In my sitting room I have two lights on the ceiling, each with three bulbs in. On the wall is a two button dimmer switch (press each knob to turn on lights, rotate knobs to dim)

A while ago the dimmer part stopped working, so today I bought a new dimmer switch - looks exactly the same;



Unscrewed the wall plate and inside were 4 wires - 2 red, 2 black (with red sleeve). The red wires went into L1 (one into L1 on each black plastic bit) and the black wires went into the what looks to be marked as ground (?)

Well after swapping the swithc over I turned the lighting ring back on and one of the lights now flickers, and although the dimmer works, it's so dim at "full bright" it's useless, and the other one doesn't flicker, is just as dim, and buzzes a bit from the switch. So I swapped the switch over again to the original, which works at proper brightness, no flickering, but the dimmer is broken (as before)

Any idea's whats wrong?

 

What size are the bulbs ? Are they fed from a transformer ?

 

I don't know

The only difference I can see in the two light switches are;

Original says 40-250w, new one says 60-250w
Original has a "C" (could be a "G") marked where the black wire went, new one has a funy, wavy arrow design where the black wire goes. Both have L1 and L2 next to each other.

Both have a brass thing saying the chassis must be earthed to it, but the wiring in the wall has the two yellow/green earth wires disappearing up into the cable spur...

 

c=common
fully arrow= earth lol

 

Well on the original switch it had three connections on each of the black plastic bits - L1, L2 and C, and red wire went into L1 and black wire went into C

On the new one each black plastic bit has L1, L2 and the funny arrow bit, so I wired up like the original - reds in each L1, blacks into each "funny arrow", and got "funny" results lol.... IE, the flickering, really dim/low power....

I reckon the actual ceiling light units are fucked aswell, as when (ages ago) the dimmers stopped working on the original switch, there was a "POP" noise and the lights went out (tripped the ground floor light ring on the breaker board) and after turning back on the dimmers didn't work. However, it's done it several times, and now only one of the three light "sockets" in each light unit work. Put a new bulb into the other two sockets and they don't work. So each light unit has only one working light socket and no dimming.

 

Ok, the total wattage for the new dimmer must be 60 watts or more per dimmer, if not it will cause problems.
Also, if the lights are low voltage and use a transformer, this too can cause issues on some dimmer types.


Also, as another point apart from your current issues....
I presume your old dimmer was a NON metal face plate and the new one is metal.
If this is the case, you will need a proper earth connection installed.
Dont assume the earth wires you have are earths as they will need proper testing.

 

Simon - both units are metal - they are exactly the same, and both from B+Q. The only difference is it looks like at some point B+Q changed the black plastic bit on the back...

Also, I think the bulbs are 40w (I'll check in a mo) so if only one was working in each light unit, then each switch will only be getting 40w load, and the new switch wants min of 60w load, so would that be causing the problems with very dim lights and flickering/buzzing?

 

Thrush spot on

 

So if I take it back and get one that will run 40-250w it should be okay, and if I can't get one, could I just use 60w bulbs instead of the 40w ones?

I am wiring it up the right way tho aren't I? red to L1, black to the wavy arrow symbol?

And the problem isn't related to the fact that only one light socket in each light unit is working?

 

Yes you are wiring it up correctly.

I would try a 60w bulb first to be sure !

 

The funny arrow or squiggly line thing is your common, which would have been c on your old light switch. This is where your permanent live goes and the switch wire for the light is into L1. Should work alright as long as the lights are 230v and not ones with an inbuilt transformer.

 

The bulbs themselves are just stock screw cap 40w 240v bulbs.....

 

Right, popped back to B+Q and changed it for an idental one, but this time it said min load 40w, max of 250, installed that one and it works perfectly

Last Q - red goes to L1, black to common, and L2 is vacant (was how it was before, and is now)

Inside the wall box where the spur comes in, is a grey cable - 2x red, 2x black and 2x green/yellow earth. Obvisouly red and black go to switch, and the earths are attached to the chassis/wall box.

My switch has a brass/metal screw bot on it saying it must be attached to "earth in terminal box"

But I don't have a wire for this?

Do I just need to fit a bit of electrical wire from the faceplate to the point in the chassis/wall box where the spur earths are attached?

There wasn't one there before, but I have had a couple static electricity shocks (usually if I am wearing my fleece and been lying on the sofa)

 

Yeah do this , usually there'll be a lug on the back of the box for this , better to have the face earthed

 

Yeah the lug has the two green/yellow earth cables from the spur attached to it. So just get a bit of copper wire and attach to the lug on the faceplat and to the lug on the terminal box? And leave the two earth cables, leave these attached aswell?

 

Yeah just get an extra bit of wire outta some T+E get some gr/ye sleeving and attach it from the backbox to the face plate just incase for some reason the plate come live.
edited to say yes you can leave the two other earth cables in the lug on the backbox

 

Thanks

But whats T+E?

 

twin and earth

 

Twin and earth the type of cable used in all domestic installations as said above.
Its not the end of the world if you can't get an extra earth cabe to the plate as it will be earthed through the screws that screw the plate back..... just not good practice