PeteZahut wrote:
Im looking at the possibility of buying an extractor fan with built in
spotlight like the ones used in bathrooms.
Secondly, the ones I have been looking at require 4 wires and an isolating
switch.
The four wires are one permanent live to enable the fan to run on when the
light goes off. One live, one neutral (switched live?) and one earth.

Live, switched live, neutral, earth.

I gather the isolating switch is to enable work to be carried out on the fan
if needed but how would this be done. Dont all isolating switches only have
three connection points?

Fan isolators have three poles (L, SL, N - the earth is *never* switched).

Is it just the permanent live which needs to be
fitted to this switch?

Assuming you don't want to use the timer facility, supply the fan with
Live and Neutral, and link the PermanentLive and SwitchedLive terminals
at the fan. If you are taking the supply from a socket circuit, use a
Fused Connection Unit fused at 3A.

Owain