Problems Connecting a new Ceiling Light to an Existing Ceiling Rose


Postby Ebrownie » Mon Jul 20, 2015 6:57 pm

I am having some issues replacing a ceiling rose with a new light. I took down the ceiling rose and stupidly didn't pay much attention, I have done several of these already and didn't think it would be an issue.

There are 3 cables all of which have a red, black and earth wire . The 3 earths have been tied together. One of the blacks was also not wired to the ceiling rose and had a piece of white electrical tape over the end of it.

I assumed that I just had to connect one of the blacks to the live, the other to the neutral and the 3 reds together in a separate block. I did this and nothing happened. Tried swapping over the two blacks and nothing happened. (Incidentally none of the blacks had been marked as switched live with red tape over them). I decided it was probably sensible to wire one of the reds into the live so I tried each one in turn with the two blacks connected to the neutral. The third red wire turned the light on but it won't turn off at all. It now only switches off at the breaker. I have also noticed that the ceiling lights in the two adjacent rooms aren't working either now.

I hope this explanation makes some sense, apologies for it's length, I am thoroughly confused by the whole thing.

Please help!
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Postby ericmark » Tue Jul 21, 2015 6:41 am

OK ignoring earth wires as they just all connect together I will go through the other wires.
Three reds will be feed in (that’s the one which works the light) feed out (that’s why other lights don’t work) and feed to switch. As you have said all need to go together.

The three blacks will be neutral in, neutral out and line return from switch.

The only safe way is to switch off mains and then with a continuity tester (this could be a door bell, multi-meter, or any other item able to test between two wires) test each of the three cables in turn switching the light switch on and off until the switch wires are identified. Once identified mark the black with tape or similar then connect up three reds together but not to light, two blacks together and to neutral of light and remaining black with new tape to line of lamp.

Although you may be tempted to just try each black in turn as being switch wire this is not a good idea as it could produce a dead short and damage the light switch or MCB.
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Postby Ebrownie » Wed Jul 22, 2015 7:00 pm

Thanks. I actually have a multimeter to test for the switch cable. The only trouble is that one of the black wires has white electrical tape wrapped around the end of it and was never connected to the ceiling rose... Could there be a reason for this? If as you say they are all looped? I don't want to now connect this up when it may cause further problems.

I have read in several places to connect the three red wires together in a block before testing for the switch wire, but I have also read to check each cable individually as well. What is the best way to do this? Thanks
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Postby ericmark » Fri Jul 24, 2015 8:59 am

Much depends on your skill. For an electrician he may feel confident that he can work on a live circuit, but personally I would where possible work on dead circuits.

My meter is a clamp-on which means easy to use the clamp to dangle meter from a light fitting. I also have crocodile clips for the leads so I can clip onto wires leaving the meter set to buzzer and walk away and flick the light switch.

Using another meter it may mean two people with the one at lamp having three arms and hands one for each wire and one to hold the meter.

So likely it means getting some clips even if cloths pegs to hold wires to meter and a set of steps to place the meter on, but assuming there is a buzzer built into the meter working dead and testing every wire until switch wires are found is likely the best method.
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