2 way switching using earth

[ccam108]

Hi

I've been meaning to add a second switch for a lighting circuit near the back door so you don't have to walk all the way to the front to switch on lights. I know that the new switch position is along the switch wire route for the existing switch, so my question is this. Instead of replacing metres of twin and earth with 3 core and earth, can I use the existing cable and use the earth as the third core assuming all is sleeved properly at the switches. The only thing that will be unearthed is a plastic 1 gang switch in a dry lining box. If that sounds too confusing I can add a diagram.

Colin C

 

[Spark123]

No - you must never use the earth core as a live conductor.

 

[ccam108]

That's what I thought. Looks like I'm gonna have to get some 3 core and earth.

Thanks for the help.

Colin C

 

[toasty]

You could use a relay in or near the ligtht fitting if replacing the cable was a real pain in the you know.

But it would have to be an exceptional circumstance to warrant the extra cost and complexity

 

[ccam108]

How would that work then?

I'm a EEE student so I know my way around circuit design but I'm trying to get my head around what you are suggesting.

Colin C

BTW, I know that my course in no way gives me any qualification to do electrical work, but I'm no idiot, so I am a competent DIYer. Just thought I'd add before someone thinks I'm unaware of that.

 

[ccam108]

Just thought, is there any reason I can't just run a red or brown single alongside the existing t&e? The cable runs loose along a ceiling void.

Colin C

 

[ban-all-sheds]

If you can install a 2nd cable to run alongside the existing one is there any reason why you can't replace the existing one with 3C+E?

 

[ccam108]

That's a very good point lol.

Just got the idea from reading previous posts here. Obviously didn't switch my common sense on!

Colin C

 

[Space cat]

Some electronic switches can be used in conjunction with a second, standard switch using only two interconnecting wires. We have one that can be set to switch a light on and off at pre-programmed times. It has an extra terminal that allows it to be used in a two-way switching setup but only two wires go to the remote switch: one from this terminal and the other from live feed. One drawback of our old switch is that it doesn't work properly with fluorescent lights but newer versions might be better.

 

[toasty]

How would that work then?

I'm a EEE student so I know my way around circuit design but I'm trying to get my head around what you are suggesting.

Just use the existing switch to switch power to a SPDT relay, then use the SPDT contacts as the 'virtual' 2way switch.

 

[Spark123]

I've never liked the idea of using a relay as it creates another point of failure.
If you put 3c+e across you can even tie the old 2+e to it and use it as a pull wire providing it isn't clipped in under the floor.

 

[holmslaw]

..

 

[Spark123]

If it runs between the switch and light absolutely nothing, however it would acheive the same result as the original post but safer.

 

[toasty]

I've never liked the idea of using a relay as it creates another point of failure.

I agree, but if (and only IF) running a new length of cable is massively inconvenient or expensive then it is a viable alternative.

 

[ColJack]

seeing as the new switch is " along the switch wire route for the existing switch" then you pull the switch wires back from the switch and down to the new one, then run a 3core between.