On Mon, 17 May 2004 21:10:24 +0000 (UTC), in uk.d-i-y
strung together this:

The cables will not be grouped together at any point other than passing
through the joist - they will be side by side when going up the wall.

Well, if cables are briefly grouped, e.g. running through joists then
no, grouping doesn't apply. In a domestic situation though,
calculations are generally not required as 2.5mm is well in for
sockets, as is 1.5mm for lighting etc... are you overthinking a job
there?
--

SJW
A.C.S. Ltd.