I don't see any issues. Technically, with round conduit you would apply a
grouping factor for 2 circuits in one tube - but as 16x32 is likely to
leave the cables apart, each one should suffer less as it will
effectively have its own bit of conduit/plaster surface to lose heat
through and it's the heating/cooling that rates the current carrying
capacity of a cable.


good point, the gap required for spaced circuits is something like 1
cable thickness?

so two 2.5 T&E in 32mm ducting taped to top and bottom of the duct
pretty much eliminates any grouping effects for the entire run in any
case?

the way I see it I'm unlikely to have any problems in any case, but if
I use some black nasty tape in a couple of places to ensure the two
cables are well separated I can make sure of it. no doubt that will
help with my "peace of mind"...