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Thread: Running extractor fan off a dimmer switch?

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    Running extractor fan off a dimmer switch?

    Hi there,

    I redoing my bathroom at the mo. I'll be replacing the GU10 halogen spots with dimmable LED equivalents. At the moment there is a plain old light switch that operates the lights and the bathroom extractor fan.

    If I replace this with a dimmer switch (trailing edge) would this ruin the relationship with the extractor fan? Obviously I don't want the fans speed to reduce with the lights! Wasn't sure if the switch just acts as a trigger for the extractor, which would then typically be powered off another circuit...

    Any hints would be most appreciated.

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    Re: Running extractor fan off a dimmer switch?

    Bumpity

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    Not a good person scaryjim's Avatar
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    Re: Running extractor fan off a dimmer switch?

    tbh I think you need to get a proper electrician on the job. Most light-switch operated extractor fans continue running after the lights are turned off, which suggests that the light switch activate a relay and the fan is on a separate spur (if it ran directly from the lighting circuit you'd expect it to cut out when the lights were turned off). OTOH, whether using a dimmer will fail to trigger that relay will depend on its properties, and I think that's where you need to get someone who actually knows what they're doing to look at it - otherwise you're just guesing and hoping, and that's a BAD IDEA (TM) when it comes to eletricity.

    I'm pretty DIY competent but there's a couple of things I won't touch, and electricity in a bathroom is right up near the top of the list. If you don't know any electricians ask one to come round for a quote and watch his face when you suggest swapping the light switch for a dimmer - it'll probably give you a good idea of what kind of job it is

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    Re: Running extractor fan off a dimmer switch?

    Quote Originally Posted by scaryjim View Post
    tbh I think you need to get a proper electrician on the job. Most light-switch operated extractor fans continue running after the lights are turned off, which suggests that the light switch activate a relay and the fan is on a separate spur (if it ran directly from the lighting circuit you'd expect it to cut out when the lights were turned off). OTOH, whether using a dimmer will fail to trigger that relay will depend on its properties, and I think that's where you need to get someone who actually knows what they're doing to look at it - otherwise you're just guesing and hoping, and that's a BAD IDEA (TM) when it comes to eletricity.

    I'm pretty DIY competent but there's a couple of things I won't touch, and electricity in a bathroom is right up near the top of the list. If you don't know any electricians ask one to come round for a quote and watch his face when you suggest swapping the light switch for a dimmer - it'll probably give you a good idea of what kind of job it is
    Generally, you run two live feeds to a bathroom fan. One from the permanent live, unswitched, side of a lightswitch. That power the fan. The other from the switched side, that triggers the 'on' moment, and starts the timer when turned 'off'.

    PS. I'm NOT an electrician. I've wired these things myself in the past, but I DO NOT give advice on things with a potential for lethal mistakes. Or rather, only one piece of advice .... as Jim said, if you don't know what you're doing, don't even try to to it. Get someone in that does.

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    DILLIGAF GoNz0's Avatar
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    Re: Running extractor fan off a dimmer switch?

    you should be fine but you must be outside of zone 2.

    http://www.buy-electrical.co.uk/cont...ing_zones.html

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    off a horse and helping your uncle jack off a horse.

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