Christopher Key wrote:

I'm also concerned about nuisance tripping of this master RCD. Is a 100mA time delay RCD reasonably immune
from tripping under circumstances where there really isn't a problem?

We have an extensive electrical system (two large split load CUs)
protected overall by a single 100mA time delayed RCD. So far (in two
or three years) the time delayed RCD has never tripped.

The system comprises:-
Large house (6 bedrooms) with its own CU
'Outdoor' CU which supplies:-
Garage and games room, power and lighting
A second garage/workshop, power and lighting
Garden power for pond pump etc.
Small stable block, lights etc.
Outdoor lights

So I think my answer is - you shouldn't have a problem with nuisance
trips.

--
Chris Green