.

Probably enough for now.

Ok mate i will do as you say at some point today and come back with results!

The surge protection strip is LOGIK which i think is just a standard one of the shelf electrical wholesalers.

I will try and see if the error occurs when nothing is plugged into the sunhouse, Can a bad PC power unit cause things like this to happen?

So the cable to the sunhouse i know little about as it was all here when we moved in. The sun house is an extension of the old garage so i imagine the its the original cable from when the whole place was built. I have considered wiring a temp 6mm SWA from my DB to the garage. To see if the duct or something is crushing the cable underground where i cant see but surely any issues would show up on the testing i have done?

Again thanks for taking the time i will get back to you later today

 

[marconi]

High performance high power Pc and gaming power supplies do not last forever. They contain capacitors which are worked hard and run hot which reduces their life. One might expect 20000 hours life from the PSU but considerably less if the PSu is left on all the time. One sign of failing capacitors is mcb tripping. How old are your power supplies and do you leave them powered up all the time? Mcbs often trip faster than fuses rupture.
This is why some time with your equipment unplugged would be helpful.

what is the ambient temperature like in your sunhouse? Does it get quite warm at times or has it in the past ie over say 18-21C? Are the fans working and any filters clear of dust And unobstructed? Check there is good air flow around PSus and that one does not suck in the hot air from the other.

Last, these sort of power supplies have high inrush current when turned on. The value depends on where in the mains cycle they are energised and the state and polarity of charge on the capacitor. If there was a loose connection then it could be inrush current is tripping the mcb.

 

[Bob Geldoff1234]

It might be worth ruling out faulty breakers.The 40amp one could be very sensitive and the others that trip randomly could be going the same way.Maybe worth swapping out the 40amp breaker for a new one to see if that cures it?

 

[Lewis Curle]

It might be worth ruling out faulty breakers.The 40amp one could be very sensitive and the others that trip randomly could be going the same way.Maybe worth swapping out the 40amp breaker for a new one to see if that cures it?

I’ve already swapped it out mate! But thanks for the advice