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new light fitting very dim

Discussion in 'Electrics UK' started by gdp14, 21 Feb 2010.

  1. gdp14

    gdp14

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    hi
    this morning i had two light fittings working fine, controlled from a single dimmer switch.
    i have replaced one light fitting which involved moving the ceiling rose slightly, so the wiring to that rose was disconnected.
    i thought i was very careful to reconnect in exactly the same way once moved, but now both fittings are extremely dim and do not get brighter or dimmer when the switch is operated!
    there are four twin and earth cables coming in, three red connected together, three black connected together which feeds the fitting, and one red and one black with red sleeve connected which also feeds the fitting.
    the second unaltered light fitting has only one cable running to it.
    i have reconnected the black with red sleeve with each of the red cables in turn, with the others remaining together, which has meant no lights and constant light with no effective switch in turn.
    i have swapped the new fitting for a 40w pendant and the problem remains the same.
    ?? where did i go wrong?
    any help gratefully received
    thanks
     
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  3. Johnmelad502

    Johnmelad502

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    Have a look Here
     
  4. Lectrician

    Lectrician

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    You have confused the switch drop cable with a loop cable.

    You need to determine which cable is the switch drop and which is the switched loop to the other light. Once you know these you can reconnect correctly.

    You really need a multimeter to be able to do this (or if it's a loft you may be able to trace the cables easily).
     
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  5. gdp14

    gdp14

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    thanks
    i have access to a multimeter but don't know what/how to test
    i know which cable supplies the second fitting which just leaves three
    how do i test for which is the switch drop, no loft available unfortunately!
     
  6. sparkwright

    sparkwright

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    With the power OFF at the mains.

    Set the meter to resistance (ohms symbol looks similar to R).

    You will observe if you put the leads together you get a reading and perhaps a beeping sound. That shows you have circuit continuity.

    Put the light switch to on position (still with the power off).
    Put tester between red and black of the cables you cannot identify.
    See which cables give a reading.
    Now turn the light switch off.
    See which of those cables now do not give a reading.
    That is the cable which is the switch cable.

    Fit a red sleeve on the black wire. This is the switched live which goes to the live of the light fitting. Also in this terminal will be the red of the cable that goes to the second light fitting.
     
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  7. Taylortwocities

    Taylortwocities

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    You already have identified the switch drop :rolleyes:
     
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  9. ban-all-sheds

    ban-all-sheds

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    Fiddling with something when you didn't know how it worked.
     
  10. wingcoax

    wingcoax

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    The black wire with marking is the sw return and goes to the double connection at the side of the rose.
     
  11. StephenW

    StephenW

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    You might want to check that the dimmer switch hasn't gone kapput - mine did last time a bulb blew. Try swapping it out for a normal on/off and see if the lights are still dim.
     
  12. Damocles

    Damocles

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    As the last guy said, it is possible the dimmer has failed and the wiring was fine, but most likely the wires got mixed. Two lights will glow dim if you have wired them in series instead of parallel, which is to say the electricity going through the first and then the next instead of into both at the same time.

    The cable with the sleeving should go off to the switch. Its red wire should join up with power coming to the light fitting. The sleeved black should join with a red going to the other light fitting and also connect to the live terminal in the fitting you are working on. It is sleeved to show it is sometimes live even though it is coloured black. All the other blacks should be joined together and connect to the neutral on the fitting. You have four cables, so the fourth ought to be taking power off to the next light in the chain. So there should be three reds connected together, power in, power out, and the red going to the switch. Then the sleeved black connected to one red and the fitting. There is a diagram of this in the link by the first poster.

    Is it fixed or do you need help sorting out the mixed up wires? The tricky one, the switch, is already done because it has the sleving on it.
     
  13. Taylortwocities

    Taylortwocities

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    Look.

    ALL of this and how to do it is in the WIKI. Why don't people look at words that say

    " Please see if the answer to your query is already covered by the Wiki "


    Look, I'll make it easy for you:

    Go to this link http://www.diynot.com/wiki/electrics:lighting:single_way_lighting

    scroll down until you get to the diagram that is called

    "2 Lights on one switch using loop in method"

    Follow the wiring diagram.
     
  14. DIYnot Local

    DIYnot Local

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