New FB RCCB tripping

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New fb recently with split load (two RCCB)

All ok after installation until i went to operate the microwave which caused the RCCB to trip?

What i noticed was when i went to switch on the tripped RCCCB the opposite RCCB tripped!

Switched them both back on and all ok.

Was fine for a couple of days even with use of the microwave but last night when operating the microwave it tripped again.

Any ideas?

Thanks
 
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Broken microwave, maybe it has an insulation fault.
Were you microwaving something particularly steamy at the time? Baked potato or porridge or something?
 
In that case it's new microwave time, unless it's a really expensive one it's probably not worth getting repaired.
Perhaps the fault has been there a while unnoticed. Now that you've got RCD protection it's spotted the imbalance.
 
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In that case it's new microwave time, unless it's a really expensive one it's probably not worth getting repaired. Perhaps the fault has been there a while unnoticed. Now that you've got RCD protection it's spotted the imbalance.
I would agree with everything you have said, were it not for the following, which makes me wonder ....
New fb recently .... What i noticed was when i went to switch on the tripped RCCCB the opposite RCCB tripped!
Does not this not suggest some sort of cross-connection between circuits on the two 'sides' of the new CU - perhaps due to a wiring error when the CU was recently installed? Although one can postulate mechanisms whereby a N-E fault on one set of circuits can theoretically cause an RCD protecting other circuits to operate, I have personally never heard of it actually happening.

Kind Regards, John
 
Do other appliances work OK in that same socket? Does the microwave still trip the RCD if it's connected to a different socket, or a socket on a different circuit?
 
Yeah I though that too John, it could be that the current to trip is on the edge anyway and the microwave tip it over the edge. I suppose there could be a case for going round unplugging things to rule out a n-e fault elsewhere. If it's the initial surge then other high power appliances like kettle or hob/shower would also trip it.
OP does any trip happen if you turn on lots of high power appliances?
 
Yeah I though that too John, it could be that the current to trip is on the edge anyway and the microwave tip it over the edge. I suppose there could be a case for going round unplugging things to rule out a n-e fault elsewhere.
Nothing would be lost by trying that. However, my mind cannot stop focussing on the fact that, if everything is wired correctly, N-E faults really should not normally cause 'the other RCD' to trip. Bernard may well pop up with a diagram showing how it theoretically could happen - but, as I said, for what it's worth I have never personally heard of it actually happening.

Kind Regards, John
 
Have taken a look in the board. Everything looks fine.

Its def a case of it tripping the other rccb when switching on the tripped one
 
Its def a case of it tripping the other rccb when switching on the tripped one
As I've been saying to JohnD, that is something which, under normal circumstances, really should not happen - so it warrants investigation. After all, the whole point of having circuits split onto two RCDs is that a fault causing one RCD to trip should not have an effect on the other.

If I were you, I wouldn't 'write off' the microwave just yet, even though it's very likely that it is faulty (even if something else is 'wrong' as well).

Kind Regards, John
Edit: crucial missing word put in!
 
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