Derek Doormer wrote:
Hi,
Just about to re-wire the lighting circuit, with the Loop-in system, the
cable from switch to light has the live switch (which I know is the black
which usually has red tape attached) but ive also read of people using
another colour (Yellow and Blue I think) and Ive also noticed Twin Red core.
So whats the best combination to use??

Whatever you've got a 100m reel of. Most frequent is using the very same
cable throughout the lighting circuit: so, red-n-black in the "old"
style, brown-n-blue in the Modern colours. Best thing to identify the
switched-live with is a bit of red or brown (old/new) sleeving, rather
than tape - tape falls off, while sleeving stays on being trapped
between the sheath and the connection. Twin red's OK (some pedants would
argue it's "best"), but has the practical issue of needing testing to
identify which core's which (or swapping the two wires round which you
find your switch is "down" for "off"). The yellow-blue thing you're
thinking of is 3core+E - yellow, blue, red in the Olde colours, brown,
black, and grey in the New one - most often used domestically for 2- or
3-way switching, or for running both a permanent and a switched live to
e.g. a bathroom fan: not the best of things to wire simple 1-way switch
drops with.

......................................... I've also read that 1mm or 1.5mm
cable is used, is it common practice to use 1.5mm for the circuit cable and
1mm for the switching cable?

No, again it's most simple to use the same cabling throughout. While
1mmsq is "nearly always" OK, 1.5mmsq has better "headroom" when it runs
buried in or under insulation - as it often will in th'loft. The
difference in cost is usually two thirds of sod all, so if you're buying
fresh I'd go with the 1.5.

Stefek