Extra wire in ceiling rose

[gdubya]

Hi,
Sorry to resurrect a dead thread, but I've got a very similar situation: I've just moved in to a house and decided to replace a hall ceiling rose with a different one. Foolishly I forgot to make a note of the exact connections. Now I have 3 sets of wires from the ceiling: 3 neutrals (one with a red tag, which I assume to be the switch cable), 3 reds, and 3 earths. But there is also one extra black (presumably neutral?) wire and I'm not sure what it's for. There is a 2nd light on the circuit, upstairs (for some reason that light is on the downstairs lighting circuit, even though it's upstairs). Could it be related to that?

Update: the circuit diagram seems to be very similar to this one pictured by breezer, except that the extra black wire is not pictured

 

[gdubya]

oop, sorry!

 

[plugwash]

Do you mean there is a second light controlled by the same switch? if so what is the wiring in that second light?

 

[gdubya]

Sorry, I didn't explain the situation correctly. There are two lights (one on the landing upstairs, and one in the hallway downstairs), and each has its own switch. The light upstairs has two switches (one on the landing and one downstairs). The light downstairs has only one switch. The light upstairs is wired as I expected (i.e a single wire each for earth / live / neutral), but the light downstairs has the extra wires (normal for a ceiling rose?): 3 earth, 3 live, 3 neutral, plus the extra "neutral" wire. One of neutrals out of the three sets of wires is marked with a bit of red tape, indicating that it is the switch cable.

 

[plugwash]

The light upstairs is wired as I expected (i.e a single wire each for earth / live / neutral)

That likely means there is a junction box somewhere, can you follow the cable in the loft and find out where is goes?

BTW the black in the switch cable is not a neutral, it is a switched live.

but the light downstairs has the extra wires (normal for a ceiling rose?): 3 earth, 3 live, 3 neutral.......................One of neutrals out of the three sets of wires is marked with a bit of red tape, indicating that it is the switch cable.

That bit is normal

plus the extra "neutral" wire

That bit isn't and therefore we need to figure out what that wire is.

What is the wiring in the switches like?
Does the cable from the light upstairs go to a junction box you can access and if so what is the wiring like in that box?

 

[ban-all-sheds]

That bit isn't and therefore we need to figure out what that wire is.

A neutral from the correct circuit to avoid a borrowed one at the landing light?

 

[plugwash]

It could well be but the only way to know for sure is to find the other end of it. Connecting it without figuring out what it is seems rather irresponsible to me.

 

[ban-all-sheds]

Absolutely.

 

[gdubya]

That likely means there is a junction box somewhere, can you follow the cable in the loft and find out where is goes?

Unfortunately not. The mystery cable appears in the ceiling of the light on the ground floor, and I can't see where it goes. I have no idea which one in the loft it is. I guess I could do a continuity test to work it out, but that might take a while.

BTW the black in the switch cable is not a neutral, it is a switched live.

Yeah, the switched live black cable has a bit of red tape on the end, so that I can keep track of that one

plus the extra "neutral" wire

That bit isn't and therefore we need to figure out what that wire is.

What is the wiring in the switches like?
Does the cable from the light upstairs go to a junction box you can access and if so what is the wiring like in that box?

I'm not sure. I haven't examined the switches yet. I'll have another look in the loft tomorrow (I'm stuck at work right now) to see if I can find a junction box.

BTW, I tried wiring it up and putting the spare black cable in with the other two neutrals and everything seemed to work ok, but as you said it's not a good idea to leave it connected without knowing exactly what's going on!