Installing dimmer switch - another question about wiring

[4hero]

Hi folks,

After successfully fitting the dimmer yesterday (with your help), I have another question about fitting another dimmer (in the kitchen this time). I would like to replace a double switch with a dimmer.

This is the existing switch, the switch on the right is no longer used (it was for an extractor in the ceiling, which has been removed, but wiring is still in place), and the left is for the lights.


The back side of the switch.



And the new dimmer:



Can you tell me which wires from the switch should go into where on the dimmer please?

Any help would be superb! Thanks in advance,

Neil.

[TooLateForAName]

My guess would be that the wires into Acom and Bcom and the link between those are the lighting ring live cables with the A1 and B1 being the runs out to the bulb and the fan.

On that basis you would combine the wires into Acom and Bcom and have both going to a single common on your dimmer switch. The live out to the light(B1?) goes to your L1 and the other live is redundant as the fan has gone.

Edited by TooLateForAName on Friday 21st August 19:36

[Raverbaby]

Take the loop between ACOM and BCOM out and put your remaining 2 cables in to your COM of the dimmer. (this is the terminal with the wee squigley line)
Put A1 in to a bit of connector block ( this will be the fan cable thats not in use) and just let it sit in the back box.
Put B1 in to the L1 of your dimmer.

Job Done!


Edit - beaten to it, What he said ^^^^^^

Edited by Raverbaby on Friday 21st August 19:39

[miniman]

TooLateForAName said:

My guess would be that the wires into Acom and Bcom are the lighting ring live cable with the A and B being the runs out to the bulb and the fan.

On that basis you would combine the wires into Acom and Bcom and have both going to a single common on your dimmer switch. The live out to the light goes to your L1 and the other live is redundant as the fan has gone.

Agreed, the Acom and Bcom are the live ring main so you need to get rid of the small piece of connecting wire between the two, and then join them together. You also need to identify which of the other wires (A or B) goes to the light. Then Acom + Bcom goes into L1 on the dimmer, and whichever of A and B goes to the light go into X / squiggly line.

ETA too slow! I would go with the live loop going into L1 but as per my post yesterday it is AC anyway so no great shakes which way round it goes.

Edited by miniman on Friday 21st August 19:40

[netherfield]

Discard link wire from ACOM to BCOM
Place two remaining wires at ACOM and BCOM in to L1 on dimmer switch
place wire from B1 to x on dimmer switch
wire from A1 - either snip off or tape up and leave in the back box,just be sure this wire does not touch any terminal when screwing new switch in place

Make sure front plate on dimmer switch is earthed.

[Ganglandboss]

miniman said:

it is AC anyway so no great shakes which way round it goes.

Polarity is not an is not an issue as there should not be a neutral at the switch but the fact it is AC doesn't make a difference; polarity in mains circuits is very important.

[netherfield]

It is good practice to put the load on to the x terminal,then it does not matter if the switch is used as a one way or two way device.

[4hero]

Thanks folks, will give this a go this morning.

netherfield said:

Discard link wire from ACOM to BCOM
Place two remaining wires at ACOM and BCOM in to L1 on dimmer switch
place wire from B1 to x on dimmer switch
wire from A1 - either snip off or tape up and leave in the back box,just be sure this wire does not touch any terminal when screwing new switch in place

Make sure front plate on dimmer switch is earthed.

You seemto be saying the opposite to what others are saying I should do?

[TooLateForAName]

I am not an electrician, but this is my understanding, GLB or someone will give a better explanation.

In the case of a simple switch it doesn't actually matter which end of the switch the wires go to. You are using these switches as simple one way switches, although they are capable of being two way switches.

______ \______&   simple one way switch  to bulb (&)  
You can see that it doesnt really matter which way around the switch goes.  

 ____/ ____  or ____ \_____  Think of the switch hinge as being COM

         ____________
_______/ ____________ \__________&  

2x two way switch allowing you to have two points of control of the light. You see that depending on the switch position the Com terminal can be connected to two popitions L1 / L2. Two switches may be used for example at the top and bottom of stairs to give a dual point of control. When both switches are at the same position the circuit is complete.

Now all of these are likely to be fed from a ring circuit - a loop around the house - hence there will be one terminal of the switch which has two wires - the ring.

eg ring showing two light switches - in effect what you had in a single physical unit. Ring comes into Acom, little link to BCom and off to the next thing on the ring. Cables out of AL1 and BL1 to the light and the fan.
|
|
|
+--/ ---o---&
|
|
+--/ ----o--&
|

The + being the terminal with two wires and the o being the other terminal on the switch. Sometimes the wiring can be rather more complex with the ring passing through the light rose itself, but for your purposes you seem to have the simple switches as shown. Another alternative is to have a connection box on the ring and a single wire then going through the switch and on to the light.

In this circumstance, all the wires that you are looking at are (potentially) live. The comment about things not mattering because it is AC is, as GanglandBoss has suggested, potentially misleading and dangerous.

The neutral wire can be thought of as the circuit earth. Electricity flows from the live wire, through the load (light in this case) to the neutral (which goes back to the power station and earths there. What is called the Earth wire is more correctly a circuit protective conductor and is there to take electric to earth from things like the switch cover in the event of a fault (and as a consequence cause the trip switch to go)

Making sure that any spare wires cannot touch anything is important (insulation tape/choc connector/whatever) as is connecting earth/cpc to the switch face and/or metal back box.

Edited by TooLateForAName on Saturday 22 August 09:48 to sort formatting which was all over the place.

Edited by TooLateForAName on Saturday 22 August 13:52

[Ganglandboss]

TooLateForAName said:

I am not an electrician, but this is my understanding, GLB or someone will give a better explanation.

I generally don't like to explain stuff like this as is is easy to misinterpret text and I also feel that if you need to ask, you shouldn't be doing it yourself. The first two responses are correct but as someone added, make sure the switch-plate is earthed.

[TooLateForAName]

Fair enough.

[4hero]

Thanks for all the help.

Ganglandboss said:

TooLateForAName said:

I am not an electrician, but this is my understanding, GLB or someone will give a better explanation.

I generally don't like to explain stuff like this as is is easy to misinterpret text and I also feel that if you need to ask, you shouldn't be doing it yourself. The first two responses are correct but as someone added, make sure the switch-plate is earthed.

I followed the first two answers and all is working well, the plate is also earthed.

Thanks again,

Neil.