Bathroom extractor fan electrics

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iphone4
iphone4 Posts: 10 Forumite
in In my home (includes DIY) MoneySaving
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.
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  • keystone
    keystone Posts: 10,916 Forumite
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    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
    The difference between genius and stupidity is that genius has it's limits. - Einstein
  • Owain_Moneysaver
    Owain_Moneysaver Posts: 11,360 Forumite
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    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.
    A kind word lasts a minute, a skelped erse is sair for a day.
  • keystone
    keystone Posts: 10,916 Forumite
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    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
    The difference between genius and stupidity is that genius has it's limits. - Einstein
  • iphone4
    iphone4 Posts: 10 Forumite
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    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
    keystone Posts: 10,916 Forumite
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    Sorry - having a brain f.rt tonight and talking b......ks :D.

    Just ignore me.

    Cheers
    The difference between genius and stupidity is that genius has it's limits. - Einstein
  • andyhop
    andyhop Posts: 1,996 Forumite
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    You can purchase a expelair premier humidistat fan without timer, Still has a pullcord option if a boost is needed
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  • iphone4
    iphone4 Posts: 10 Forumite
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    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
    keystone Posts: 10,916 Forumite
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    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
    The difference between genius and stupidity is that genius has it's limits. - Einstein
  • iphone4
    iphone4 Posts: 10 Forumite
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    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
    Garetha Posts: 981 Forumite
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    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.
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