1-gang rocker → 2-gang dimmer

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Hi there.

Been researching but unable to find any answers. Wondering if what I want to do is even possible.

If it is, could it be done by someone with very little electrical know-how provided they were very dilligent and careful (ahem)?

If not, would it be a fairly simple job for an experienced electrician? I live in an ex-local authority flat, so I’m really hoping there is an answer that is simpler than rewiring the whole place.

The idea/problem:

I’m looking to replace my living room light: a ceiling rose with a single outlet controlled by a standard 1-gang 2-way rocker switch.

I’d like to replace this with a ceiling rose with two outlets controlled by a 2-gang dimmer. The reason for the 2-gang dimmer is because I want to control each lamp coming from the double rose as independent light sources.

This would allow me to have one lamp suspended in the middle of the room on a short flex for standard room illumination, and another lamp, on a longer flex, suspended via a hook above the dining table, for evening meals and working.

Hope this makes sense and thanks in advance for any/all advice. A very rudimentary picture is attached in case it makes it easier to see what I am hoping for.

 
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I live in an ex-local authority flat,

There's a slim chance you may be very lucky and have steel conduit inside the wall, heading to the ceiling rose. If you do, it will simplify your task immensely (i.e. no chiselling out plaster from the wall and no pulling down ceilings and making good)

Turn the power off at the fusebox, unscrew the switch from the wall and show us a picture of what's behind.

Is it a top floor flat which you have access to the loft if there is one?
 
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There's a slim chance you may be very lucky and have steel conduit inside the wall, heading to the ceiling rose. If you do, it will simplify your task immensely (i.e. no chiselling out plaster from the wall and no pulling down ceilings and making good)

Turn the power off at the fusebox, unscrew the switch from the wall and show us a picture of what's behind.

Is it a top floor flat which you have access to the loft if there is one?

Thank you for the reply, rsgaz. This looks like a conduit to me.


On the 3rd floor of a 12 floor block so no going in from above.
 
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Fantastic. That all makes sense.
Thanks for all your help.
 

SFK

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Rsgaz
Happy to be told that I am looking at that image wrong - but my view of that image suggests that there is one live and two switched live cables going to switch (and no earth).
Does he actually need to pull a new switched live cable down the conduit?

If all three wires go to the rose (ie one live and two switched live cables) I would seperate the two switched live cables into the two dimmers and put the live into the first dimmer and loop it into the second dimmer.

Question to Jonny - can you show us an image of the cables at the ceiling rose?

SFK
 
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suggests that there is one live and two switched live cables going to switch (and no earth).

It's more likely that the lives are looped at the switches, not the rose. So I've assumed the two together are both live and the single is switched live.

If all three wires go to the rose

The live in and live out will probably be just 'passing through' the rose, from the previous switch and on to the next switch, there will be no connections or cut ends there. Yes, it could be re-jigged so that one red wire is the live and the other existing two could become the switched lives, but you'd need extra slack at the rose to cut the existing reds that pass through, so it's just easier to run an extra wire as he has conduit, less things to have to alter for a DIYer.

Good point about the earth. OP, unless you can check that the back box has been earthed by the conduit using a multimeter, then you'll have to fit a plastic switch. It seems your existing switch is metal, but that's no guarantee.
 
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SFK

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Jonny, one last suggestion from me,
- if you do not want to pull a new cable, you could put a "Switched BC Cord Grip Lamp Holder" on the end of the cable above the dining table.
Both lamps will come on when you use a single dimmer, but you could turn the dining table lamp on and off (when room light is on) when needed.
Noted that this might is not the solution you are looking for - but a bit of a keep it simple solution.

https://cpc.farnell.com/pro-elec/9489-t2/switched-lampholder-bc/dp/PL09245

SFK
 
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Makes sense. Thanks SFK
Though either way all 3 will likely still go to the ceiling rose, which may have a 3 hole loop in box, where the feed and loop feed will dive off into there respective conduits.
If so you would attach a wire onto the Red at the switch, pull it through enough and then pull the existing red back down to the switch.
 
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I'd say very unlikely the live loop in/out goes anyhere near the ceiling rose.
upload_2021-6-24_12-25-46.png

EDIT: Sorry rocky I totally misread your post, your quote deleted.
 
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I'd say very unlikely the live loop in/out goes anyhere near the ceiling rose.

Wouldn't that diagram require additional conduit boxes dotted around the ceilings though? One directly above the light switch for example?
 
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Wouldn't that diagram require additional conduit boxes dotted around the ceilings though? One directly above the light switch for example?
And there very well maybe...

Or inspection Tee's
 
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Thank you everyone for all your help and careful consideration.

All these variables are beginning to make me think this is probably a job that is beyond my comfort level.

Question to Jonny - can you show us an image of the cables at the ceiling rose?

I’ll have to wait until the end of the working day to isolate the consumer unit due to me & my partner working from home. But will do.

It's more likely that the lives are looped at the switches, not the rose. So I've assumed the two together are both live and the single is switched live.

I noticed when I moved into the flat that this switch’s on/off positions were reversed, so it would make sense that COM would be on the bottom with two live wires.

Good point about the earth. OP, unless you can check that the back box has been earthed by the conduit using a multimeter, then you'll have to fit a plastic switch. It seems your existing switch is metal, but that's no guarantee.

The previous owner seems to have been fairly reckless with his home improvements generally, and I have a feeling he probably installed metal switches without checking the earthing. Nevertheless, I suspect the CPC *is* acting as earth here, but obviously this is important to actually check.

I was planning on picking up a multimeter early next week. I was hoping to find a way to continue using metal switches as I prefer them for looks, but if they are impossible to make safe then I’ll swap for plastic.

Though either way all 3 will likely still go to the ceiling rose, which may have a 3 hole loop in box, where the feed and loop feed will dive off into there respective conduits.
If so you would attach a wire onto the Red at the switch, pull it through enough and then pull the existing red back down to the switch.

Not sure I’m able to follow here.

I'd say very unlikely the live loop in/out goes anyhere near the ceiling rose.

Wouldn't that diagram require additional conduit boxes dotted around the ceilings though? One directly above the light switch for example?

Thanks for the diagram Sunray. I’m afraid I don’t know how the flat was wired. Building was completed in 1965 and the building’s electrics don’t seem to have been touched much.
 
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The thing about conduit and particularly lighting circuits is they are frequenly easy to get another wire or two in.

the conduit is (or should be) run square to the walls so there will usually be 2 or 3 bends or fittings between the switch and light.

When you have the light down, take the switch off again and give the single red a little tug to see how easily it seems to move at the other end.
 
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