Nightmare of a day. RCD tripiing under any load

[Richard Burns]

What's confusing me is why when I plug anything into kitchen socket covered by RCD A is it tripping RCD B? Surely this means it can't be a N to E fault as it would trip RCD B if this was the case

If you have an NE fault on a circuit on one RCD then loading a circuit on the other RCD can cause the first RCD to trip.
Did a diagram for you:

 

[wersolaruk]

You have a n-e fault, megger everything buddy! All fronts off etc, good luck with it mate!

 

[shockboy]

try lighting common fault landing light 2way neutral on upstairs circuit feed took from downstairs ciruit

 

[markythesparky]

Thanks for replies guys yes everything tested out ok. So we are looking at a borrowed neutral most likely then?

If its a borrowed neutral then how did it test out ok?

 

[bigspark17]

Borrowed neutral on light circuits.! Put all lights on same rcd and try.!

 

[trev]

Borrowed neutral on light circuits.! Put all lights on same rcd and try.!

Or check to see if there really is one, locate it and eliminate it.

 

[Engineer54]

Every time we get a thread about RCD's tripping after a CU change, the common consensus is either a N-E fault or a shared/borrowed neutral. And every single time the OP has failed to test the installation prior to replacing the old rewirable CU with one containing at least two RCD's.

How many more times do these guy's NEED to be told to test these installations before they start changing them out for god's sake??

What's more, why is this fault causing such a problem to find and rectify. I would have thought that in around an hour, an experienced electrician would have sorted this problem out, ...or at the very least well on his way to finishing off any remedial work...

 

[markc123]

Test before touch

:shame: that's where i've been going wrong.

Wondered where my afro had come from.

 

[brizospark]

Eng54 do you honestly think in the real world customers would give the go ahead to carry out testing before changing a board? This would mean an additional cost on top of a board change The customer would simply get someone else to do the job!

 

[trev]

A test for borrowed neutrals plus an IR plus an EFLI wouldn't take very long at all would it?
You've already done enough there to identify any major problems and you're doing the rest of the tests anyway on completion of the change so what's the problem?