Bathroom extractor fan electrics

iphone4

I currently have a basic pull cord operated extractor fan (Silavent SDF 100PB).
You have to manually pull cord to switch on (easy enough), but switching it off 20 minutes after using is very inconvenient (I've left for work by then...)

So, I want to upgrade to an automatic humidistat one, but can I avoid getting an electrician in? I've removed and replaced the existing one before so I'm happy replacing it with one that has the same wiring, but currently there are just two wires (switched live and neutral), and all the humidistat ones, tend to have a timer mode too and run require three wires (live, switched live, neutral).

What would happen if I wired the switched live to both live terminals, and left the pull core on all the time? Would the humidistat just switch on and off based on humidity level? Will anything bad happen?

The replacement will possibly be the X-Mart IPX4 Humidistat one.

keystone

I think you should get an electrician or buy a fan with a timer only that just needs switched live and neutral. Forget the humidistat part.

Cheers

Owain_Moneysaver

Live to both terminals may cause the fan to run continuously in timer mode. Try it with just the continuous live connected.

Strictly speaking you need an all-pole isolator switch on new installations.

"Part P" does not apply as this is a like for like replacement.

keystone

Owain_Moneysaver wrote: »

Strictly speaking you need an all-pole isolator switch on new installations.

Actually theres no "strictly speaking" about it if you don't mind me saying so. If he needs a new cable then he must have a two pole isolator outside the bathroom and the circuit must be RCD protected becaue it will have to be to the 17th and it will have to be notified under Part P. The simple solution is to fit a timed fan (forgetting the humidistat option) to the existing wiring and change nothing else.

"Part P" does not apply as this is a like for like replacement.

Indeed so but its a moot point as to whether he needs an MWC. I say he wouldn't. The clock is ticking.....

Cheers

iphone4

Thanks for suggestions. I'll try just connecting the continuous live. I don't mind about the timer behaviour as long as the humidistat switches it on and off when needed.

keystone - I don't understand your suggestion of a timer only fan. It's the timer that requires live and switched live (switched live to know when to start, and live to be able to continue after the pull cord is off). At least that is my understanding.

keystone

Sorry - having a brain f.rt tonight and talking b......ks .

Just ignore me.

Cheers

andyhop

You can purchase a expelair premier humidistat fan without timer, Still has a pullcord option if a boost is needed

iphone4

So does anyone have a fan with timer+humidistat. What happens if you leave them switched on all the time? Does it just come on when the humidity is high and switch off automatically?

keystone

Right brain in gear again.:o As Andyhop suggested buy one with a humidistat but without a timer. Xpelair do them in the DX range as well. The humidistat is effectively a switch anyway and the fan will then only operate when the humidistat tells it to. Am assuming that the fan electrics are independent of the lighting, of course.

Cheers

iphone4

Yes, current switch is pull cord separate from lighting.

The Xpelair DX100HP looks fine from a wiring point of view, but although it's described as a "100mm axial extract fan", it seems to require a 115mm hole in wall.

I currently have a 100mm hole in wall, and would prefer not to change that.

Garetha

iphone4 wrote: »

So does anyone have a fan with timer+humidistat. What happens if you leave them switched on all the time? Does it just come on when the humidity is high and switch off automatically?

Yes!
Ours runs at odd times briefly - we never switch it off.
Within seconds of starting a shower it starts up and runs until the humidity falls below its threshold.
It's a low voltage device with a mains to low voltage transformer near the mains supply.