Dimmer switch with 2 red wires & earth

[SRJDIY]

I have a dimmer switch that recently stopped working, so I'm hoping to replace it with a new one.

This is the only switch that controls the light in question, so based on my googling I expected to see one red or brown live wire and one black or blue switched live wire going into the switch. However, both wires going in are red.

My understanding is that I need to attach the live wire to common and the switched live to L1 on the new switch, but I'm not sure how to do this as I'm not sure if both red wires are live or if only one is and the other's been mislabelled.

Adding to the confusion, the label on the old switch says 'connect either way around', but one terminal has a red dot underneath it and the other doesn't, suggesting there is a difference.

Does anyone know what's going on please? Is this something with a simple answer I just don't know, or is it time to call an electrician in?

I've also attached a picture if it helps. The label says "Connect wires either way around, 1 way 250w, 200-250v, suppressed to BS800, Pats 1514161 & 2063573''.

Thank you!

[Someone-Else]

You can never go by the colours, since it always depends on how who ever installed it, chose to do it.
Normal twin and earth does have (as you say) Brown and blue OR Black and red. In either case the switched wire should be marked as such, so Brown sleeving on the blue wire OR red sleeving on the black wire. BUT who ever wired your house actually used the correct cable. You really should use twin red (Twin brown from 2004) for the cable to the light switch.

To answer your question, it does not matter which way round you connect your new light switch.

[arco_iris]

"Connect either way round" means that, it doesn't matter which wire goes to which terminal.

(In this case - there may be circumstances when it could matter, but not here).

The switch point has been wired with two reds (equivalent modern installations in last 18-20 years would be two browns) so that Switched Live is the correct colour when it gets to the lamp. Whoever installed it originally exhibited good practice - black+red or brown+blue, though acceptable (especially if a sleeve is used) is really a cheat using standard, conventional cable.

S-E was typing faster than me!

[SRJDIY]

To answer your question, it does not matter which way round you connect your new light switch.

"Connect either way round" means that, it doesn't matter which wire goes to which terminal.

(In this case - there may be circumstances when it could matter, but not here).

Thanks for the responses! I'm still curious though. I understand the logic of having the switched live wire be red because it can be live if the switch is on. But if it doesn't matter which wire I connect to common and which to L1 then why is this please? Sorry to be a pain; I just want to make sure I fully understand what's actually happening when I wire the new switch up!

[Someone-Else]

It's the way the switch is designed.