How do I replace a 2 button dimmer switch?

[mungo_55]

Hi, 

Hoping someone can help with this.

I'm trying to replace a 2 knob dimmer switch.  The trouble I'm having is the 

new switch looks a bit different with the connections available to the old switch, and 

the existing wiring looks different to the diagram I'm supposed to use for the new 

switch.

Each knob powers 2 lights.  Knob 1 for 2 wall lights, knob 2 for 2 ceiling lights.

The wall box has 4 red live wires and 4 black neutral wires.  I'm guessing there's 1 pair of cables for each light ?  Only the red cables are connected to the existing dimmer.  All the black wires finish in a plastic terminal connector.  The existing dimmer has a COM and an L2 connector for each knob.  There's 1 red cable to each COM and each L2 connector, but there's also a small separate length of red cable between the two L2 connectors.

I'm surprised none of the black neutral wires are used.

The new dimmer switch has a COM, L1 and L2 connector for each knob.  The wiring diagram seems to say put a black neutral wire into each knobs COM connector and a red live wire into each L1 connector.

So how do I rewire this new switch?  I suspect I need to just use the red live  wires again, but I'm not really sure how !

Any help would be very much appreciated !  (some photos are below)

cheers

Mungo

 

[Manator]

Welcome to the forum.

The black wires if they are connected into a connector will not be used for your switching, more likely to be the neutrals for the circuit.

The red interlinking wire will mean that only one of the red wires coming to the switch will be permanently live. This should be connected between the two COM terminals. Each pair of red cables should go as they were wired in the original switch. The L2 connection is for two way switching so unless there is another switch they are not required.

Make sure you disconnect from mains power before attempting to do any connections. Use a perm marker to mark which cables are which and then just connect to COM and L1 on each dimmer.

 

[ProDave]

.....The wiring diagram seems to say put a black neutral wire into each knobs COM connector and a red live wire into each L1 connector.

No it does NOT say that.

What is is trying to say is L in to L1 and switched L out from COM.  Sometimes with some wiring configurations a black core is used as switched L where it should be sleeved with a bit of red sleeving, it is most certainly NOT a neutral and the instructions don't say that.

As already explained your lights are wired "loop at switch" so the neutral passes through the switch box but is not connected to anything there, just looped together in the terminal block, so in your case the black wires are neutral and don't connect to the switch. You should not need to touch these.

 

[mungo_55]

Thanks a lot for the replies guys, that really helps.

The reason I thought the wiring diagram wanted neutral is that there's a wired marked 'N' going to 'Load' and then into COM.

 

[Doc Hudson]

Thanks a lot for the replies guys, that really helps.

The reason I thought the wiring diagram wanted neutral is that there's a wired marked 'N' going to 'Load' and then into COM.

The wire between the switch and the load is the Switched live. The neutral side is the other side of the load. Its not uncommon for DIY'ers to think that you need a neutral at a switch. But if you just remember the circuit is;  Supply : Permanent Live : Switch : Switched Live : Load(light) : Neutral : Back to Supply. 

Doc H.

 

[mungo_55]

Ah, ok, cheers Doc.

One other question - once I took the wires out of the old dimmer I realised that there wasnt a separate wire running between the two L2 connectors as I said, it was a wire running into the first L2 connector with a section bared, then the same wire running on to the next L2 connector.

So instead of running a wire between the two COM connectors as Manator said I've copied what was there by using this wire to connect to one L1 connector on one button on the new dimmer and then running it on to the L1 on the second button.   The other connections Ive made as suggested above.

Does this sound ok ?. The dimmer seems to work fine, but I just wanted to ask the experts !

(so I've got one red wire going to each of the two COM connectors, one going to each of the two L1 connectors, and one of these carries on from one L1 to the other one)

cheers

Mungo

 

[steptoe]

Yes, just seems as though the original installer uses L1 as the link.instead of the COM, this is completely fine for a 1way switch, totally interchangeable. 

 

[mungo_55]

Thanks for the advice steptoe. Got it all sorted now and nothing's gone bang.