Hi, I am trying to fit a bathroom fan with a humidistat to replace an old, failed switched fan. There is only a 3 core cable (so live, neutral and ground - no switched live) There is an isolater switch outside the bathroom. I don't mind the fan being enabled all the time, switch off only by the isolator if the need arises. See the wiring diagrams attached. What I don't understand is how the unit detects the LS and L being bridged. Surely, when LS is live (because a light is on), it is equal to live? So LS and L being bridged is the same as having a LS switched to on? Bridging LS and L definately does disable the humidstat and timer - the fan just runs I think leaving LS disconnected does achieve what I want, but it might mean that leaving LS floating actually means the fan will turn on randomly? (I can't re-wire and run a cable with live-switched -- there is a floor above the room and I cannot access the wiring without removing all the flooring etc) Any insights would be appreciated!
The fan needs a switched live to activate the timer humidistat circuit, without that I don’t believe it will ever start.
Just leave LS un-connected. In normal use it will have several metres of cable running to it which will be "floating" and nothing ever happens even when that pick up stray voltages. It may well be designed with a high value (200k) resistor to pull it down.