My TNC-S supply enters in the attached garage, where the tails are split
to a CU (in the garage, feeding: the kitchen, cooker, utility and a few
other bits) and a 60A switched fuse which feeds a 16mm2 sub-main.
The sub-main is about 20m long and connects to an ancient fuse board
that supplies the house radial and ring outlets. A second fuse board in
the same location is connected to one of the MCBs in the CU via a 2.5mm2
cable and supplies power to most of the house lights.
My plan *has* been to fit a new CU close to the garage and extend all
the cables back to it, but that requires a lot of disruption. I'm now
wondering whether I should simply replace the two wylex boards with a
single new (RCBO) CU in their present position and feed it from the
sub-main.
From some quick checks the existing 16mm2 will be OK at 20m for volts
drop if I protect it with a 50A MCB. However, from a quick look (more
poking around required) the only earth connection seems to be the CPC in
the 16mm2 T&E so that will need improving and the disruption involved
won't be much less than extending all the circuits, although it will be
less work.
What do the relevant panel experts think?