L3 is marked as common on my dimmer switch, so why is permanent live attached to L1?

[Jazzy]

Evening

I'd be grateful if someone could shed a bit of light on this please!

I have a 2 gang dimmer light switch (that has a push on/off knob) that I’m replacing with a standard 2 gang 1 way switch (well, it’s actually a 2 gang 2 way, but can be used as 1 way) - I’ve replaced switches before, but the wiring in this new (but old, so has pre-2006 wiring colour scheme) house is causing me to scratch my head! Essentially I’m a bit confused as to why permanent live is connected to L1, when L3 appears to be designated as the common. Presumably this has just reversed the state of the knob i.e. off is on and vice versa?

Basically there 2 sets of cables coming in controlling 2 different pairs of light fittings:

• Cable on right goes to left gang which controls pair of wall-mounted lights
• Cable on left goes to right gang which controls pair of ceiling-mounted lights

The cable feeding into the right gang has a red wire (R1), a black wire (I unnecessarily labelled that in the 1st image...) and an earth, and the left gang cable has a red (R2) and an earth. There is also a red loop (R1-2) connecting the 2 gangs, and both earths are connected to the box.

R1 = Permanent live
R2 = Switched live to wall-mounted lights
Black = Switched live to ceiling mounted lights

The new light switch has L1, L2 and L3 (it’s made by Crabtree) - my understanding is that permanent live (i.e. R1) would to go to L1 on the 1st gang, a loop would connect both L1s, R2 would go to L2 on the 1st gang, and the black would go to L2 on the 2nd gang.

Is there any particular reason as to why the original switch would have permanent live on L1 instead of being connected to the designated common?

Ta

 

[steptoe]

On 1 way switches it's irrelevant what wire is in which terminal , really.
If you want to be pedantic/perfect , then on your new switch,
Put the permanent Live into common (L1) and link the 2 commons (L1s), and put your switch wires into the two L2 terminals.


EDIT : it will work exactly the same if you put the permanent Live into L2 (or L3) and link both L2s (or L3s) together and use L1 for your switch wires

 

[ProDave]

There is a good argument on a 1 way switch to put permanent live into L1 and switched L out from common. That way with the switch off, no other terminal is L.

If you put permanent L to common then when the switch is off, the unused terminal L2 is live.

 

[SPECIAL LOCATION]

There is a good argument on a 1 way switch to put permanent live into L1 and switched L out from common. That way with the switch off, no other terminal is L.

If you put permanent L to common then when the switch is off, the unused terminal L2 is live.

Think you mean on a 2-way switch..

as a 1way switch only has two possible terminals to connect onto...

 

[ProDave]

Think you mean on a 2-way switch..

as a 1way switch only has two possible terminals to connect onto...

I mean when using a 2 way switch in a 1 way on / off application.

 

[Fleeting]

There is a good argument on a 1 way switch to put permanent live into L1 and switched L out from common. That way with the switch off, no other terminal is L.

If you put permanent L to common then when the switch is off, the unused terminal L2 is live.

Which good argument would that be because I say why does it matter.

 

[kerching]

Well I think they should scrap making 1 ways and 2 ways and just make intermediates. But that's just me

 

[SPECIAL LOCATION]

Well I think they should scrap making 1 ways and 2 ways and just make intermediates. But that's just me

But then that is just using common sense...

and someone like yourself who is relatively new to the game may not fully understand the wisdom of the decision makers!

 

[kerching]

Yes indeed I have much to learn. I can only dream of being elevated to the halcyon state of some of the esteemed members on here. Ultimately being "asked to teach" would be a final goal as I feel having my own YouTube channel would just be a step too far

 

[binky]

Well I think they should scrap making 1 ways and 2 ways and just make intermediates. But that's just me

Can't do that, I would have to think about how to wire it....

 

[steptoe]

Can't do that, I would have to think about how to wire it....

You could ask someone that's been asked to teach

 

[SPECIAL LOCATION]

Can't do that, I would have to think about how to wire it....

You could ask someone that's been asked to teach

Or just watch a 45min Youtube video on how to wire an intermediate light switch for every application...

 

[Jazzy]

There is a good argument on a 1 way switch to put permanent live into L1 and switched L out from common. That way with the switch off, no other terminal is L.

If you put permanent L to common then when the switch is off, the unused terminal L2 is live.

Thanks all

Hadn't even considered that - so this is how the current dimmer has been wired up then. It does seem 'safer', however if that is the case then why is it not a standard?