Double Dimmer Wiring Ceiling Dims Fine but Wall Lights Stay on


Postby JimmyHulme1980 » Sun Jan 31, 2016 2:12 pm

Apologies if this is already covered. I have been looking but am still unsure.

I have a dimmable ceiling and two wall light that are also dimmable. Bulbs are the ones they came with. On a standard double switch all was fine. On the double dimmer (which is led compatable) the ceiling light works fine and dims. The wall lights just stay on.

So the wiring I have 1 red cable going into C and a black cable going into L2 on left hand side (Celing light), i then have a brown loop cable going to C on the right side and another red cable going into the C, i then have another black cable going to L2.

Is that loop cable the problem?
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Postby ericmark » Tue Feb 02, 2016 2:27 pm

C stands for common and taking line into the common is normal with on/off lighting switches i.e. not two way. So linking the C's together should not be a problem.
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Postby JimmyHulme1980 » Thu Feb 04, 2016 8:34 am

Cheers EricMark. So if the common loop cable is correct and the left hand side (ceiling lights) is functioning as expected and but the right side (wall lights) is remaining switched on regardless, would that suggest the neutral cables are wrong? Only thing i could do is take left neutral to right side and right to left.

I am also tempted to just get a plastic cheap double switch and mirror the connections just to confirm the dimmer or wall lights are not the problem.
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Postby ericmark » Thu Feb 04, 2016 1:05 pm

[quote]would that suggest the neutral cables are wrong? Only thing i could do is take left neutral to right side and right to left.[/quote]
What neutral cables? It is very unusual to take a neutral to a light switch. Most dimming switches even in the off allow a small amount of current to flow to operate the electronics, this does cause problems with LED lamps.

There is no longer a one diagram fits all for dimming switches, some two way switches have a data wire which is not at 230 volt, some use RF, some do have neutral connections, it is important to follow the wiring for your switch rather than some general wiring diagram.

A non dimming switch has two to four connections for each switch, With many switches they use a common pressing and they just leave out bits not required.

So standard marking would be Com, L1 and L2 but some manufacturers use L1, L2 and L3 where L1 is same as Com. As an electrician I tend to use my meter to find out what the connections are.

There are some specials with 4 connections, these could be double pole or they could be change over switches called an intermediate switch. I would hope your not referring to one of these?

With dimming switches we often have slave and master and it is important they are correctly located.

Where twin and earth or triple and earth cables are used with all cores at 230 volt i.e. no neutral there should be brown (red for old cables) sleeves on the cores but these often fall off or are never put on.

I have found putting a photo or link on this site is a problem. Mainly as you can't see if it worked until passed by sysop but there are other sites much more user friendly. I would try posting pictures as they will make it so much easier.
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Postby JimmyHulme1980 » Fri Feb 05, 2016 9:05 am

Hi EricMark.

I only have 4 cables, the Green/Yellow are earthed to the box so i am left with 2 red and 2 black and the loop brown cable. When i say neutral i mean the black cables. There are two flex cables. I have a red wire going to C and the black cable (From the same flex cable) goes to L2 on the left dimmer and all works fine. Brown loop cable from left C to right C and then basically the same connections on the right hand side from the second flex cable. I will post a pic of wiring and dimmer tomorrow morning.

Cheers
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Postby ericmark » Fri Feb 05, 2016 2:59 pm

The red and black for ceiling lamps is clearly correct. So looking at the other two wires.

One would assume one feeds the wall lamps. However if a link is required one wonders what the other wire is for?

Either there should be no link, or only one of the wires to wall lamp should be connected. Unless you have missed something.

I have seen wall lamps with local switches and the lamps could either be controlled by local switch or wall switch but chances are one of the wires used for wall lamps is not required.

With a ceiling lamp the ceiling rose doubles as a junction box, with wall lights there is no standard way to wire. Often the switch back box is used as a junction box and the neutral although not connected to switch passes through the box. However you don't have enough cables to do that.

Wiring as with ceiling lamps to wall first and then to switch you would not require the link.

So has some one not understood how lights are wired and thought they could get a neutral at the switch?

Since you can't now see how switch was wired you will need to look at a wall lamps and see how that is wired. Is there two cables or just one. And are both the blacks connected together if there are two cables or is the black not connected?

Until you know what the black wire is trial and error could blow the dimmer unit. You could just try removing the link and see if they work.

The other option is two way switching. It is rather naughty but there is a way to operate a second switch using only twin and earth instead of triple and earth however it tends to transmit mains hum onto radio etc so although not banned it is not recommended.

Of the three wires between the two switches one is always live (should call it line) so by borrowing a line from an adjacent switch they can dispense with one cable.

Now with two way wiring L1 and L2 connect to line feed and line to lamp and the com connection only connects switch to switch. The two ends of the wire are connected like for like between the two switches.

So with two way switching the red and black would go to com and L1 or L2 and the link wire would go to which ever one of L1 and L2 is not being used.

What is very important is the correct wire goes to com, so if two way switched then look at the other switch of the pair and see colour of wire into com and use same colour in com with slave switch. If L1 and L2 are swapped then switch works wrong way around but still works. It is wire to come which is important.

However your post did not say it has two way switching.
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