Two way lighting mistake

[Jamie2106]

I've run a cable to convert an existing one way switch to a two way but only just realised I should have used three core and earth, I have used twin and earth.
Re-running the cable isn't an option as it's now been plastered and decorated.
Assuming there is no way to make it work with twin and earth, is it acceptable to use the earth wire as the third wire, with sleeving on to show it is live?
The switch is plastic but with a metal back box, to earth the back box could I take the earth from a socket that is a few inches to one side of the switch? It would just be a short horizontal chase between sockets and switch

 

[magicmushroom666]

No the earth core also protects the cable along the run, not just the item at the end

 

[ericmark]

These are expensive but likely less cost than re-decorate.

there is a way if the remote switch is one of a pair, but you seem to say that is not the case.

 

[ban-all-sheds]

is it acceptable to use the earth wire as the third wire, with sleeving on to show it is live?

No.

But if you could run a cable from the new switch to the light then you could have 2-way switching using the T&E link:

 

[John D v2.0]

It wouldn't be possible using just the one cable, if you're tempted to use the earth core (CPC) then a less bad option would be too borrow a neutral from upstairs, from the same circuit to comply with the regs and prevent RCD tripping if at all possible.

If it was me I'd use BA's suggestion, but I was also going to say if you can convert to ELV signalling before the switch (12v etc) you could use any cores. Someone Will let me know if that's incorrect!

 

[cjard]

Using a Fibaro dimmer or remote switch this becomes possible. It's a black box that has live, neutral and variable-live output, and a switch connector for any number of remote switches. You would put the fibaro box behind your master (existing) switch and connect according to which version of the box you bought:

If you bought a dimmer1 (discontinued, cheap now on ebay at a tenner ish when they come up) follow: http://www.vesternet.com/resources/application-notes/apnt-1
If you bought a dimmer2 (current model, about £40) follow: http://www.vesternet.com/resources/application-notes/apnt-111

Any number of switches are connected by wiring all their COM together and separately their L1 together (2 cores used). The CPC core of the T+E you ran should remain as an earth and be appropriately sleeved and conencted in all switches. Pressing any switch activates the dimmer. For best operation, you should change the switch out for a spring loaded momentary (push to make, release to break) switch (like a doorbell).

 

[Risteard]

No the earth core also protects the cable along the run, not just the item at the end

That's not actually true. A cpc must be terminated at every point in the wiring and not run in every cable - it's certainly not there to protect the cable. However that core in T&E is uninsulated which prohibits its use as a live conductor. Other than in 1mm^2 T&E it is also of a reduced cross-sectional area than the live conductors.

 

[Risteard]

a less bad option would be too borrow a neutral from upstairs, from the same circuit to comply with the regs and prevent RCD tripping if at all possible.

If it's the same circuit then it isn't a borrowed neutral. If it isn't the same circuit then it is an expressly forbidden and dangerous practice which should never, ever be advised.

 

[Jamie2106]

Thanks for the replies everyone. I can't get any wires from either upstairs (concrete ceiling) or elsewhere in the room and I can't justify the wireless controller. It's supposed to be a double switch at each end, to control two lights independently, so I have two t&e's in there. Might be best to just wire them together so both lights come on together, as I could then use four out of the six wires.

 

[Jamie2106]

Thanks for the replies everyone. I can't get any wires from either upstairs (concrete ceiling) or elsewhere in the room and I can't justify the wireless controller. It's supposed to be a double switch at each end, to control two lights independently, so I have two t&e's in there. Might be best to just wire them together so both lights come on together, as I could then use four out of the six wires.

 

[Nozzle]

Croc-clips. Love it.

Nozzle

 

[securespark]

isn't an option as it's now been plastered and decorated.

How?

 

[John D v2.0]

If it's the same circuit then it isn't a borrowed neutral. If it isn't the same circuit then it is an expressly forbidden and dangerous practice which should never, ever be advised.

I did say "less bad"! But agreed, I still think it's less dangerous than using a cpc as a neutral, but still likely to surprise people.

 

[Lectrician]

Thanks for the replies everyone. I can't get any wires from either upstairs (concrete ceiling) or elsewhere in the room and I can't justify the wireless controller. It's supposed to be a double switch at each end, to control two lights independently, so I have two t&e's in there. Might be best to just wire them together so both lights come on together, as I could then use four out of the six wires.

With four cores, you could two way switch at least one of your lights.

 

[PrenticeBoyofDerry]

I've run a cable to convert an existing one way switch to a two way but only just realised I should have used three core and earth, I have used twin and earth.

Oh-Dear! Should have researched that one or employed someone that understands two way switching and tests cables and circuit functions prior to plastering and decoration.
All options have been covered already, so if you are unable to implement any of them and unwilling to install correct cable configurations, your stuffed.