I'm installing a ducted extractor fan with run-on timer in my loft to give extra steam extraction for the bathroom. The bathroom has an opening window so I want the fan to be switched separately totally independent of the light (don't want to have to turn the light on if it's daylight, and don't want the fan to run unnecessarily every time you turn the light on). There will be no wiring in the bathroom itself as the fan is up in the loft and I want a wall switch outside the bathroom to turn it on/off.
I know about the fan needing a permanent live (3 core + earth from the junction box etc) but want to know if I can use a 3A fused double pole switch on the landing as a simple on/off switch. Thinking ahead when decorating the landing some months ago, I already chased out and installed a back box outside the bathroom and 2 core 1mm cable up into the loft, so want to keep this arrangement if possible. I keep reading about fans needing a fused isolator outside and then another pull switch inside the bathroom, but I just want to be able to turn the fan on/off as required from outside on the landing and have it run on a few minutes after I switch off.
The wiring diagrams supplied with the fan all assume you're linking it in with the pull cord light switch and I can't find any info on having the fan independent.
Fans do fail so you do need a means to isolated often a fused connection unit (FCU) although a double pole switch will isolate you need a means to lock off in case of a fault well maybe! The triple pole isolators do have little holes where a clamp and lock can be fitted.
The normal where window exists where as you rightly state the fan should not be part of the lighting circuit is either a pneumatic timed push button or a PIR. Although the simple switch will work it's common to forget to switch off. It would need a neon as the fan would still run on so any visitor would not know if on or off.
On thing I find a problem is getting air into the bath room to replace that pumped out. Do remember with any open flue appliances in the house negative air pressure can be dangerous. Balanced flues should be OK. I have a gas fire in my living room which in theory means I should not use a vented tumble drier I just don't use fire except for when there is a power failure.
Thanks for the info ericmark. I decided to fit a FCU next to the fan in the loft and use the switch on the landing as a simple on/off switch. Fan is quiet but can just about hear it running so we shouldn't forget to switch it off and will just tell any guests as and when.
Bathroom window is open almost all the time anyway so replacing extracted air isn't a problem. It's just not enough to get the steam out on its own.
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