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]

Corsair CX750M (2021) Power Supply Review - https://www.tomshardware.com/reviews/corsair-cx750m-2021-power-supply-review/2

The inrush current from cold start at 230V ac for a single Corsair cx750M bronze according to tomsharware is circa 90A. It could be higher if the capacitors are charged such that their voltage adds to the mains.

 

[Lewis Curle]

Corsair CX750M (2021) Power Supply Review - https://www.tomshardware.com/reviews/corsair-cx750m-2021-power-supply-review/2

The inrush current from cold start at 230V ac for a single Corsair cx750M bronze according to tomsharware is circa 90A. It could be higher if the capacitors are charged such that their voltage adds to the mains.

Ok mate thanks for looking into this! I am going to test the theory of the my pc set up now being plugged in for a couple days to see if it trips. It will give it chance to discharge fully as well.

I have fully reconnected the two DBS involved to make sure it alls all tight and it tripped shortly after redoing it.

So another thing checked of the list! I will keep you informed if my discoveries

 

[Lewis Curle]

Corsair CX750M (2021) Power Supply Review - https://www.tomshardware.com/reviews/corsair-cx750m-2021-power-supply-review/2

The inrush current from cold start at 230V ac for a single Corsair cx750M bronze according to tomsharware is circa 90A. It could be higher if the capacitors are charged such that their voltage adds to the mains.

So I’ve done some testing over the past couple of days.

I totally unplugged my pc set up for two days, in that time the garage MCB has not tripped once. I spent a night in there with some mates and we had the space heater, all the lights and had things like phones charging and the MCB stayed on with no issues.

I’ve been back in tonight to try and game, I got home around 6pm. Turned my pc on and had it play a YouTube video whilst I ate and put my kid to bed. It was on for around two hours but I wasn’t at the pc, I went in to game just before 8 and within 5 minutes of me playing not even a strenuous game the breaker tripped.

So my question is now, does a pc pull more power when playing games? I assume it does when playing a graphics intensive game. So what I am now doing is having my pc plugged in alone with no monitors, just on standby to see if the MCB will trip. If this is the case I’m going to maybe move my pc back into the house for a few days to see if it trips anything.

My worry is that I move it back into my house and it just works with no issues because I don’t know where to go if that’s the case. I would rather it was the PCs power unit just so i can change it and be done with all of this

I hope all of that made sense and would appreciate any more advice you may have sir.
Thanks, Lewis

 

[marconi]

Thank you for the update. I will have a think and let you know tomorrow. Just speaking generally, as computers work harder at number crunching their power consumption will increase. This is of course what is happening in video games especially those with high fidelity graphics and game physics ie dealing with motion, collisions, interactions with objects and background and not forgetting the player(s) input.

How many Corsair power units where powered up and supplying when you tried a game this evening?

And to be clear which mcb tripped?

Please tell me the type of the 40A MCB which supplies the sunhouse and also the rating and type of the mcb for the ring in sunhouse. Eg 40A type B and 32A type B? It may be the waveform of the current drawn by the corsairs power supplies has a form which has a high crest factor which means it has a high peak current compared to the average current. If this is the case The MCBs responds to waveform as if this was a short circuit And trips. But this is my thinking at the moment So no changes yet please.

how long is the cable run from house db to sunhouse db? What mm2 is the cable? Volt drop with increasing current may be a factor. The Corsair has an input voltage range something like 100 to 230V without the need to change any settings. What happens is that at lower voltages the current increases as required to deliver the same power output.

ps: crest factor is peak current/rms current

 

[James]

Can you post a picture of the 40A breaker that is tripping?

 

[nicebutdim]

Can you post a picture of the 40A breaker that is tripping?

Been thinking, perhaps, along similar lines, but scrolled up and see the OP posted images in #6. It is indeed a 40A MCB.

 

[Lewis Curle]

Thank you for the update. I will have a think and let you know tomorrow. Just speaking generally, as computers work harder at number crunching their power consumption will increase. This is of course what is happening in video games especially those with high fidelity graphics and game physics ie dealing with motion, collisions, interactions with objects and background and not forgetting the player(s) input.

How many Corsair power units where powered up and supplying when you tried a game this evening?

And to be clear which mcb tripped?

Please tell me the type of the 40A MCB which supplies the sunhouse and also the rating and type of the mcb for the ring in sunhouse. Eg 40A type B and 32A type B? It may be the waveform of the current drawn by the corsairs power supplies has a form which has a high crest factor which means it has a high peak current compared to the average current. If this is the case The MCBs responds to waveform as if this was a short circuit And trips. But this is my thinking at the moment So no changes yet please.

how long is the cable run from house db to sunhouse db? What mm2 is the cable? Volt drop with increasing current may be a factor. The Corsair has an input voltage range something like 100 to 230V without the need to change any settings. What happens is that at lower voltages the current increases as required to deliver the same power output.

ps: crest factor is peak current/rms current

The MCB in the home DB feeding the garage is a 40A type B that is using a 6mm core live and a bunch of little neutrals. Inside the sun house itself it’s on a 16A MCB currently. The original circuit in the sun house was just a 16A radial, but I changed it to a ring and made the MCB a 32A for a while but I have since changed it back to the 16A(all type Bs)

I made the change because I wanted to be able to have more on the circuit, without it being an issue. I have changed it back to a 16A MCB but I’ve left it as a ring instead of the radial. It’s been about three weeks since I made the move Into the sun house and it worked for about two weeks and now this issue has been going on for a week.

