(ceiling rose)... identifying an unmarked switched live.

[uganooll0]

Hi, any ideas as to how I can safely identify the switched-live from the 2 other black wires?

Will the switched-live likely be in the flex which is heading towards the switch?

Any help much appreciated.

 

[sparky_uk04]

if you have a continuity tester that would help.

turn power off turn s/w on and test each black wire with the live wires and you should get contimuity an the s/w live.

 

[MANDATE]

Yes! the cable that heads towards the switch should have a red 'live' wire and when the switch is on the black wire should be 'switched live'. This black wire should have red sleeves at each end to identify it.
At the ceiling rose this 'switched live' goes to the terminal block with two terminals along with the brown from the lamp.
If your blacks are not connected and there is no sleeving, you can use a electrical testing screwdriver. With the switch off non of the blacks will show live but with the switch on, the one your after will show live.

 

[uganooll0]

Thanks for the ideas guys; very useful. I'll see if I can find a continuity tester/electrical testing screwdriver.

So once I have found my switched-live, can I just double check.. is this (below) the correct way to use my other wires?


(The ceiling rose has 1 block with 3 terminals)

3 reds - all to a single terminal in a floating block

3 green/yellow - to single earth terminal on the rose

2 blacks - to single neutral terminal on the rose

1 black/red (switch live) to single live terminal on the rose.

 

[ban-all-sheds]

Don't use an "electrical testing screwdriver" - get some proper test equipment.

Yes you are correct about the wiring of the rose.

Shame you didn't observe which black wire was on its own before you took the rose off....

 

[uganooll0]

Thanks ban-all-sheds, what proper test equipment would you suggest?

and observing beforehand!.. I wish you'd told me that earlier.

 

[ban-all-sheds]

In decreasing order of preference (although it's useful to have all of them)

1) A multimeter

2) A "combi-check" tool like this sort of thing:

3) A proximity voltstick like this sort of thing:

 

[uganooll0]

Excellent. I'm borrowing a multimeter this afternoon.. many thanks for the knowledge & pics.

 

[uganooll0]

The results of the multimetering were curious, can anybody suggest a next step?

Cable 1: continuity present or broken by upstairs (2 way swtch), downstairs (2 way switch) has no effect on continuity.

Cable 2: continuity ok (Bathroom switch)

Cable 3: continous circuit and uneffected by any switches.


I'm guessing on Cable1 -the downstairs 2way is incorrectly wired, but Cable 3, I have no idea.

 

[TexMex]

At the ceiling rose you should have three cables. Each cable will have a red and black core. The cable that doesn't go BANG when you short out it's red and black cores, is the switched pair. Simple