Issue with dimmer switch

[Simon Ross]

Hi all,

I wonder if anyone can provide a bit of advice. I've recently been doing some decorating in the house and part of that is to change the light switches in the house.

I'm in the process of changing 7 circuits in total, this consists of:

• Downstairs hall - 2 gang one of which is 1 way to control downstairs hall light and the other is 2 way to control the upstairs hall light as well.
• Kitchen - 1 gang 1 way
• Living room - 1 gang 1 way dimmer switch
• Upstairs hall - 1 gang 2 way (linked to downstairs hall light as above)
• 3 bedrooms - all 1 gang 1 way.

All of the light switches are decorative so are 2 way switches.

The issue I'm having is that I've changed all of the downstairs lights and wired them exactly how they were previously. Now whenever I turn the dimmer switch on in the front room, it's knocking off all of the bedroom and bathroom lights upstairs. When I turn the dimmer off the upstairs works fine as normal.

The dimmer switch has 3 red wires coming out of the wall and in to it, this is wired as previously with a wire going in to L1, COM and L2.

What am I doing wrong here?

Any help would be appreciated, tearing my hair out (what's left of it)

Thanks,

Simon

 

[Simon Ross]

SO The 2 "LIVE " wires go into C, and the other one in either l1 or l2.

Hi, no. The "non live" is in L1, the 2 "live" go in COM and L2

 

[pirate]

For a plastic switch, that dimmer looks very shiny and metallic...and is that an earth terminal?

 

[Simon Ross]

For a plastic switch, that dimmer looks very shiny and metallic...and is that an earth terminal?

It's the BG Nexus, it feels plastic but maybe it is metal?

There is an earth terminal in the socket yes.

 

[littlespark]

You'll be rubbing down that polyfilla and painting before you fit the new switch, right?.

L2 shouldn't have anything connected to it.
Its a dimmer switch. If you're using a neon screwdriver type tester, the light might not fully light up if the dimmer is set low - giving the wrong impression that there is no power.

The switch has an earth terminal. Use it

 

[pirate]

I think it's metal...and it's not the earth terminal in the box, it's the one on the switch...as littlespark said, use it...ideally use both of them!

 

[Simon Ross]

You'll be rubbing down that polyfilla and painting before you fit the new switch, right?.

L2 shouldn't have anything connected to it.
Its a dimmer switch. If you're using a neon screwdriver type tester, the light might not fully light up if the dimmer is set low - giving the wrong impression that there is no power.

The switch has an earth terminal. Use it

Ha, yes I'll be sanding down and painting the surface before refitting the light switch. The areas around the light switch were previously filled, poorly so I've redone them.

So if L2 shouldn't have anything in it, where should that wire terminate? In COM?

Thanks for the advice regarding using the earth.

I think it's metal...and it's not the earth terminal in the box, it's the one on the switch...as littlespark said, use it...ideally use both of them!

Thanks, if I'm earthing both the box and the switch is it a simple case of running a wire from the switch earth to where the earth is terminated in the box?

 

[pirate]

That would work...

 

[Simon Ross]

That would work...

Awesome, would 10mm single core be OK?

Something like: Nexans Conduit Wiring Cable 6491X 1-Core 10mm² x 10m Green/Yellow - https://www.screwfix.com/p/nexans-conduit-wiring-cable-6491x-1-core-10mm-x-10m-green-yellow/4048T?kpid=4048T&ds_kid=92700030947593839&ds_rl=1245250&ds_rl=1248181&ds_rl=1249481&gclid=EAIaIQobChMI8PrMwNO82gIVrBXTCh1r5gBwEAkYCyABEgLVBfD_BwE&gclsrc=aw.ds&dclid=CPjEpcjTvNoCFQkC0wodWEEKTQ

 

[123]

Good luck with that. 1.0mm or 1.5mm will suffice although I doubt any supplier will supply in in cuttings.

I'd love to see a photo of the attempt at doing it with 10mm though

 

[pirate]

That might be a bit of overkill, certainly rather larger than the wiring cables you are dealing with, and it might be tricky getting the switch back on the back box. Maybe some 1.5 or 2.5mm?

 

[pirate]

Beat me to it, 123!

 

[123]

Dimmer issue aside, I assume the rest of the light switches (that you thought where plastic but are metal) have been left without an earth connected either.

 

[pirate]

Simon Ross, as I have posted elsewhere today, you can get a 5m roll of 1.5mm at B&Q for £7...or if you prefer, 10m for £6 (No, I have no idea!) and if you are replacing a number of light switches with that Nexus type and they all have earth terminals on them, you will be wanting a bit of extra.

 

[Simon Ross]

Thanks for the advice re the cable, I'll have a look at some smaller stuff. Screwfix have 25m of 1.5mm for a fiver Nexans Conduit Wiring Cable 6491X 1-Core 1.5 mm² x 25m Green / Yellow - https://www.screwfix.com/p/nexans-conduit-wiring-cable-6491x-1-core-1-5-mm-x-25m-green-yellow/2682t

@123 and @pirate yes I'll be applying your advice of running the earth from the switch to the box (where it currently terminates) on all switches in the house.

I'm still a bit confused as to where the wire currently going in to L2 should be terminated?

 

[Ib≤In≤Iz]

One way you can find out what conductors go where is to dead test using a decent tester and a wander lead