2 rcd tripped twice for no reason

[JohnW2]

Are these two breakers that trip adjacent to each other?? ... One circuit may have a genuine fault and the MCB may be getting hot and causing the other one to heat up and trip out even though there may be no failure on that MCB's circuit.

Interesting thought, although I think that would be much more probable in a modern CU with DIN-rail-mounted MCBs, in contact with one another. Those plug-in Wylex MXBs usually have significant air gaps between them, so I would imagine that one would have to get extremely hot before it would cause the adjacent one to operate. However, who knows?! EFLI's idea about two ring final sockets circuits being cross-connected, and some intermittent fault (goodness knows what) being on just one of them, sounds perhaps a more likely explanation for simultaneous operation of both devices. ...

mack10: If you switch off just one of those two MCBs, does the corresponding circuit lose its power, or do you have to switch both MCBs off for either circuit to lose power?

My educated guess is that the kitchen circuit got overloaded at Sunday lunch time (cooker / washer/ kettle/ ??) and tripped the adjacent breaker.

Possibly, although it seems very odd that it's happened more than once today, but hasn't happened during the previous many years.

Kind Regards, John

 

[mack10]

Yes I got an electrician to look at it he confirmed that the upstairs plug ring and the downstairs ring are cross . Somewhere but said the a faults must have developed since it has been ok for seven years up initials yesterday.

Anybody got any ideas I have tested all,sockets and switched everything off and pulled all plugs and it still trips. The heating timer is in the bedroom and a power shower is on the upstairs ring and they are hard wired so just switched them off. So I have nothing plugged in and no appliances with power. what could be causing it to trip. I presume even if I fix the ring to make them separate circuits I will still have the fault. I checked all the sockets, while it staying on for a while, with a socket tester and they all hand 3 lights lit.

I have someone coming tomorrow to give me a quote to sort the rings out and the. Hopefully the fault. any ideas how much this will cost?

 

[JohnW2]

Yes I got an electrician to look at it he confirmed that the upstairs plug ring and the downstairs ring are cross . Somewhere but said the a faults must have developed since it has been ok for seven years up initials yesterday.

Clever EFLI!

I presume even if I fix the ring to make them separate circuits I will still have the fault.

Yes, I'm afraid that's the case. The crossed circuits have probably 'always' been there, but a fault has arisen which has brought that to light.

I have someone coming tomorrow to give me a quote to sort the rings out and the. Hopefully the fault. any ideas how much this will cost?

I think you can guess how helpless we are to answer that one. If (perhaps the most likely) the circuits are 'crossed' within your CU, then sorting that out will be very quick (hence not very costly). However, if the circuits are cross-connected somewhere within the wiring of the sockets, that could (but might not) take a long time to locate. Similarly, the hunt for (and rectification of) the fault could either be quick or protracted. Sorry for not being very helpful!

Kind Regards, John

 

[EFLImpudence]

As both breakers trip at the same time I would think it must be a short circuit between a Live wire and a Neutral wire ,a CPC (earth wire) or an earthed metal part (e.g. a pipe).

It could happen due to movement somewhere because of heating/cooling or pressure.


Difficult to find. No telling how long it will take.


At least, with the rings separated it will halve the places to look.

 

[JohnW2]

As both breakers trip at the same time I would think it must be a short circuit between a Live wire and a Neutral wire ,a CPC (earth wire) or an earthed metal part (e.g. a pipe).

Indeed. If both B32s are tripping magnetically (which seems probable if they are tripping simultaneously) that implies a fault current of at least 320A.

Well done with your partial diagnosis!

KInd Regards, John

 

[securespark]

Well done with your partial diagnosis!

Very much seconded!

 

[JohnW2]

Well done with your partial diagnosis!

Very much seconded!

I should really have thought of it myself (although I didn't!) because, many moons ago, I experienced almost exactly the same as the OP, the only difference being that it was a 'persistant' fault, rather than an intermittent one. Soon after I moved into my present house, before I had looked seriously at the electrical installation, a washing machine developed an L-N fault which caused the fuses (bad old days!) of two ring final circuits to blow. After a good bit of head scratching (and some practice at rewiring BS3036 fuses!) I discovered that one leg of each of the two circuits had been 'crossed' at the CU.

That was a relatively easy fault to find, given that it first happened when the WM was switched on and every time I switched it back on, both fuses blew - it just took me longer than it should have done to fathom out why both fuses were blowing! In the OP's case, the intermittent nature of the fault could, unfortunately, make it much more difficult to locate.

Kind Regards, John