Confusing wiring on two-way switch?

[stavroshamster]

Hi Everyone,

Just joined after failing to find an answer on google.

We have a two-way switch circuit for the lights in our living room - they work fine.

Both two-way switches have a red wire going to the 'COM' terminal, a yellow wire going to the L1 terminal and a blue wire going to the L2 terminal. There is also an earth wire connected to the boxwork.

However, from wiring diagrams I have found online I was expecting a switch wire coming out of the L1 and L2 terminals of a 'master' switch with the other switch acting as a 'slave' - this is clearly not the case...

Is our setup an alternative way of wiring up the circuit, or is there likely to be a connector box hidden somewhere which connects the L1 and L2 wires to a switch wire?

I am asking because we want to replace one or both of the switches with a touch-sensitive dimmer. The ones from B&Q come in both 'master' and 'slave' versions and I currently have no idea which I need.

Can anyone help?

Many thanks.

 

[ban-all-sheds]

Can you see which, if any, of the wires are part of the same cable?

 

[stavroshamster]

There is only one cable coming into each box, so all wires connected to the terminals come from the same cable.

 

[Johnmelad502]

There is only one cable coming into each box, so all wires connected to the terminals come from the same cable.

Any chance pf a picture?

 

[RF Lighting]

It sounds like someone has used the cable saving method.

Both three cores will be jointed to one another, and also the live and switch live somewhere.

It will most likely be at a junction box, but it may be at the fitting if you are lucky.

You will be able to adapt the wiring to accomodate a master / slave switch with some testing of the circuit to work out which way it has been connected. (There are two ways which it could have been done, and both will require different connections for the new setup)

 

[stavroshamster]

Thanks for the help.

I have done a bit more searching and found this wiring diagram, which could be the set-up we have:

http://www.diydata.com/planning/twowaylight/twoway.jpg

If this is the case how should the master/slave dimmers be wired up/adapted?

 

[RF Lighting]

It might be, but the live / switched live might be connected across the strappers, and the common intact.

You will have to do some testing with your multimeter before we can say how the new switch needs to be wired.

 

[stavroshamster]

Looks like a multimeter is on my Christmas list then...

What do I need to test when I have one?

 

[ban-all-sheds]

However, from wiring diagrams I have found online I was expecting a switch wire coming out of the L1 and L2 terminals of a 'master' switch with the other switch acting as a 'slave' - this is clearly not the case...

Is our setup an alternative way of wiring up the circuit, or is there likely to be a connector box hidden somewhere which connects the L1 and L2 wires to a switch wire?

Try the diagram of the cable saving method in the wiki: //www.diynot.com/wiki/electrics:two-way-lighting.

 

[stavroshamster]

Thanks for the link.

One question: If I only have one dimmer switch and keep a rocker switch, does it matter which switch I use as the dimmer switch??

And presumably if it doesn't then I need a 'master' type dimmer?

 

[333rocky333]

the dimmer can be either end.

EDIT. As TTC added you will need a normal 2 way dimmer to do this, not the ones with a SLAVE terminal on them

It must also be compatible with the light your dimming though

 

[Taylortwocities]

Be careful. Some touch dimmers (Varilight/Crabtree) do not work with a dimmer at one end and a switch at the other.
They only work with a master dimmer at one end and a slave dimmer at the other.

What is the make/mdoel of the dimmer you have?

 

[stavroshamster]

Right, I have got myself one Varilight Touch Intelligent Master and one Slave Switch

Instructions are here:
http://www.varilight.co.uk/Pages/pdf Touch Remote Dimmer.pdf

I have used a multimeter to test the voltage from each terminal on both the current switches when the lights are off by connecting the black lead to Earth and the red lead to each terminal.

In one of the switches the COM (red) and L2 (blue) terminals read about 235V, whereas the L1 terminal (yellow) reads about 15V.

In the other switch the L2 terminal reads 235V whereas the COM and L1 terminals read about 15V

Am I right in thinking the first switch is the 'master'? And the COM and L2 terminals connect to the LIVE and NEUTRAL? How can I tell which is which?

 

[ban-all-sheds]

Am I right in thinking the first switch is the 'master'?

No.

You've posted a diagram of a possible arrangement, and you've been shown another one in the Wiki - neither has what might be termed a "master" switch - you will need to rewire.

And the COM and L2 terminals connect to the LIVE and NEUTRAL?

The fact that you think you might be able to connect live and neutral to a single pole switch shows a very worrying lack of the most basic understanding of electrical circuits, and the fact that you think that one of your cores is a neutral shows that either you have not bothered to study any of the information you've been given or you don't have a clue what it means.

Whichever it is I don't think you should be carrying on with a job which is going to require you to rewire a lighting circuit based on a genuine understanding of how it works until you have such an understanding.

Either:

1) Replace the switches as they were, and put off rewiring and changing them until you've spent some time going through these:

• //www.diynot.com/wiki/electrics
• //www.diynot.com/forums/viewtopic.php?p=75416#75416
• http://web.archive.org/web/20080213151445/http://www.kevinboone.com/electricity.html
• http://web.archive.org/web/20080213151445/http://www.kevinboone.com/domesticinstallations.html
• //www.diynot.com/forums/viewtopic.php?t=7553[/list]
  
  or
  
  2) Get an electrician in.

 

[BazBee]

Bear with me as I will take it in stages as I try to think it through.
Look at the wiki as posted above at 8.30 on Sunday. No I don't think you have the cable saving circuit, stay at the top of the page.
The first circuit is not what you've got but it shows the live coming into one switch and out at the other. This is the electronics engineers way of wiring a two way and is the reason many books show the red going to the com terminal.
House wiring is normally done a different way just because it is easier to wire.
Underneath the first diagram is another which is how a house gets wired with the two switches connected by 3 cores and the live coming in and out of one switch suing the L1 and L2 terminals. This 'in and out' can then be done with normal twin cable. Did you find this in one of the switches - not mentioned in your earlier posts but you need to make that one your 'master'.
The key thing in this diagram is way the switches get wired com to com, L1 to L1 etc. makes it hard to go wrong. And the colours don't then matter bearing in mind that ALL wires in switches have to be treated as live or potentially live. (really pointless using little red sleeves to mark them)
Now looking at the instruction sheet you linked to you see a circuit diagram that is just like the one on the wiki (but mirror image) showing ceiling rose, master and slaves. So if you have located the switch with the twin I mentioned above you should be home and dry.
If either switch has a single, or a twin with only one wire connected ie being used as a single then STOP - it is not wired as per diagram.