In article .com,
"Martin Pentreath" writes:
I have an old Wylex consumer unit, like this:
http://www.tlc-direct.co.uk/Products/WY804.html

I've bought an 9.5kW electric shower, but I've just discovered that
Wylex don't make 45A MCBs for these consumer units anymore, the highest
rated they produce is 40A. At 230v, 9.5kW draws 41.3A. Will I get away
with a 40A MCB or will it be forever tripping? (I have 10mm cable, by
the way, so 40A won't be a problem there).

The reason is most likely that the fusebox is only rated 60A in
total, and you may find your main fuse is also 60A in that case.
Sounds like you need to check if your existing supply can
support the additional 9.5kW load you are intending to add.
You may need the supply (or at least the main fuse) upgrading
to 100A and a new fusebox.

--
Andrew Gabriel