New FB RCCB tripping

[houstonwehaveaproblem]

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

 

[John D v2.0]

Broken microwave, maybe it has an insulation fault.
Were you microwaving something particularly steamy at the time? Baked potato or porridge or something?

 

[houstonwehaveaproblem]

No literally just as i push the start button!

 

[John D v2.0]

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.

 

[JohnW2]

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

 

[aesmith]

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?

 

[houstonwehaveaproblem]

Thanks guys.

Toaster is in same socket. No probs with that.

 

[John D v2.0]

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?

 

[JohnW2]

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

 

[houstonwehaveaproblem]

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

 

[houstonwehaveaproblem]

OP does any trip happen if you turn on lots of high power appliances?

Havent tried that yet

 

[JohnW2]

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!

 

[boringoldcodger]

Deleted, as no longer relevant.

 

[JohnW2]

Slightly pedantic time again, I believe John meant "shouldn't".

I did. Now corrected. Thanks.

Kind Regards, John

 

[houstonwehaveaproblem]

Ok...

The busbar wasnt cut so was joined between both RCCB’s