new to dimmer switch

[airfix]

I have purchased a dimmer switch ( metal) in the lounge their are two lights on the ceiling and one switch on the wall.
after removing the plastic switch cover plate I see 2 x red wires going into the switch ( L1 way + Com ) 2 black wires that come from the wall into a chocolate block connector both going into the same connection. an earth travels from the wall to a screw on the metal back box.

 

[Chri5]

And your question is

Swap wires like for like on the L1 and Com of the dimmer, leave the wires on the seperate connector alone and because you have a metal f/plate I'd run a bit of earth wire between the back box earth stud and the f/plate earth terminal.

The f/plate does pick up an earth via the screws for holding the f/plate in (since they screw into the back box lugs) but a link is an added good practice.

 

[airfix]

And your question is

Swap wires like for like on the L1 and Com of the dimmer, leave the wires on the seperate connector alone and because you have a metal f/plate I'd run a bit of earth wire between the back box earth stud and the f/plate earth terminal.

The f/plate does pick up an earth via the screws for holding the f/plate in (since they screw into the back box lugs) but a link is an added good practice.

so just so I am sure, the pic on dimmer switch of a wiggle and an arrow thru it is the common ? and the L1 is a seperate connection

Sorry for sounding daft

 

[ltheb]

Yes... the red wire is the live supply which is made or broken by the switch, so the 'common' is the live feed and L1 returns power to the light fitting.
The black wires in the connector block, on this occasions are 'neutral', in other words the installer brought a live, neutral and earth via the switch to the light fitting.
This should not be confused with a simple 'switch wire' arrangement where the live only is brought down from the ceiling rose, hopefully using the red (or now, brown) wire to the switch, then back up to the light fitting using the black (or blue). This is now a 'live' conductor and therefore should be sleeved or identified as such with red(brown) sleeving or tape.

 

[airfix]

After fitting as discussed the dimmer now buzzes.......!!

 

[jj4091]

Dimmers can buzz slightly, if it is working ok then I wouldn't worry about it, if it is really bad then it may be faulty in which case take it back to where you bought it.