Mysterious 4th Wire

Discussion in 'Electricians' Talk' started by Suffolk, Sep 10, 2019.

  1. Suffolk

    Suffolk Member

    My sons house has a very old "Globe Lantern" outside his front door (part No LBLP 098)
    Today I went to replace it, with a more modern lamp
    Taking of the old fixture I noticed I had four connections
    Live/Neutral/Earth and a mysterious grey wire
    None of the wires had 240v, even with the light switch operated from indoors
    Is this this sensor wire ?
    Two questions
    (a)Where does it go indoors
    (b How can I bypass this wire, so that it can be single pole switch operated from indoors?

    Baffled, so any advice appreciated
     
  2. terrymac

    terrymac Well-Known Member

    You need to trace the other end of the cable. Can't be done remotely from a forum.
    You stated there is not 24Ov present at any conductors with " the light switch on ".
    Did the old light ever work / come on when said switch was used ?
    What test instrument was used to establish voltage ?
    Can you post pics here of cables at light AND switch positions ?
    Is there a remote motion sensor connected to this or any other outside light fitting ?
     
  3. Suffolk

    Suffolk Member

    Thanks for coming back
    The light has been intermittent over several months then totally failed
    I used multimeter to check between all wires
    Cannot supply pic now back home 10 miles away
    The actual lantern has a sensor on the front with a pcb inside
    So I can't see the need for this extra wire
     
  4. terrymac

    terrymac Well-Known Member

    Did you check the wiring at the switch for loose connection ?
    Did you check continuity across switch ?
    On the old lamp ,not counting the earth ,were all 3 conductors terminated in the lamps terminal strip ,and were they all connecting to internal cables of the lamp ?
     
  5. Bazza

    Bazza Well-Known Member

    The third wire might be an over-ride connection, or it might be a feed to a second light.
    As Terrymac indicates, you need to find out what (if anything) is leaving the switch and then investigate why it doesn’t arrive at the PIR/light.
    From here, we can only guess.
     
  6. Suffolk

    Suffolk Member

    Thanks all. On my next visit I will head for the internal switch to check what voltages are around
    More importantly is this extra wire in the pattress box and what's it doing ?
     
  7. Bazza

    Bazza Well-Known Member

     
  8. spinlondon

    spinlondon Well-Known Member

    Some light fittings with PIRs, need permanent Live, Neutral and Earth to go to the sensor, then need a switched Live from the switch to the fitting.
    So there may be a junction box with 4 terminals.
    Permanent Live with 3 wires (one from the lighting feed, one to the fitting and the other to the switch).
    Neutral with 2 wires (one from the lighting feed and the other to the fitting).
    Earth with 2 wires (one from the lighting feed and the other to the fitting).
    The 4th terminal would then have 2 wires (one the return from the switch and the other for the grey wire to the fitting).
     
    Last edited: Sep 11, 2019 at 12:48 AM
  9. Suffolk

    Suffolk Member

    "Spinlondon" - "Some light fittings with PIRs, need permanent Live, Neutral and Earth to go to the sensor, then need a switched Live from the switch to the fitting."

    Many thanks, confirms what I found, just as I was about to post this update.

    Found this info on a Manufacturers web site
    the 4th grey wire manually switches the map, over-riding PIR
    lantern1.jpg + Manufacturers wiring
    lantern 2.jpg :- what I appear to have
    lantern 3: Proposed New lamp wiring with no PIR

    But as I said earlier all the wires have no voltage, must investigate indoors starting to see whats behind door switch
    My son reckons the lamp has been intermittent for some time but now failed permantly.


    lantern.jpg lantern 1.jpg lantern 2.jpg lantern 3.jpg
     

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