How to isolate an earth leakage problem

[Justloadit]

TBH I'm not sure why it would cause an RCD to trip, there's no current imbalance on the load side which is the criteria for tripping. I'd guess it's an anomaly with the internal electronics maybe.

I think it has to do with reflected current flows in the E/N wires. All circuits connected to the council point on the E/N circuits are connected in parallel to all the different loads, however when there is a break on the council side supply line, as is the case described by ACEsterhuizen, and because of high current flows and inductance in these circuits, a pulse is injected into the neutral line towards the load side. THE RCD , by nature of its design, is to trip when there is an imbalance in the currents in the L and N circuits. When this pulse comes down the line, there is a mismatch between the L and N, and the RCD can not differentiate where the imbalance is coming from, source or load, and the mechanism then trips.