Rogue 3-core-and-earth in lighting circuit

[SJM2014]

Hi,

I've encountered an unusual lighting wiring situation and would like a second opinion on whether I'm interpreting it correctly.

The below interpretation has been derived from purely looking at the two main lights and switches, I've not lifted floorboards etc.

The room is a lounge/diner, with a main light at each end, a switch at each end, and previously had 3 wall lights, which have long-since been plastered over.

Untitled

• SJM2014
• 30 Nov 2014
• 1

Starting with the bottom half of the diagram there is a single 2-core-and-earth cable coming in to the switch, wired normally, that controls the dining room light; the dining room is at the end of a loop-in circuit.

The top half gets more unusual, the switch has 3x 2-core-and-earth cables coming in and 1x a 3-core-and-earth cable coming in.

(In the below diagram circles represent separate cable blocks where the appropriate cores have been wired together.)

Untitled

• SJM2014
• 30 Nov 2014
• 1

The bulb as you would expect for the middle of a loop-in lighting circuit has 3 cables, two of which are the normal 2-core-and-earth, but also has a 3-core-and-earth cable coming in.

The bulb would appear to be wired normally apart from the rogue blue core coming from the cable.

Untitled

• SJM2014
• 30 Nov 2014
• 1

1) I interpret this to be that the wiring between the main lounge bulb and switch was done using the wrong sort of cable and someone just wired the blue core in to stop it floating.

2) On the switch, I interpret that someone has mostly taken out the wall lights from the switch itself (which would have once had 2 switches, one for the main bulb and one for the wall lights), but has wired in the blue core to stop it floating as previously mentioned and left in a single red wire from one of the 2-core-and-earth wall lights, serving no purpose.

My thoughts on the ways forwards is to

1) temporarily disconnect the blue core from the 3-core-and-earth cable at both ends

2) re-wire the rogue red wire from the 2-core-and-earth wall light into the twisted blocks

3) Assuming switch & light works correctly, then re-wire the blue core to stop it floating

All feedback gratefully received...

 

[deadshort]

I would disconnect ALL unused neutrals and unused switch wires to avoide problems in the future with the old wall light cables.

I would suggest you just make safe with connector block and leave in position.


Regards,

DS

 

[AndyPRK]

You could just leave it alone!


Its been wired like that to cater for the old wall lights.

I would also guess the dinning room switch was added at a later date

 

[AndyPRK]

I would disconnect ALL unused neutrals and unused switch wires to avoide problems in the future with the old wall light cables.

DS

I think you do need to keep a neutral at the switch because I think its being used for the dinning room light

 

[deadshort]

I did say unused

DS

 

[SJM2014]

I would disconnect ALL unused neutrals and unused switch wires to avoide problems in the future with the old wall light cables.

I would suggest you just make safe with connector block and leave in position.

Thanks, makes more sense than leaving wired-in even if probably harmless, so I think I will do that with the rogue blue core in the 3-core-and-earth cable; I think also for the rogue red core.

You could just leave it alone!

Its been wired like that to cater for the old wall lights.

I would also guess the dinning room switch was added at a later date

I know the 3x 2-core-and-earth are there for the wall lights, but the problem is one of them still has a single core wired into the switch, whereas I think it should be tied into a cable block like the other wall light cores.

I'm double-checking with a neighbour's lighting (same house design) but I'm almost certain the dining room switch is original.

Thanks for such quick responses!

 

[deadshort]

My rational for the disconnection of all unused wiring is simply the dreaded N/E short which could occur if the room was being redecorated and a wallpaper steamer or wet sponge was used on the wall with the old wall light wiring in it. If you sold your house it would take the new owner days to find the fault!

Also, we have heard of "live wall" syndrome at least you know it is safe if you disconnect the unused cables.

Well done on your very clear wiring diagrams.

Regards,

DS

 

[AndyPRK]

The cable coming out of the bottom left of the switch has very much been left connected, and I would assume required.

Have a go at disconnecting its red wire and see if everything (including the dining room light is still working).

Its also using the blue wire

 

[sparkwright]

All looks fine, can't see the problem.

The 3 core has been used to obtain the switch live for the lounge light, a permanent live to feed the switches, and a neutral to serve the wall lights.

Looking at the diagram of the switch, the bottom left cable is permanently supplying a live and neutral for something - possibly the dining room.

All you have to do is fully disconnect the wall light wiring.

Tip - don't cut off any un-used wires until you are certain everything works.

 

[SimonH2]

1) I interpret this to be that the wiring between the main lounge bulb and switch was done using the wrong sort of cable and someone just wired the blue core in to stop it floating.

No, they've done it that way for a reason. The blue wire is there to provide a neutral to other lights - without having to run a separate cable.
The alternative would be to run a T&E for the light switch, and a separate T&E for a permanent L&N for the other lights (or a separate single&E for just the neutral).

Using the 3&E means using just one cable.

Ideally, you would find the old cables for the wall lights and remove them. But, it's not unlikely that someone just cut them off and plastered over the hole. One of those cables will still have a permanent live - it's the one exiting to the left on the lounge switch diagram.

As a simple fix to make things safe, take the red & black cores for those three T&Es and connect them all to the earth terminal in the back of the switch. They won't all fit, so use a terminal block to common them together and then a short bit of offcut core to connect to the earth terminal. I wouldn't cut anything back - that's a sure fire way to guarantee that you'll want to resurrect something later* Leave the blue wire in the 3&E connected at the rose (no need to disturb anything there), and on it's own in a small terminal block behind the switch.

* At home, at some time in the past the cooker feed has been borrowed to feed a shower (no longer there) and the ********* cut the cores back in the back of the cooker switch box. Somewhere, there are a number of people who should have been having a burning sensation in their ears as I find out things about this new to me house.

 

[SJM2014]

Hi, thanks for all replies.

You're correct that is supplying a neutral to the lounge switch. It turns out that the permanent 2c&e live is actually supplying to the hall light switch on the other side of the wall, which is then supplying outside light and hall light. So the THREE wall lights were being supplied by the TWO disconnected cables; I figured this by looking at a neighbour's wiring which has the wall lights and it came from there.

From thereon in the two-way hall lighting continues the fun , but it's all comprehensible knowing the context.

I think the neutrals for the two cables with disconnected lives can be tied off with a cable block and then if all still okay, earthed with disconnected lives as suggested. Will try it.

Will be sorting out this weekend.

Once again, thank you all, I'll drop a post to let you know how it goes...

Edit: The neighbour's wiring to the lounge switch shows the live from the 3c&e is supplying the power to the wall lights by being wired into that part of his 2-gang switch as well as the one for the main lounge light.