MCBs Tripping Intermittantly

[Andrew Gordon]

I have an intermittant problem with 2 x 32A MCBs tripping in the house. The downstairs Sockets MCB is tripping and the Cooker MCB is tripping intermittantly at the same time.
I have checked, all plugged in appliances and I suspected an oil heater which I unplugged. Everything was fine until a week later. The Cooker and Socket MCB tripped again both of them. The cooker point was being used when it tripped. The Cooker outlet has an isolator switch and a switched socket which is used for running a kettle in the kitchen. Suspecting an issue with the Cooker point nothing has been plugged into it for over a week and it hasnt tripped. Any ideas? Why would 2 separate circuits trip together?

 

[securespark]

Are the two MCB's adjacent?

 

[JohnW2]

I have an intermittant problem with 2 x 32A MCBs tripping in the house. The downstairs Sockets MCB is tripping and the Cooker MCB is tripping intermittantly at the same time. .... Why would 2 separate circuits trip together?

They shouldn't do. If, as you seem to be saying, MCBs on what are meant to be totally separate circuits are tripping simultaneously, then something is probably very wrong and I would suggest that you should get an electrician to investigate.

Kind Regards, John

 

[Andrew Gordon]

Yes the 2 MCBs are next to each other on the non RCD side of the Consumer unit.

 

[JohnW2]

Yes the 2 MCBs are next to each other on the non RCD side of the Consumer unit.

Fair enough, but as I sort of asked, are they tripping simultaneously? Securespark was presumably thinking that if one is getting overloaded, hot, and tripping as a result, it could possibly affect an adjacent MCB - but if that were the case there would almost certainly be a time lag (even if only small) between when the first and second ones tripped.

Kind Regards, John

 

[Andrew Gordon]

The time lag I have observed is to be a matter of a couple of seconds if that.
What rating should the Cooker MCB supply be? I thought cooker points were 40 Amp or 45 Amp supply

 

[JohnW2]

The time lag I have observed is to be a matter of a couple of seconds if that.

I would doubt that a thermal effect would happen anything like that quickly, but I suppose that nothing is impossible!

What rating should the Cooker MCB supply be? I thought cooker points were 40 Amp or 45 Amp supply

32A is easily the most common, and is adequate for virtually any cooker.

There are really two issues here. For a start, something is wrong to be causing one of the MCBs to trip. Secondly, MCBs on two totally different circuits are tripping in very quick succession. As I said, I think that 'investigation' is probably needed.

Kind Regards, John

 

[Andrew Gordon]

Thanks

 

[flameport]

Loose wire on one of the MCBs causing overheating, heat spreads to the adjacent one causing the same problem there.

 

[JohnW2]

Loose wire on one of the MCBs causing overheating, heat spreads to the adjacent one causing the same problem there.

That's what has been suggested/implied - but, as I said, if that were what was happening, I would have expected more than 'a second or two' between when the first one (with the poor connection, hence heat source) tripped and the heat spread enough to the other one for it to trip, wouldn't you?

Kind Regards, John

 

[bernardgreen]

Secondly, MCBs on two totally different circuits are tripping in very quick succession.

They nay not be separate, if the two Lives are some how connected together then the MCBs will trip in quick succession as is happening.

The connection may be incorrect wiring or damage to two cables that has connected the Lives together. A nail driven into a bunch of cables for example.

As said this needs investigation

 

[JohnW2]

They nay not be separate, if the two Lives are some how connected together then the MCBs will trip in quick succession as is happening.

Exactly my point. That's why I previously described them as "circuits which were meant to be totally separate".

Kind Regards, John