Outcome of attached wiring. 1. Switch at bottom of stair turns lights on and off as it should. 2. Dimmer does nothing. 3. Landing switch does nothing. 4. All other upstairs lighting working as it should.
Would be much appreciated if anybody could point me in the right direction. Thanks
Basic two way wiring first there are two types of switch one called a two way switch the other called an intermediate switch, an intermediate can be used as a two way but not the other way around.
Either end of a two way wiring you have two way switches these are often labelled as com, L1 and L2 but something as L1, L2 and L3 in which case L1 is com.
When used as on/off one wire to com and one to either L1 or L2 but when used as two way the lamp wires go to L1 and L2 and between the two switches all connections go together like for like. With the intermediate switch the com wire does not connect to switch it just has a connector block the other wires are split by the switch and what it does is swap the two wires.
You have two x two way switches and as many intermediate switches as you like.
Now with a dimmer it becomes a problem as the dimmer is only in one location so dimmer normally wired between switch com and the com wire and switch is normally a pull-push switch.
In order to be able to control the dimming from multi locations we have a master and slave dimming switch the master is always where the light switch wire come in. It will still have L1 and L2 but there is a wavy line with arrow through it instead of com. This does not actually carry current it carries digital information from slaves to master. Now you don't have an intermediate switch all slaves are wired the same just three connections.
One of the reasons your lights may not work is you may have a slave master dimmer and are trying to use it with standard system.
Of the three wires that go switch to switch in the non dimmer wiring is always line. Either L1 or L2 never com. By borrowing that line wire from another switch one could use two cores between the two two way switches. This would produce interference on some equipment specially hearing aids was is not often done now, plus you can't use this with intermediate switching.
Looking at your diagram I can't see the intermediate switch this will have 4 connections. It will not be the dimmer you don't get intermediate dimmers. Nothing seems to make sense with bottom switch. And with middle switch should not be two wires to com.
I will guess middle switch is two way and should be intermediate but since can't work out what is happening with bottom switch can't be sure.
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