Newbie trying to swap double switch for double dimmer - HELP!!

[jfb1977]

Hi everyone,

Go easy on me, I'm a newbie to the forum and have got myself in a bit of a pickle.

We're doing up our basement.

The basement has a single light switch at the top of the stairs that controls two bulbs - one at the top of the stairs (where the single switch is) and one under the stairs.

At the bottom of the stairs is a double switch. One controls the same two bulbs as the single switch at the top of the stairs, the other controls 6 flush ceiling mounted spots only.

We wanted to swap out the 2 gang switch at the bottom of the stairs for a 2 gang dimmer (leaving the single gang switch at the top of the stairs as is).

I've done this kind of thing before, and whilst FAARRR from being an expert it's usually been pretty simple, a case of moving wires from like for like connections usually.

However, this is NOT the case in this house.

Here's how the double switch at the bottom of the stairs was wired in when I took it off -

Now that it's all disconnect I can see that I have 4 cables running to the box - all with different (it would seem) core wires!

These are the 4 -

Cable 1. Unlabelled, but I believe this is for the spots. Seems to be 4 core - Red (live), Blue (neutral) Yellow (?) and the yellow and green (earth)

Cable 2. (Labelled 'down' - so assume under stairs light).

3 core - simple - Brown (live), Blue (neutral) and an earth. Incidentally all 4 earth cables just run into a single terminal block...does that seem right?!

Cable 3.
(Labelled 'landing' - so obviously the upstairs light by the single switch at the top of the stairs).

3 core - simple - Brown (live), Blue (neutral) running to the same terminal in a connector block with the black wire from cable 4 (labelled feed - see below) and an earth (running to that connector block).

Cable 4. Labelled 'feed'.

3 Core - Red (live), Black (neutral) running to connector block with blue with from cable 3 (Landing) and earth running to connector block with the other 3 earth wires.

So I have a pretty good idea of what everything IS....but I have absolutely ZERO idea what goes where when I look at the back of this 2 way, 2 gang dimmer.....was expecting to see L1, L2 etc.....

Apologies for the long post, but wanted to give as much info as possible.

If someone can tell me what goes where (in language a toddler would understand then hopefully I've got half a chance of being able to sort this!

Thanks so much in advance....so glad to have found this forum, think I may be posting a lot....I have a lot of great ideas....but not so much skill or experience!

 

[EFLImpudence]

Is there a diagram in the dimmer instructions for a two-way system (two switches for one light or group of lights), or

what is the make and model of the dimmer?

 

[SUNRAY]

The problem you have is the new dimmer has a single common terminal and the method of wiring the 2 way pair will have to change.

I'll sketch what I believe you have and come back in a short while.

One important thing, the metal front plate will have to be earthed.

 

[SUNRAY]

Is there a diagram in the dimmer instructions for a two-way system (two switches for one light or group of lights), or

what is the make and model of the dimmer?

LAP with single common.

 

[whall3y]

Looks like a LAP - https://www.screwfix.com/p/lap-1-gang-2-way-dimmer-switch-slate-effect/4878g The "L" is the single common, the others are L1, L2 for the respective switch?

 

[jfb1977]

Is there a diagram in the dimmer instructions for a two-way system (two switches for one light or group of lights), or

what is the make and model of the dimmer?

It came from B&Q (don't judge me, it's 30 seconds over the road and this was obviously going to be a 'quick' job) - it's a 2 Gang, 2 Way Dimmer made by a company called Holder. No instructions in the box annoyingly.

 

[SUNRAY]

Does the single switch just have cable 1 connected?

 

[jfb1977]

The problem you have is the new dimmer has a single common terminal and the method of wiring the 2 way pair will have to change.

I'll sketch what I believe you have and come back in a short while.

One important thing, the metal front plate will have to be earthed.

Amazing! Thank you.

Two things. One thing that may be mighty important....

1) I've just realised that I THINK the blue neutral from what I'm calling cable 2 "down" had actually snapped - I think originally it ran to the connector block with the neutral wire from the landing...which would make sense to me....

