In article . com,
puffernutter wrote:

Last night I turned off Consumer Unit 2 at the isolator and we
suffered a trip at about 02:30. Therefore there is nothing on
those circuits that can contribute to the trip. (Apart from the
tails from the "whole house" RCD to the consumer unit). Tonight
I plan to turn off consumer unit 1. I am hoping for a trip as
that will rule out my house wiring as a cause.

Think about a Neutral-Earth short, somewhere in the
house, either permanent or intermittant. It could
be in the cabling or in an appliance.

A permanent short could do nothing for most of the
time because your Neutral-Earth voltage is too low
to generate the required trip current (through the
resistance of your earthing rod, back to the supply
transformer). But the N-E voltage may then rise at
odd times, due to something happening externally.

An intermittant short (especially at 02:30) suggests
maybe the fridge. This is what happened here, with
the fridge (sometimes) doing an N-E short as it
turned off.

--
Tony Williams.