[quote author=yoda  link=1110912569/0#0 date=1110912569]Does a low voltage extractor fan need a isolator or can it just be run off the lighting circuit. [/quote]

If you ever need to work on it the light can be handy. Although there is no specific regulation, most sparks would feed it from the lighting circuit via triple-pole isolator - they make them especially for fans. (Three poles for live, switched-live and neutral - if it's not on a timer then you only need a double-pole jobbie)