Ceiling has 3 sets of wires for lighting

Discussion in 'Electrics UK' started by OllieOllie, 28 Mar 2021.

  1. terryplumb

    terryplumb

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    Does your meter have a continuity facility ,or any other functions ,or is it just a voltmeter ?
     
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  3. Ismi01

    Ismi01

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    It is this one here
     

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  4. terryplumb

    terryplumb

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    Do you know how to use it to measure resistance ?
     
  5. terryplumb

    terryplumb

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    Ω this is the symbol for resistance on your meter
     
  6. Ismi01

    Ismi01

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    Kind off yes that’s the ohms symbol?
     
  7. Aragorn84

    Aragorn84

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    with the power turned OFF at the main switch, use the Ohms setting and test between brown and blue on each cable:

    Before you take any readings, note what the meter shows when connected to nothing, and then touch the probes together and note what it shows when measuring a close circuit/dead short. It should show something like "-" or "-1--" when connected to nothing, and should change to showing a very small number when the leads are connected together.

    Then you can test across the brown and blue on each cable.

    Note the readings.

    Then operate the switch, and repeat.

    One of the readings should have changed from "open circuit" to a very low resistance (or vice versa if the switch was already on). Meters have different ways of showing open circuit, but you can see what it does when connected to nothing at all as per the above.

    If so, that cable is the switch drop. Mark it in some way (even writing on it with a sharpie would do)
     
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  9. Harry Bloomfield

    Harry Bloomfield

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    You can almost certainly expect a low resistance between brown and blue, on the two which do NOT go to the switch - so make sure the low resistance does come and go with the operation of the switch. It might be easier to get a partner to operate the switch, as you hold the meter on the brown and blue - you need to be absolutely sure you have found the correct cable.
     
  10. Andrew Ryan Da Costa

    Andrew Ryan Da Costa

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    Hi Team

    I have a very similar problem when i went to swap my main living room ceiling light. In total i had 3 wires. In each of those main wires i had 3 wires coming out red, black and green.

    I had a spare bulb and wire connection so that i could check which one was live and which one was switch. What i found out is I had 2 live wires where the bulb came on.

    Meaning i first connected the red and black from the main wire, the bulb came on. After that i connected the red and black from the second main wire and bulb came on. Later i connected the red and black wire on the last main wire and the bulb never came on, which means this is switch.

    My only question now is why do we have 2 live wires in the rose ceiling outlet of a 1930 house ?
     
  11. SUNRAY

    SUNRAY

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    It sounds like you may have a LIGHTING RING CIRCUIT as opposed to a radial circuit.

    One regular poster is likely to come on here and say they don't exist.
     
  12. Harry Bloomfield

    Harry Bloomfield

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    Well, I will not say they do not exist, rather that such a ring is entirely unnecessary and more likely to be an accidentally created ring by who ever wired it, or a later error.
     
  13. bernardgreen

    bernardgreen

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    It does provide single fault tolerance. One loose / broken connection can be tolerated leaving all lights functional.

    People will say that a loose / broken connection should not be tolerated, provided it does not create a hazard it is preferable to the hazards of a house with some of the lighting not working
     
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  14. SUNRAY

    SUNRAY

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    I'll agree they are generally not necessary but I've worked on enough to know they are not 'that rare'. The other thing of course is how many people actually test for and identify a ring? I know that I for one will ensure I can identify the switch cable, isolate and change a fitting without ever testing to see which of the loop cables is in or out. For that reason I reckon that 90% of the ceiling light fittings I've worked on could very possibly be unidentified rings and I imagine the same is true for many others on here.
     
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