ARW wrote:

But as the OP has given no usefull info about the setup there is little
point in helping him.

FFS he spent more time giving info about the 5 flats that did work and and
the choice of CU than explaining the problem

Or a troll - he's been very quiet. Most people posting a question like that
would be on the net in short order looking for replies.

A real sparky, even a 4 day wonder[1], would probably have said they'd
tested the wiring and RCD (but probably without the appliances) and found
nothing wrong hence genuine confusion.

[1] On my 4-day-wonder course, the blatantly clueless and dangerous seemed
to leave after a couple of days. Everyone left could run the prescribed
tests and locate faults blind based on the tests.


--
Tim Watts