I’m confident the cabling is all good in the sun house and the cable going to the sun house has tested out good as well. I put it out of my mind that my PC set up could be the issue since it’s worked perfectly when it was in my house on the upstairs ring main.

I’m having my brother round on Thursday and he is bringing his pc. He’s going to plug his pc into my setup and see if we have the same issue. If we don’t then it just be my pc.

Thanks all for your replies! I really do appreciate you taking the time to help me out.

 

[marconi]

Do you have a fridge in the sun house?

 

[Lewis Curle]

Do you have a fridge in the sun house?

I do but it and the freezer is not plugged in, hasn’t been for a while!

 

[marconi]

How many Corsair power units where powered up and supplying when you tried a game yesterday evening?

Do you have LED lighting in the sunhouse? If you do how many lamps? Are they normally on when you are gaming?

LED lamps have a high crest factor waveform too.

I will await your post after Thursday's trial.

 

[marconi]

If you look at ‘Test results - Final thoughts’ you can see a table showing some test data for your Corsair PSu for different game loads and see how power consumption increases with game computing load.

Corsair CX750M 750W 80 PLUS Bronze Power Supply Review - https://www.tweaktown.com/reviews/7125/corsair-cx750m-750w-80-plus-bronze-power-supply-review/index.html

 

[Lewis Curle]

If you look at ‘Test results - Final thoughts’ you can see a table showing some test data for your Corsair PSu for different game loads and see how power consumption increases with game computing load.

Corsair CX750M 750W 80 PLUS Bronze Power Supply Review - https://www.tweaktown.com/reviews/7125/corsair-cx750m-750w-80-plus-bronze-power-supply-review/index.html

So I did some digging into what my pc can use in terms of power.

Over the last 6 months I’ve changed the graphics card to a 3070ti. Added a 2 TB SDD and changed the water cooling system to a fan (the water cooling killed my old graphics card from leaking, was a nightmare so I got rid).

After doing the power calculations it recommended I should have a 700W power supply and that’s without taking into account all my USBs plugged in for mouse and keyboard etc.

I also had my brother round last night and he used his pc in my setup and it worked for 3 hours no issues playing intensive games. So straight away I bought myself a new 1000W CPU so it had the power for sure and to make sure it wasn’t my 750W PSU causing the issue. I was pretty confident that changing the PSU would fix my issue. It’s arriving tommorow so I’m going to try it but my confidence was knocked when I got home today and the 40A MCB was off. All of my screens and cables were plugged in at the wall but none of it was turned on and my PC is currently in bits in the table so that definitely wasn’t plugged in.

I’m just a bit confused now as it always seems like my pc was causing the issue but now I’m not convinced. My partner has had a busy day in the house using a lot of the white goods units(washing machine, dryer and dishwasher), kettle and what not.

But I can’t see how if any of that was causing an issue. That the 40A MCB for the garage would be the only circuit to trip when there was literally no load going down the cable.

As I say I’m going to change my PSU anyway to make sure but I’m doubtful that’s the issue now. I’ll let you know how it goes. Thanks for reading!

 

[marconi]

Ta. Will have a ponder. I have been thinking about sending you a simple circuit to detect a L-N arc ie a brief short circuit. I will say more tomorrow. I suspect the cable between the house db and the sunhouse db has an L-N defect.

I need to have a rummage in my den for some components tomorrow.

 

[Lewis Curle]

Ta. Will have a ponder. I have been thinking about sending you a simple circuit to detect a L-N arc ie a brief short circuit. I will say more tomorrow. I suspect the cable between the house db and the sunhouse db has an L-N defect.

I need to have a rummage in my den for some components tomorrow.

Alright mate take your time, appreciate it though. I might run a temp cable from the house to the garage to see what that will do.

 

[marconi]

If you have the time and inclination would you disconnect the sunhouse cable completely at both ends and then separate the blue neutrals at both ends.

Then would you do some pair-wise insulation resistance checks of the blue neutral conductors using as as a guide what I have shown in the attachment. The 6mm2 scc has 7 blue neutrals wrapped around it.

I am just wondering whether the cable is damaged and if this damage includes individual neutral cores coming into contact. If this unintended contact is present then maybe whatever has caused it has also damaged the insulation of the central brown conductor at the same place.