Because the cable is obviously not 100% straight, it touches both of
the walls at various points.. Could this be a source of damp?

I will be putting some insulation into the cavity, but should be doing
anything else to protect the cables?

You may well find it bridges the cavity. It is usually better to chase the
inside wall and plaster over. If you must run in there, you should use cable
clips to fix to the inner (dry) leaf. The bricks are over 50mm wide, so you
can run the cable at any height. I'd suggest near the top where you can
swing the hammer for the clips. You must derate the cable for the expected
insulation, which may require a ring main to be run in 4mm (or even 6mm in
some cases) after the calculations.


AIUI, 2.5mm cable run in contact a conductive surface with the rest of
the cable completely surrounded by insulation is rated at 21A which is
sufficient for a 32A MCB protected ring main. This is all in the OSG
and was discussed here fairly recently (don't have the OSG to hand so
can't look up the table number for you). The only other thing you
*might* have to take into account is the total length of the circuit,
but that is very rarely a problem in a "normal" house!

I was originally going to run the circuit as a 'radial spur'. As I
have 4 double sockets, I was going to install a 13A fuse spur off the
existing ring and then just run a radial circuit from the spur to the
sockets.

But, considering that I want to put a 3kW heater in, the conservatory,
then thats 12.5A already..

So I decided on a ring.. I do have a fairly large house, and extending
it through the conservatory has added an extra 20m to this (10 meters
each way), so I hope that this won't be a problem!