I'm replacing the lighting spur in my kitchen as part of a bigger renovation (Scotland, building warrant, etc). The current (boom! boom!) wiring is twin conductor in steel conduit. I don't know how old this is but the insulation on the wire seems like plastic rather than rubber so I guess it was replaced at some point in the not too distant past.
The supply for each light ruins trough the switch, rather than a switched live back from the rose, so I need to replace it. Building regs require a mains powered smoke alarm (run of the lighting circuit) so I need a permanent live to the rose.
Anyway, I'm not keen on a total rewire back to the CU (the conduit is quite narrow and pulling twin/earth all the way through might be problematic) and so wondered about terminating the conduit in a new junction box where it enters the room (Under the floorboards) and rewiring from there. I can't see any obvious problems with this so long as I get a good earth from the new junction box onto the exisiting conduit.
Any comments, am I missing something obvious, is this kind of "mixed mode" wiring acceptable in the 21st centrury?
Thanks