2) Can I earth the front plate by simply running a wire from the unused connection from the connector box that all 4 earths currently feed in to, to the earth terminal on the back of the face plate? Would that work?

 

[jfb1977]

Does the single switch just have cable 1 connected?

Yes. (I think).

This is the wiring into the single switch at the top of the stairs...

 

[jfb1977]

This is the wire I believe has snapped / broken....would you agree @SUNRAY?

 

[SUNRAY]

Yes. (I think).

This is the wiring into the single switch at the top of the stairs...

View attachment 209121 View attachment 209122

Perfect.
This is my interpretation of your existing set-up, ingoring earth wires for clarity and using your cable numbers:

Assuming you are happy that I have the interpreted your description correctly, my suggestion follows, you will require another single connector block [shown purple]

Your existing short red link wire is not required.
A link from the connector blockwith all the earths to the front plate is perfect.

I have also assumed the same as yourself regarding the broken blue.

 

[SUNRAY]

No changes required in the single switch, just in the double.

Good luck, let us know.

 

[jfb1977]

Perfect.
This is my interpretation of your existing set-up, ingoring earth wires for clarity and using your cable numbers:
View attachment 209128
Assuming you are happy that I have the interpreted your description correctly, my suggestion follows, you will require another single connector block [shown purple]
View attachment 209130
Your existing short red link wire is not required.
A link from the connector blockwith all the earths to the front plate is perfect.

I have also assumed the same as yourself regarding the broken blue.

I think you've most likely nailed this and thank you SO much for taking the time, it's extremely kind of you and I really do appreciate it.

One last dumb question if I may (!) - I assume that what's marked as "C" on your wiring diagram is the connection marked L on the back of the dimmer.

Again, thanks SO much. I'll let you know how I get on.

 

[SUNRAY]

I think you've most likely nailed this and thank you SO much for taking the time, it's extremely kind of you and I really do appreciate it.

One last dumb question if I may (!) - I assume that what's marked as "C" on your wiring diagram is the connection marked L on the back of the dimmer.

Again, thanks SO much. I'll let you know how I get on.

Yes correct, apologies.

 

[jfb1977]

So....sit rep.

Close, but no cigar. By which I mean when I first wired it in, the landing light flickered (I assume probably because it has an non dimmable LED bulb in it). Weirdly it seemed to flicker less when I turned the dimmer down slightly, but now I can't get it to do anything - so there was power going to it. Annoyingly I don't have any standard halogen bulbs in the house, so can't do much more testing tonight.

But no joy on the spots - but I can hear them buzzing when I flick the fuse on...just no light. They say they're dimmable. So again, seems there's power getting to them, but alas no light.

To follow photos of my wiring (so you can check my homework) and the spots - I've got a feeling the wiring might be right, but maybe the spec of the dimmer and / or spots are incompatible for some reason?

I've now numbered the cables as per all of the above chat.

1 = Spots

2 = Down (understairs)

3 = Landing

4 = Feed

Wired in as per your diagram which I read as -

Cable 1 - Red and blue wires to dimmer terminals as pictured, yellow wire connected via a block to brown wire on cable 2.
Cable 2 - Brown wire connected via block to yellow from cable 1, blue to terminal block (with black from cable 4 and blue from cable 3).
Cable 3 - Brown wire to dimmer terminal as shown, blue to terminal block (with black from 4 and blue from 2).
Cable 4 - Red to C (marked as L), black to terminal block (with blue from 2 and blue from 3).

I've run a wire from the connector holding the 4 earths to the earth terminal on the face plate (currently the wire is black as that's the only colour I had but I'll replace with yellow and green when I can get some tomorrow).

So....my wiring -

And a few detail shots of the spots I'm trying to run....

Any ideas? Any common mistakes that amateurs like me tend to make? Have I bought the wrong dimmer? Any wires I should double check based on the above?

Thanks again....I feel like I'm close....just something isn't quite right.