Replace one-gang with two gang

[MrOrange]

Hi,
My existing one-way one-gang light switch has 2 red wires leading into L1 and one red wire leading into L2. L3 is not being used. It also has 2 black common wires which are joined.
I'd like to replace it with a dimmer and I have two questions: First, if I want to change to a one-way one-gang dimmer, do I set it up the same (i.e. 2 reds into L1, 1 red into L2) or do I have to use the C? Second, is it possible to change this to a two-gang dimmer (for the two lights in my room) and if so what goes where?

Really appreciate your help!

 

[Adam_151]

Its a slightly different way of labeling it,

Com on the new switch is equal to L1 on the old switch
L1 on the new switch is equal to L2 on the old switch
L2 on the new switch is equal to L3 on the old switch

Though I should imagine the groups of wires are the wrong way round, i'm assuming that each one goes to a separate light fitting*, to test this, temporarily disconnect one and check that one light stops working, but the other one continues to work, if this is so then the two wires together should really go into L1 (L2 on the old switch) and the single one into com (L1 on the old switch).

As for two dimmers, providing it has been verified that it is wired as above, then the wire on its own goes to both commons (use a link wire) and the other wires go one to the L1 on each dimmer

*its also possible that the lighting circuit is just looped in at the switch instead, and that means you haven't got a separate feed for each light at the switch, and it'd be substantually harder to split them onto two switches

 

[MrOrange]

Thanks Adam - that info was spot on.