I'm looking at a 2.5 mm^2 ring main cable in a flat-roofed bungalow, mostly running in the ceiling space (about 8" deep under the top deck&roofing felt) and dropping down to sockets.
Looking at the installation method reference codes, I cannot see anything that quite matches: (a) a pair of cables touching side by side as they go down to a socket. Cables are a close fit inside steel capping running vertically, nailed to a thermalite block wall. Covered by dot&dab plasterboard - close to the capping but may have a slight gap.
(b) single cable (or two on different rings with >1 cable space between them) clipped along a joist about 50 mm above the ceiling. Insulation batts wedged between joists, an inch or so above the wire.
(Presume this is better than having the wire above the insulation as that zone gets very hot indeed in summer - the space below the insulation seems useful to prevent ceiling spots overheating).
(c) single cable passing through 25 mm holes in the joists to run along the room, insulation (100mm) resting on top of cable where it goes from one joist to the next; 4" of air space below.
(d) single cable running down in a plasterboard-covered cavity, clipped to cold brick wall on one side; cavity filled with 100 mm insulation behind plasterboard.
OK for a 32A MCB...or better with 25?
Joe