Strange RCD tripping problem

[Mjbarnard]

Ok thanks. So does that mean I might be able to get the supply split and put the A/C on a new mini CU?

 

[Pete999]

Ok thanks. So does that mean I might be able to get the supply split and put the A/C on a new mini CU?

I would get the A/C wiring tested before you go to the expense of an all RCBO board, or any other expensive moves, seen a lot of A/C electrics thrown in by so called engineers, if it works that's good enough in most cases, how many A/C engineers have you seen with a MFT?

 

[derek]

I would get the A/C wiring tested before you go to the expense of an all RCBO board, or any other expensive moves, seen a lot of A/C electrics thrown in by so called engineers, if it works that's good enough in most cases, how many A/C engineers have you seen with a MFT?

The absence of an MFT could be why there was no Electrical Installation Certificate provided by the A/C installers (that is if I have read the thread correctly).
I would have expected the A/C engineer to provide a resistance value and which cores of the circuit had faults on, in their report identifying the D/w circuit as the culprit.

 

[Mjbarnard]

As you can see (or perhaps not), not a very technical report

 

[Ian Mills]

Hpi type:

Modular devices Hpi type RCCBs - http://www.export.legrand.com/EN/modular-devices-hpi-type-rccbs_63.html

Hpi seem similar to UK type B RCCB - not sure yet if they are the same.

Hi think a little different, we also have type B here but all I have seen are 3 phase but sure must be other single phase out there, would think type b would be okay for this application

 

[Mjbarnard]

UPDATE to this perplexing problem. I am grateful to everyone for their time and contributions.

An expert visited a couple of weeks ago. He found that the problem was not over-current, rather accumulated earth leakage - as has been suggested by some above - and a Neutral-Earth fault on the downstairs ring - there was a nicked blue wire in the metal back box of the dishwasher socket.

Additionally and exacerbating, the earth conductors in the kitchen 9 gang DP switch plate (which includes the dishwasher circuit) were not properly connected together and one actually appeared damaged with blackening.

He fixed these faults and then installed 32A RCBOs for the two air con units because there were brief surges in earth leakage when each unit was energised: once energised their earth leakage was small. These brief surges when added to the accumulated earth leakage were detected as excessive by RCD2.

Since this was done we have had no further trips. It has only been two weeks, so I understand it might yet recur, but suffice to say that we have not been able to have both aircon circuits on at the same time for several months so something has definitely changed.

Thanks again to everyone. I am hoping this problem is solved - time will tell.

 

[Octopus]

^^ Good man .......... I really appreciate your feedback - so few people do this and its good to hear that it seems to have been resolved.

Dual RCD boards have certainly not helped - with more and more devices in a house adding to "natural" leakage, so a small fault can push an RCD over the limit.

 

[ruston]

Yes , thanks for letting us know . I hope it is now sorted for you.