External garage electricity wrongly connected to neighbours supply

[EFLImpudence]

It is right Part of the N current from a load protected by a different RCD goes 'backwards' through the N side of the RCD protecting the circuit with a N-E fault, thereby creating an L/N imbalance (hence a trip, if enough imbalance) of that RCD ...



No. The full N current from load (as well as the full L current from the load) goes through the RCD protecting the circuit(s) with a load ("RCD1" in diagram above), hence no trip of that/those RCD(s)

Yes, I obviously misread your post. I thought you were saying both RCDs would trip.

This is the situation in Bernard's frequently posted diagram .

 

[JohnW2]

Yes, I obviously misread your post.

Fair enough.

I thought you were saying both RCDs would trip.

As you now realise, I obviously wasn't saying that.

The important point is that many people don't seem to realise that a load protected by a different RCD can result in tripping of an RCD protecting a circuit with an N-E fault - and, even if they do realise that, don't also realise that, if it happens, the RCD protecting the load (but not the circuit with the fault) will not trip.