On 26/01/2019 09:22, Chris Green wrote:
Is it acceptaple to run cables in (probably standard plastic clip on
cover) conduit fixed to the underside of exposed joists? I can't see
any reason why it shouldn't be OK but want to check.

It's to run a couple of 2.5sq mm feeds across the ceiling of a garage
which has a room above it but where the joists are exposed. Going
round the edge at the top of the walls is possible but rather messier
with obstructions and such (and would also use more cable).

You could just clip the cable straight across the underside, and then
use the metal normally used to protect cables under plaster in protected
zones "over" (or rather under?) it, if you see what I mean?. Also a
little bit mechanically stronger in the event of accidentally swinging a
tool between the joists.