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Extractor fan with fused isolator

Discussion in 'Electrics UK' started by mjas, 23 May 2019.

  1. mjas

    mjas

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    I have just bought a replacement bathroom extractor and also a 3 pole fused fan isolator switch since the old fan wasn't installed with an isolator and the fan manufacturer recommended a fused switch.
    I have a question about the wiring between the fuse and the switch. Can I use a section of single insulated wire stripped from a piece of 3 pole cable to connect my fuse out into the (permanent) live of the switch i.e. a bit like the attached image or is there another way to do it? Also, does it matter if the fuse is wired before or after the switch?
    Thanks
    Switch.jpg
     
  2. JohnD

    JohnD

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    Is your fan going to be supplied from a lighting circuit, or from a socket circuit?

    What is the fuse or MCB rating for the circuit that will supply it.

    BTW I can't see how a single fuse in your switch will protect both a switched live and a permanent live. It would be interesting to see the instructions.
     
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  3. donrkebab

    donrkebab

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    Fuse should be after the switch, so your link is in the wrong place, connect as follows;
    Permanent live into top L1
    Link bottom L1 into Lin
    Live out into Lout.
     
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  4. mjas

    mjas

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    Thanks for the speedy replies.
    John D
    The fan is on the lighting circuit which is on a 10A fuse.
    The instructions said " a double pole fused spur having contact separation of a least 3mm in all poles must be used and fitted with a 3A fuse "
    The single switch I got was to avoid having to get a 3 pole isolator and a separate double pole fused switch.
     
    Last edited: 23 May 2019
  5. JohnD

    JohnD

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    10A?

    are you in a commercial building?

    Does your new fan incorporate a timer?

    Are you planning to instal it so it continues running for a period after the light is turned out?
     
  6. EFLImpudence

    EFLImpudence

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    That's a very peculiar switch.
     
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  7. JohnW2

    JohnW2

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    I think it's a standard 3-pole Click module. What do you think is peculiar about it - or do you perhaps just mean that it is not something we commonly see (with which I would agree)?

    As always, if this is (as one assumes - given the reference to a 3-pole isolator) a timer fan, if one wants to obey manufacturer's 'requirements' for a 3A fuse, it is not straightforward for a single fuse to protect both permanent and switched live.

    Having said that, the reality is that, even if one feels that the permanent live should be fused, there is not much of a rational reason for fusing the switched live, since that is just a 'trigger' input, invariably connected to the timer circuitry via a very high value resistor - so is extremely unlikely to ever carry significant current (which could only happen if that resistor somehow failed s/c or got bypassed).

    Kind Regards, John
     
  8. mjas

    mjas

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    The fuse in my fuse box says 10 on it so I assume it is 10A (the others say 16 or 32). It is a domestic building.

    Yes the fan has a timer and the intention was for it to switch on with the light and run for a period after the light is switched off. The existing fan did that but was not fitted with a isolator which I believe is against current regulations.

    The switch is this one. https://www.qvsdirect.com/excel-3-pole-fused-fan-isolator-switch-white

    Fuse.jpg
     
  9. EFLImpudence

    EFLImpudence

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    Well that is what peculiar means.

    It is a grid switch so why sell it like that - ready made? It has confused the OP.
    If thought useful to have a three-pole switch with the fuse on one pole, so why not make one?

    Except the switched live will still be live when the fuse has blown.
     
  10. mjas

    mjas

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    It may be an unusual switch but as far as I can see it does allow me to fuse the permanent live as required by the manufacturer and isolate the fan as required by regulations. Good point that it could have been constructed in a more user friendly manner though.
     
  11. EFLImpudence

    EFLImpudence

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    Do the instructions not require a fuse for the switched live as well?

    There is no regulation stating that a local isolator is required, nor a fuse for that matter.
     
  12. JohnW2

    JohnW2

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    Well, given that manufacturers appear to persist in asking for both those things, there presumably would be an appreciable market - but, despite that, I don't think anyone offers such a product, do they? I didn't realise that Click sold a 'ready made' unit such as we are looking at, but I presume that are offering it to emulate that 'dedicated' product that does not seem to exist.
    Yes, that's true and the same problem would exist if one separately fused the L and S/L (since the latter would virtually never blow, even if the former did). One would hope that, since it was there, people would use the (3-pole) isolator for it's intended purpose before 'touching anything' - but nothing is certain!

    I think that means that the only way one could satisfy the manufacturer's requirements whilst also avoiding the issue you mention would be to put the 3A fuse in the feed to the light/switch - which would inevitably mean some change to the existing wiring of the light.

    Kind Regards, John
     
  13. mjas

    mjas

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    All the instructions say is a double pole fused spur although further in the detail it says an omnipolar switch. It also says the circuit must be protected by a 3A fuse.
     
  14. bernardgreen

    bernardgreen

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    It is not rocket science.

    If timer over run is required after the lamp is turned off then the isolator cannot be used to control the light

    To have timer over run requires one switch and one isolator.
    .


    0x92.jpg
     
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  15. EFLImpudence

    EFLImpudence

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    Exactly. Is there not a diagram in the instructions similar to Bernard's?
     
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