Wiring a Bathroom Extractor Fan with an Isolator Switch.

Discussion in 'Electricians' Talk' started by glob@l, Jun 13, 2019.

  1. glob@l

    glob@l Active Member

    The bathroom lights are operated from a pull switch, the isolator switch is adjacent to the pull switch on the corridor side of a stud partition. Three core and earth has been run from the pull switch to the extractor fan. In straight forward terms how are the three parts wired.
     
  2. Comlec

    Comlec Well-Known Member

  3. glob@l

    glob@l Active Member

    Thanks!
    Is that the London underground map?
    As it stands, I believe the feed is at the switch, so if I understand the above image correctly the feed goes to a lamp/light then to the switch and isolator and onto the extractor? Is that the only way it can be done? If that is the case it would need rewiring? Incidentally the extractor will have a run on function if that makes any difference.
     
  4. unphased

    unphased Screwfix Select

    If the feed is at the pull-cord switch, loop a live in to the isolator off the switch, loop a switched live in to the isolator off the switch and a neutral off your light fitting to the isolator. As long as you have a live, switched live and neutral going to your isolator first, the rest is simple to feed to the fan, all as above diagram. The live feed ensures the run-on timer operates.
     
  5. robertpstubbs

    robertpstubbs Well-Known Member

    It’s a simplified version of the map with the CPCs/earths left out.
     
  6. glob@l

    glob@l Active Member

    Thanks for the feedback!
    Presumably by loop you mean individual wires of the appropriate colours. This may be obvious to others but why is the neutral looped from a (3 X spots)) light fitting? To clarify, is three core and earth suitable for feed to the fan? I notice the earth has not been mentioned or shown in the above diagram, so am I right to say it's not necessary?
     
  7. Bazza

    Bazza Well-Known Member

    Of course earths are necessary. They must be provided at every point in the circuit, even if the device doesnt itself need an earth (fan in your case). So yes, 3-core and earth foor the connection from the isolator to the fan, also the cable from the ceiling junction to the isolator.
     
  8. glob@l

    glob@l Active Member

    By 'ceiling junction' do you mean a spot light, the switch or both for 3 core and earth connections/loops to the isolator? Your wording regarding the earth wire is exactly what I meant, I should have said 'not needed' instead of not necessary.

    I can't think why the neutral loop comes from a light?
     
  9. robertpstubbs

    robertpstubbs Well-Known Member

    To clarify, when I mentioned above about the earths being left out I wasn’t recommending not using them, but simply replying to the OP’s implication that the wiring diagram was as complicated as the Underground and suggesting it would look even worse if the earths were included.

    I could argue with you all about the necessity of earths in various situations, but where 2+E and 3+E are used, then the earth cable should be connected to the earth terminals for 2 reasons even if sometimes it may seem pointless.

    Firstly some sparks aren’t too bright and they need somewhere easy to connect every wire, or their minds will blow.

    Secondly leaving an earth wire loose would allow the possibility of it coming into contact with a live or neutral.
     
  10. glob@l

    glob@l Active Member


    Surely the neutral wire can be looped from the pull switch like the other wires?
     
    Last edited: Jun 27, 2019
  11. unphased

    unphased Screwfix Select

    Yes if there is a neutral wire at the switch. Quite often there isn't, that's why I said to do it the way I said. :)
     
  12. glob@l

    glob@l Active Member

    I'm with you now, thanks for clearing that up.
     
  13. glob@l

    glob@l Active Member

    As described above, I connected the fan through the fan isolator switch to the pull cord with 1mm three core and earth cable.

    The existing wiring at the pull cord was a bit untidy, so I decided to tidy it up a bit and make it easier to work on. All four neutral wires ( 3 black, 1 grey) are connected through a block connector, and all four earth wires are also connected through a seperate block connector.
    That leaves three red (old colour) and one brown (new colour) wire, I believe these should be connected to L2, as permenant live and one black (new colour) wire, which I believe should be connected to L1, as switched live?
    However the existing pull cord I have does not have an insert or screw at L2 to secure wires with? I'm not sure if they were there before I started, or not?
    The only other terminals are com and what appears to be a symbol with a number of horizontal deminishing lines with one vartical line above, or otherwise, depending on how you look at it?
    Please advise if the above is correct or otherwise.
     
  14. glob@l

    glob@l Active Member

    Job done, thanks all!

    I have a second fan isolator switch to fit to an existing fan, operated from a pull switch, Will this one have to be rewired from the fan to the pull cord via the isolator switch , or can it be wired from the pull cord?
     
  15. Bazza

    Bazza Well-Known Member

    y
    Does the light switch have a neutral? Most do not.
     
  16. glob@l

    glob@l Active Member

    It does have a neutral connection.
     
  17. Bazza

    Bazza Well-Known Member

    Then, you’ll need 3-core & earth cable from the light switch to the fan isolator, and then more 3-core & earth cable to the fan.
     
  18. glob@l

    glob@l Active Member

    From the description above, would there have been any need for the electrician to instal the fan with 3 core and earth or would 2 core and earth have been adiquate? The latter?
     
  19. Bazza

    Bazza Well-Known Member

    If you have a timer fan, it needs
    Live
    Neutral
    Switched live
    And earth

    You can’t do it with 2 wires.
     
  20. glob@l

    glob@l Active Member

    Ah! right, it does have a timer, therefore the existing cable must be 3 core and earth, as you say. With a bit of luck there will be loose cable in the ceiling void, enough to span to the other side of a stud partition. Then it's just a case of connecting to the pull switch with the same cable. Thanks.
     

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