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New bathroom extractor fan and light switch

Discussion in 'Electrics UK' started by gdunbar, 16 Jan 2017.

  1. gdunbar

    gdunbar

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    Hello,

    I'm going to have a Manrose MF100 inline extractor fan installed in the loft for our bathroom. The electrician suggested wiring up the fan from the bathroom light and installling a pull cord in the bathroom to switch the fan off and on, as we didn't want it switching on with the bathroom light. We already have a pull down cord for the light and i've now realised its going to look messy with two pull down cords in a small bathroom.

    I'm now thinking of removing the existing pull down cord for the bathroom light and having a double switch on the outside of the bathroom to control the light and fan.

    The fan also mentions it needs to be protected by a 3Amp fuse. The existing lights are on a 6Amp MCB & RCD.

    Do i also need to add a Fused Connection Unit for the fan? http://www.screwfix.com/p/13a-fused-connection-unit-spur-white/3524d

    Also i'm assuming I also need to add an isolator switch for the fan, which I was probably going to install above the outside of the bathroom door?

    Once i know what switches I need then I can install the back boxes in the plasterboard wall ready for the electrican to install the cabling.

    Thanks for any advice/suggestions.

    Glyn
     
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  3. flameport

    flameport

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    That's fine. Or put the switch in the bathroom if it can be at least 60cm from the bath/shower.

    If you want to do that, a 3A FCU will be required. That could also be used as the isolator.
    Electrically there is no reason for the 3A fuse, it's just something that some fan manufacturers put in the instructions for reasons known only to them.
     
  4. gdunbar

    gdunbar

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    Thanks flameport, if I do decide to install the 3A FCU i'm assuming it's perfectly ok to have it located next to the inline fan in the loft out of the way and then to have an isolator above the bathroom door.

    Thanks

    Glyn
     
  5. JohnD

    JohnD

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    Why not?
     
  6. JohnW2

    JohnW2

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    The OP will undoubtedly answer for himself, but there are two common reasons why people don't want a fan to be light-operated. Firstly, they don't want the noise of the fan if they make a brief visit to the loo in the middle of the night. Secondly, if there is a lot of natural light in the bathroom, they don't want to have to switch on the light to get the fan to come on during the day. I don't think either of those issue would bother me personally, but we often hear about one or the other.

    Kind Regards, John
     
  7. JohnD

    JohnD

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    It's a nice powerful fan, and amazingly quiet. When tucked away in the loft I was going to reassure the OP about the low noise.

    It takes a while to dry a bathroom, so I'm in favour of using the extractor a lot, without needing to make a conscious decision to turn it on.
     
  8. winston1

    winston1

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    That is rubbish about a 3 amp fuse. An external fuse is to protect the cable not the appliance, which should have built in protection. I'm sure the supplied cable will be rated at more than 3 amps. There is no need to follow the manufacturers instructions, especially when they are so clearly wrong.

    Note also that fused connection units are not used or required on lighting circuits.
     
  9. EFLImpudence

    EFLImpudence

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    Nearly all bathrooms (where no fundamental problem exists) dry naturally in a while.
     
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  11. bernardgreen

    bernardgreen

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    A motor can fail in a mode which takes far more current than it normal operating currrent. Without a 3 amp fuse in the fan supply that over current will take out the fuse / MCB for the lighting circuit and thus put all the lights out.

    When the fan is taking too much current ( fault or stalled rotor ) the 3 amp fuse will ( at least should ) blow before the 6 amp fuse / MCB protecting the lighting circuit and thus lights will still work.
     
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  12. JohnW2

    JohnW2

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    ... but one often can't avoid the need for a 'conscious decision'. If the fan is operated by a manual switch, then one has to make a 'conscious decision' to operate that switch. If the extractor is linked to the light then, per my second point above, one has to make a 'conscious decision' to turn on the lights (even if/when lights are not needed during daylight hours) in order for the extractor to operate.

    This obviously all depends upon whether the room has adequate natural lighting and whether one's use of the room is mainly doing daylight or night-time hours.

    Kind Regards, John
     
  13. JohnW2

    JohnW2

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    Whilst that is obviously qualitatively true, I have always seriously doubted that the stalled current drawn by a standard bathroom extractor fan (with a tiny motor) will ever be very much at all ...

    ... I've just tried with a standard 4-inch Manrose extractor fan (specified as "20W"). Running normally with a supply of about 240V it draws 90.5 mA (i.e. about 21.7W at 240wV). With the rotor jammed, the current rises just slightly to 105.2 mA. Perhaps even less rise than I had expected, but certainly very little.
    That's all very well but, if the fan I've just tested is anything like typical, a stalled current of about 0.1A is obviously not going to blow any fuse, or trip any MCB!

    An actual L-N 'short' within the fan obviously would (as it would within any equipment) result in a fuse and/or MCB operating (no telling which, or both), but the fan motor stalling is (as I suspected) clearly not an event that would ever cause any OPD to operate, and is certainly not a reason for having the infamous 3A fuse!

    Kind Regards, John
    Edit: typo corrected
     
    Last edited: 16 Jan 2017
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  14. omega015

    omega015

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    Don't regs state about following manufacturers installation instructions? I use the click mini-grid switches that allow fuses, fan isolator and switches etc.. in one faceplate. Also depending on the installation you might need two fuses (for live and switched live) to satisfy the manufacturers instructions.
     
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  15. JohnW2

    JohnW2

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    No longer - since Amd 3 appeared in 2014, one merely has to "take account of" the MIs, which means that if one is confident, one can apply discretion and/or common sense.
    As above, if your personal professional judgement is that a fuse (and/or "3-pole isolator") is not required (and are prepared to justify that judgement) then you are no longer required to blindly obey MIs. ... and the experiment I've just done confirms the belief I've always had that there is no electrical reason for needing a 3A fuse (on a 6A lighting cct).

    Kind Regards, John
     
  16. omega015

    omega015

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    Thanks John, it was about 4 years ago when I can across this little issue on one fan. Glad common sense has prevailed on this one, although some DIY'ers common sense will lack far short of this.
     
  17. JohnW2

    JohnW2

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    Indeed, and it obviously applies much more widely than just to fan isolators and fuses. You probably saw the recent discussion about "panel heaters" etc. Despite 'common practice" there is clearly no electrical reason why a 2kW one is fine with a 13A plug, but a 2kW wall-mounted one "must" be hard-wired (as many/most MIs say) - so, again, one can now apply common sense if one is confident and comfortable so to do!

    Kind Regards, John
     
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