Replacing Dimmer Switch

[SAL T]

Hello lads wanted a bit of advice regarding replacing a broken dimmer switch for a new one.

I know the fuse must be turned off and to check if power is dead. What I'd like to know is regarding the wiring. There are 2 red wires going into the switch and 1 blue. I take it the reds are L1 and L2 and the blue is common? Theres also a green that goes into ground with common and not into the switch? Whats the green for?

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[EFLImpudence]

Where does the other end of the Blue wire go?

 

[RandomGrinch]

Where does the other end of the Blue wire go?

To the metal faceplate?
Hopefully!

 

[Harry Bloomfield]

I know the fuse must be turned off and to check if power is dead. What I'd like to know is regarding the wiring. There are 2 red wires going into the switch and 1 blue. I take it the reds are L1 and L2 and the blue is common? Theres also a green that goes into ground with common and not into the switch? Whats the green for?

Green is the earth, blue has also been used to earth the metal faceplate, though it ought to has been green/yellow.

The two reds are one live and the other the switch wire.