What on earth is this!....well what on neutral anyway!

[Beefcake daddy]

Sorry for the essay!

Thought I had it all figured out with this lighting malarky, till I encountered this little fellow lurking amongst the rafters..

Basically there's a double switch on my door frame, left hand switches one light, right hand did switch another until it was removed. Everything worked lovely until I thought I'd use the right hand switch to control a new light in different location. At junction box, identified what I thought must be the switched live that was redundant (left hand junction box terminal on pic), disconnected it, so time to disconnect t'other end at the switch. Expected to see each switch wire going to one half of switch only, but turns out the live from each is paired with the return from the other.... In junction box there is a one and earth coming from the live terminal which dissappears off towards the landing light. Think to myself, must be something to do with two way switching, but yet neither of the switches connected control the landing light, which works lovely!

What is this wire? Is it a 'borrowed' live or neutral or something? I'm a bit worried as if it is I could have killed myself last night after reading up in the 'for refernce section'.

Anyway, fact of the matter is, I went and removed the redundant cable from junction box to switch, connected my switched live from the rose on the right of pic to what I thought it should be, ie live to com, return from L1 and light did not work anymore.

Gave up, rewired as it was originally and yep you've guessed it light refused to come back on. Think I must have killed the switch or my halogen bulb or something. Gonna employ my multimeter tonight to try and fathom this out with a bit more science...

 

[mapj1]

As drawn, its either a borrowed live or the supply to the whole lot and neutral is borrowed..
The left right confusion at the switches is amusing but sadly not all that unusual - just correct it. Make sure it is what you think - there may be lights that are between two lighting circuits, or one of them may be neutral switched.

 

[Beefcake daddy]

Cheers mike, I did notice that on the back of the switch there was an 'N' marked in pencil near to one of the L1 terminals, maybe it is a switched neutral...

I think I'll be ok as long as I keep all the power to the lighting circuits off, just in case the 'borrowed' cable is keeping power in to the circuit I'm working on.

 

[ban-all-sheds]

At junction box, identified what I thought must be the switched live that was redundant (left hand junction box terminal on pic), disconnected it, so time to disconnect t'other end at the switch. Expected to see each switch wire going to one half of switch only, but turns out the live from each is paired with the return from the other

Which is a nuisance, but remedied in a trice by swapping over the permanent lives between the two COMs. As originally installed, though, it was electrically identical to the more usual way of doing it, not in the slightest bit dangerous, and would have worked 100% properly.

In junction box there is a one and earth coming from the live terminal which dissappears off towards the landing light. Think to myself, must be something to do with two way switching, but yet neither of the switches connected control the landing light, which works lovely!

It couldn't be anything to do with 2-way switching as it's a permanent live going somewhere - it hasn't originated at a switch.

What is this wire? Is it a 'borrowed' live or neutral or something?

I guess that at the other end it could be connected to the live of another circuit, but surely you'd have spotted that when you isolated the light circuit but all of the lights carried on working? And how could it be a neutral of any sort when it's clearly connected in the LH JB to the lighting loop live?

I'm a bit worried as if it is I could have killed myself last night after reading up in the 'for refernce section'.

But if you turned off the power to the lighting circuit, and verified that it was dead, then you were not at risk.

Anyway, fact of the matter is, I went and removed the redundant cable from junction box to switch, connected my switched live from the rose on the right of pic to what I thought it should be, ie live to com, return from L1 and light did not work anymore.

If by that you mean that you did swap the wires feeding the two switch COMs over then it should have worked. If it didn't then either the lamp has coincidentally failed, or the wiring is not actually as you have shown it - in the diagram you posted, the switch on the right (which may be the switch on the left when it's in place and viewed from the front) would have controlled the light attached to the rose, and the switch on the left (right) would have controlled a light wired to the two left-most terminals of the LH JB.

Gave up, rewired as it was originally and yep you've guessed it light refused to come back on.

Then either the lamp has coincidentally failed, or the wiring was not actually as you have shown it, or you didn't actually reconnect it as it originally was.

Think I must have killed the switch or my halogen bulb or something.

Try a new lamp first.

 

[ban-all-sheds]

Cheers mike, I did notice that on the back of the switch there was an 'N' marked in pencil near to one of the L1 terminals, maybe it is a switched neutral...

In the diagram above there are no neutrals going anywhere near either of the switches...

I think I'll be ok as long as I keep all the power to the lighting circuits off, just in case the 'borrowed' cable is keeping power in to the circuit I'm working on.

Surely you didn't simply turn off the MCB for that circuit and not check that it really was dead before beginning work?

As you have no idea what that lone live does, you should either kill power to the entire house (you can't be absolutely sure that it isn't an incoming switched live from a different circuit altogether), or disconnect it at the JB and make the end safe with a bit of choc-block.

 

[Beefcake daddy]

Beefcake daddy wrote:
At junction box, identified what I thought must be the switched live that was redundant (left hand junction box terminal on pic), disconnected it, so time to disconnect t'other end at the switch. Expected to see each switch wire going to one half of switch only, but turns out the live from each is paired with the return from the other

Which is a nuisance, but remedied in a trice by swapping over the permanent lives between the two COMs. As originally installed, though, it was electrically identical to the more usual way of doing it, not in the slightest bit dangerous, and would have worked 100% properly.

Yup, that's what I did, but had no joy after I'd switched the lives I put the power back on, tried the switch, no light.

You're dead right though B-A-S, I went through everything you've mentioned pretty much last night, that's when I decided I'd gone past my point of knowledge and safety, knew it was time to stop. I thought it quite possible that I'd knocked a wire loose somewhere, but had tightened everything up.

I forgot to mention in my stupidity to need to know why it wasn't working I opened the switch up, there was a wee bit of charring on one of the connections - that could prevent a circuit being made right?!

 

[Beefcake daddy]

Surely you didn't simply turn off the MCB for that circuit and not check that it really was dead before beginning work?

Only way to get that 'just out of bed' trendy haircut I'm sporting!

 

[ban-all-sheds]

 

[mapj1]

Thats certainly a good ploy - plus if in doubt check its dead before touching - probably worth trying to map it out as you go - expect the unexpected !

 

[Beefcake daddy]

Eventually traced this problem back to a loose connection with my multimeter, seems I had the wiring right from the beginning, feel a bit of a dumbass but who cares -- lights work so I can get back to my tiling now!

Thanks for all your help guys, I really appreciate the time you took responding to my newbie questions you've probably seen asked a thousand times before