Dave Plowman wrote in message ...

Assuming it's carrying mains, what do the regs say about treating
flex as permanent wiring in terms of long runs within a house?

Use of flexible cables and cords is not ruled out provided all the usual
relevant requirements are met [521-01-04]. IMO though, it's inappropriate
for normal fixed power & lighting wiring where more suitable cables are
readily available. For multi-core control wiring (like CH controls) it's
quite OK.

Minimum (copper) conductor sizes for all types of cable are defined [Table
52C]:

- 1.0 mm^2 for power & lighting circuits

- 0.5 mm^2 for signalling & control circuits

- 0.1 mm^2 for signalling & control cables with 7 or more conductors
intended for electronic equipment.

(All conductors must be adequately protected against overheating caused by
fault (s/c), and where relevant, overload current.)

When using multi-core cables, colour coding must be observed [Table 51B]:

- 1, 2, or 3-core cables to use the usual brown, blue, green/yellow

- 4 or 5 core cables may use either brown or black for phase (live)
(5 cores is not mentioned, but I'd assume the same)

- cables including plain yellow or green cores are not allowed

- cables including any bi-colour combination other than grn/ylw are
not allowed.

--
Andy