Changing a mains fed extractor fan in a bathroom for a SELV

[webde]

I want to replace an existing mains operated extractor fan over the bath with a SELV fan. I realise that the wiring must ultimately be done by a registered electrician so I can get a proper certificate for the work, but I first want to establish what are the legal requirements as opposed to those which are just desirable.

Firstly, the consumer unit is the old fuse box type and in particular does not incorporate a RCD. If I change the electrics in the bathroom such that the existing wiring for the mains fed fan goes instead to a transformer outside the bathroom, will I have to have the existing consumer unit changed too?

Secondly, the manufacturer says that the supply to the pullcord switch should be a double pole fused spur. Is this essential? If so, would it be acceptable to instead place the fused switch (or possibly two) immediately before the input to the transformer?