Lighting circuit - black wire?

[jwadd215]

Hi,

On checking two light switches that operate my outside lights front and rear, both work, I've discovered there is an unused black wire as per the picture, just wondering is this is normal?

It is a spare switched live or something?

Should it have been connected to L1?

Thanks you,
James.

 

[littlespark]

The black is part of a 3 core and earth cable, and there should be a corresponding grey.

It may have been once used as part of a two way circuit, or an override switch for a sensor light.

If it’s not connected, and everything works as it should… you can leave it…. Although you could just put a connector or the end….


It would be interesting to know where the other end of the cable goes.

 

[jwadd215]

The black is part of a 3 core and earth cable, and there should be a corresponding grey.

It may have been once used as part of a two way circuit, or an override switch for a sensor light.

If it’s not connected, and everything works as it should… you can leave it…. Although you could just put a connector or the end….


It would be interesting to know where the other end of the cable goes.

It's a new build and I am the first occupant.

Ah, you can just about see a grey in the above, looks like it goes into the connector block with the neutral, so assuming it's acting as a neutral?

I have just been and taken the cover off one of the outside lights, the one that matches the switch above and it appears the black is unused and you can just see where they've cut it off.

Many thanks.

 

[westward10]

As above it was probably for an override.

 

[littlespark]

At least this gives you the option of a different type of light fitting where an override may be required

 

[EddieB]

The Grey should b Blue sleeved and the black which has been cut off one end it should be cut off the others its of no use whatsoever. Not a very good example of new build electrics I'm afraid

 

[littlespark]

Yes, a bit strange cutting the black completely back at the light, but not at the switch.

Unless there's spare cable that can be pulled through the wall... The black could be utilised with a different type of fitting

 

[EddieB]

Yes, a bit strange cutting the black completely back at the light, but not at the switch.

Unless there's spare cable that can be pulled through the wall... The black could be utilised with a different type of fitting

Yes Indeed, my thoughts exactly

 

[jwadd215]

In the interests of safety is it worth sleeving the black wire with earth sleeving and putting it to earth on the terminal in the back box?

 

[Risteard]

In the interests of safety is it worth sleeving the black wire with earth sleeving and putting it to earth on the terminal in the back box?

Yes.

 

[jwadd215]

Yes.

With it being so short at the light end I don't think I'm going to be able to do anything with that end, would it then be acceptable to just earth it at the light switch back box end?

I've be told there could be a potential danger of induced volatge with unterminated cables.

Thank you.

 

[jwadd215]

It gets worse, the earth has been cut short left sleeved in the back of the light to one side, and the earth terminal on the casing ignored, told this is a C2.

 

[jwadd215]

With the black wire not used at either end and it being so short at the light end I don't think I'm going to be able to do anything with that end, would it then be acceptable to just earth it at the light switch back box end?

I've be told there could be a potential danger of induced volatge with unterminated cables.

Thank you.

 

[brianmoooore]

A voltage can be induced into the unconnected black wire, but since both ends are inaccessible when everything is back together, it poses no additional danger over the other live wires present..
The unconnected cpc at the lamp fitting is definitely something I would code C2 in an EICR and should be corrected by adding a short length of G/Y between the too short wire and the terminal, after checking that the cpc at the switch does actually connect back to the main earth terminal at the CU.

 

[jwadd215]

A voltage can be induced into the unconnected black wire, but since both ends are inaccessible when everything is back together, it poses no additional danger over the other live wires present..
The unconnected cpc at the lamp fitting is definitely something I would code C2 in an EICR and should be corrected by adding a short length of G/Y between the too short wire and the terminal, after checking that the cpc at the switch does actually connect back to the main earth terminal at the CU.

Yeah I was just wondering if I should put the unused black at the light swtch end to the cpc earth terminal on the metal back box or leave it as it is? at the light end it is so short it is just covered over with inuslating tape.

Yes I think the CPC at the light end is an apprentice error, I have since put it into a connector block and run a sleeved fly lead from the other end of the block to the CPC terminal on the metal light casing, I have then tested for continuity between the screw on the light switch and the metal outer casing and there is continuity.

 

[brianmoooore]

It's good practice to connect unused wires in cables to earth, but as I wrote, there's no real extra danger in this case to those who work safely.

 

[Simon47]

I'd have a special place in hell for ****** who cut off cores that they don't need now.
At our last house it had a gas cooker and a blank plate where the cooker supply had been. The *****s had just chopped the cores off, so reinstating it would have meant fiddling around to crimp extra long onto them - and then the crimps making the wires awkward to tuck in.
But that all part of the too common attitude of doibg what's easiest for you now and screw anyone coming along later.