Additional Neutral at lighting JB?

[F54Mini]

Hi

I am in the process of changing some old school light fittings to modern ones with a ceiling rose.

It’s a 60s house so uses junction boxes which is fine and I have worked out what cable goes where, I have power in, cable to switch, cable to light fitting and power out but there seems to be a fifth cable which is just connected to the neutrals, the line appears to be cut.

See the image attached, its the cable at the bottom.

I’m not going to replace the JB, merely run a switched line and neutral to the ceiling rose but I am wondering what the extra cable might be doing?

I can trace it but requires pulling up several 8x2 OSB boards in the loft which are screwed to the joists.

Ta

 

[ericmark]

Oh dear, clearly pre 1966 wiring. Before 1966 earths were not required to lights, and regulations are not retrospective, so as long as you do no work on the system it can remain as is.

But as soon as you make changes, then the earths are required.

 

[ericmark]

Oh dear, clearly pre 1966 wiring. Before 1966 earths were not required to lights, and regulations are not retrospective, so as long as you do no work on the system it can remain as is.

But as soon as you make changes, then the earths are required.

To touch it is to open a can of worms, I have tried in the past to connect earths, and gone round and round in circles, wishing I had never started.

 

[F54Mini]

Oh dear, clearly pre 1966 wiring. Before 1966 earths were not required to lights, and regulations are not retrospective, so as long as you do no work on the system it can remain as is.

But as soon as you make changes, then the earths are required.

Required by whom? Current regs presumably?

On the basis the regs are not a person who is going to challenge me and the light fittings are all plastic, I am happy to change the ceiling rose to a new one.

I was just curious as to what the additional neutral only cable might be for.

Sockets all have earths which are connected and the cables to the light fittings are twin and earth, the earths are just not connected.

 

[ericmark]

As you point out the neutral is a single cable, the line and earth not used, so it would seem likely some where some thing was short of a neutral, most likely would be a switch where some electronic version needed a neutral.

I know in my own house a 4 gang switch has two neutrals and two line feeds, and there was a borrowed neutral, which did not become apparent until the consumer unit was changed and the RCBO would not hold in.

The error could have been made when house first built, as allow clearly dangerous it is not some thing hunted for, which is why so dangerous as so easy to miss. And it means when a circuit is isolated it can be made live due to some other circuit being used.

I would simply disconnect and see what stops working.

 

[oldbutnotdead]

Your stray black core (just because it's black doesn't mean it is neutral) may have been (or may be) part of a 2 way switching setup. Only way to tell is take the switch plates off and have a look.

 

[terryplumb]

Your stray black core (just because it's black doesn't mean it is neutral) may have been (or may be) part of a 2 way switching setup. Only way to tell is take the switch plates off and have a look.

If it's connected to the circuits neutral in that junction box ,as it appears to be ,it's a neutral !!

 

[oldbutnotdead]

If it's connected to the circuits neutral in that junction box ,as it appears to be ,it's a neutral !!

Ahh, is that Sharpie squiggle saying PWR? Fair enough then on that one

 

[sparkwright]

Which room does the jb serve?

Are there earth wires in the cables that have been snipped out/twisted together under the jb?

It looks like it's a neutral, but there is a slight chance it could be a live not sleeved red.

Sometimes. a neutral can be 'borrowed', and sometimes a borrowed neutral can be applied to a different circuit - which is not good.

Such an arrangement will cause RCDs to trip at the consumer unit, and such an arrangement would need sorting out if you had a new consumer unit with RCDs, if you didn't have them before.

 

[davelx]

Does the same fuse/MCB feed both upstairs and downstairs lights? Very common for older houses to only have a single lighting circuit.

If so, if you follow that cable I am willing to bet it will be the neutral for the upstairs landing light, which is probably on a two way circuit where the live is fed to the downstairs switch and just the "strappers" go to the upstairs switch, with just a switched live from there to the lamp therefore requiring a neutral to be taken from elsewhere on the lighting circuit.