In article ,
Vass writes

Thanks Fred
I was wrong, I have 10mm and the Shower is 10.5kW
I have opted for a switch to be situated outside the bathroom
that way the cable will run straight up from the garage to the airing
cupboard
which is next to the bathroom and where the back wall of the shower is
so becomes simple.
proposing then
10.5kW shower
10mm cable
45w switch
40 trip switch on RCD'd CU

Ok, 10mm2 is fine unless it's passing through insulation, move it (cable or
ins) if it is. Real world load (the uk is really 240V, not yet 230V) is just shy
of 44A so switch is fine but breaker is a bit light. At 10% overload it won't
burst into flames and probably will never trip but an upgrade to 45A might
be something to add to the to-do list.
--
fred
Plusnet - I hope you like vanilla