On 14/02/2019 11:15, John Rumm wrote:
On 13/02/2019 12:18, wrote:

A situation that I can't found an answer to ...
There is a DP isolator before the main CU (which has an isolator).
This CU will be fitted with a 50A MCB feeding a 20m sub-main to a
second CU elsewhere in the house. There are therefore 3 ways to
isolate the sub-main.
Is there a requirement for the second CU (at the end of the sub-main)
to have an integral isolator switch?

If its a CU and not a distribution board, then you will need a main
I thought that, in a domestic situation, the terms "distribution board"
and "CU" were interchangeable ...
switch. There are two main reasons that spring to mind:

1) Expectation - from a user's PoV they expect there to be a main switch
present. A guest / future owner etc will not have the background
knowledge to know its a sub CU fed from another, and might be looking
for a way of killing the power in an emergency.
It's quite a large house and the main DP isolator (after the meter) will
be both more easily accessed than this sub-board and will isolate the
whole electrical system, rather than just the one segment.

2) Practical, you need some way to terminate the live of your incoming
sub main on the the live bus bar(s) of the CU. The live bus bar has no
terminals of its own, and relies on those of the main switch to connect
the incoming feed to the bus bar.
I'd planned to terminate the cable in crimped tags, bolted onto the busbar.

It's only a question of spec'ing a slightly larger CU (12 way rather
than 10 way) so I'll keep an isolator. Thanks, as always, for taking the
time.

The next question is which manufacturer: Hager, MK, BG, Wylex ... ? At
the moment I'm leaning towards Hager or MK because of space for RCBOs
and ease of getting parts.
Are there any good deals out there?