# Electrical Advice - Light Switch



## mark328 (Aug 1, 2010)

Morning All,

Just throwing this one out there if anyone has any thoughts.

2 gang, 2 way light switch in hallway.

Left switch controls hallway light, which can be turned off from either end of long hallway.

Right switch is supposed to be supply to outside lantern to side of front door (no PIR).

What is confusing me is between L1 Left Switch and COM of Right Switch there WAS a link.

I know L1 should be Switch Live, with COM being the permanent live, but why was there a link between L1 and COM, I would of thought that if there was going to be a link it would be between COM/COM, ie to provide a supply to Right Switch?

I am installing a new lantern outside but was getting no reading from live wire outside with Right Switch open or closed, my suspicion is that I would have if the Left Switch was on?



TIA


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## Snowglobe (Jan 12, 2008)

Have a look at this
http://www.electronics-project-design.com/LightSwitchWiring.html

You will need to work out which of the cores is 'live' and this will probably have a link or jumper to the other light switch for the outside light, which will work as a one way switch.

Be careful if you are not confident working with electricity as you can still get a shock from the neutral circuit if you're not careful


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## mark328 (Aug 1, 2010)

Snowglobe said:


> Have a look at this
> http://www.electronics-project-design.com/LightSwitchWiring.html
> 
> You will need to work out which of the cores is 'live' and this will probably have a link or jumper to the other light switch for the outside light, which will work as a one way switch.
> ...


Cheers for the reply Snowglobe. I'm pretty good with electrics, well I have all the qualifications but not practised as completely changed jobs!

As said, when I removed the switch plate, I had 2 cables, 1 of which only had a BLACK( the red cut off further up the sheath), the other had RED and BLACK going into L1 and L2 respectively, that was all on 1 Gang side, then there was a 'bridge' from L1 to COMMON of the 2nd Gang, with the L1 in that side going out to the outside light.

When I disconnect ALL from the switch and test between earth and the 2 blacks and red, I get 0v at COMMON BLACK, but 230v on the BLACK and RED from L1/L2, depending on the position of the switch at this wall (porch) and the position of the switch in the hallway.

My understanding is that the COMMON is the incoming live, which is then 'broken by L1/L2 depending on where you switch the light from (i.e. Porch or hallway).

House is so old god knows what's been done!!!


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## Dannybutcha (Mar 10, 2017)

would i be correct in saying that the voltage changes between the L1 and the L2 when switching so you never actualy have a constant 230v at either terminal?


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## mark328 (Aug 1, 2010)

Dannybutcha said:


> would i be correct in saying that the voltage changes between the L1 and the L2 when switching so you never actualy have a constant 230v at either terminal?


Exactly!


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## mark328 (Aug 1, 2010)

So effectively I can turn the outside light on/off using the Gang 2 switch, but as the 'supply' for this gang is from L1 of Gang 1 (L1 to COMMON bridges), the switch for the outdoor will only work if L1 is in play so to speak.

I've tried linking COM Gang 1 to COM Gang 2 but nothing.


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## Dannybutcha (Mar 10, 2017)

Im pretty sure all those years ago the 2way switching was done a bit differently to how we would do it now, being that they would "borrow" a live from another light at one switch (possibly the other switch may well have a link in at the common?) then use a 2core to the other switch with a single being at that commin providing the switch live to the light. If this makes sense? 

You were correct in what you were saying though that common would be live and L1 switch live on a 1way switch but that does change a bit on 2way.


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## mark328 (Aug 1, 2010)

Dannybutcha said:


> Im pretty sure all those years ago the 2way switching was done a bit differently to how we would do it now, being that they would "borrow" a live from another light at one switch (possibly the other switch may well have a link in at the common?) then use a 2core to the other switch with a single being at that commin providing the switch live to the light. If this makes sense?
> 
> You were correct in what you were saying though that common would be live and L1 switch live on a 1way switch but that does change a bit on 2way.


Yes it does, I'll have another bash tomorrow.

Thanks


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## Dannybutcha (Mar 10, 2017)

Someone else might have more advice or another solution but the way i see it is that at the light switch there wont be a permanent live so to speak therefor if the 2way is switched the wrong way to suit your outside light it will go off? A little thought to try though would be the light that the 2way is switching should have that black being the switched live therfor if there is a red at either end cut off you could reconect the red into the permanent live of the fitting (if there is one) then into common of the outside switch using the original live for outside to be put back into L1. Hope some of that helps &#55357;&#56834;


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