6A RCD random operation. No obvious root cause.

[Simples]

PROBLEM SOLVED!!!

Inspection plan came up trumps. Starting from the room that seemed most suspect (Removing low energy lamp from ceiling pendant in that room reduced number of phantom RCD operations) I first removed the light switch. (RCD OFF of course). Carefully inspected the live and switch live conductors. Found the Switch live conductor insulation was slightly damaged on the outside edge of a bend, generated when pushing cable back into metal backbox. All my back boxes are of course earth bonded.
I therefore protected the damaged area with some insulation tape and carefully re-assembled switch plate back to wall. Then checked ceiling rose, all terminal screws secure and finally removed the top of the pendant holder. there was what looked like a fluffy spiders web bridging the terminals so I cleaned it all off.

As of now, lights have been on all evening (All lights upstairs to apply maximum current load) and no phantom trips.

Thank you to everyone who took the time and effort to reply.

 

[ColJack]

so we now need to add "spiders web" to our list of "things that can cause seemingly random RCD trips".. ( might be a good idea for a wiki article.. list of possible causes and how to eliminate them. )

 

[echoes]

Great!