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

 

[ipf]

You're guessing with your wiring. Guessing, you could say, is like sticking a pin in......don't do that!

 

[Simon Ross]

You're guessing with your wiring. Guessing, you could say, is like sticking a pin in......don't do that!

Hi, I've wired it in the same way as it was before, 2 of the wires are live and one isn't.

 

[123]

If the dimmer in the front room is a 1 way only, then you have split the loop feed there. You should have 2 wires in COM and 1 in L1, nothing in L2

 

[Simon Ross]

Hi @123 thanks for the reply.

From my basic knowledge of light switches I thought this was the issue so I put the wire which was in L2 in to the COM as well and it didn't work. It tripped.

I can try again?

 

[ipf]

Hi, I've wired it in the same way as it was before, 2 of the wires are live and one isn't.

You haven't. How are you testing which are live?

 

[littlespark]

That was my thought too. Should have been a looped live in Com and the switchwire to the room light in L1.
Its starting to get confusing. If you only have red wires at the switch, theres no reason for it to trip out. It would either not work at all, or be on all the time, if it was connected incorrectly.
Theres only 3 wires, right? You can only connect them up a handful of ways

Any further connecting/disconnecting is going to confuse you as well. Suggest you call International Rescue, or a local sparky with the correct equipment for tracing cables. There might be a forum member in your neck of the woods with a sunday afternoon spare.

 

[Ib≤In≤Iz]

Is this 2 or 3 plate ?

 

[Simon Ross]

You haven't. How are you testing which are live?

Probably not. I'm using a mains tester screwdriver.

That was my thought too. Should have been a looped live in Com and the switchwire to the room light in L1.
Its starting to get confusing. If you only have red wires at the switch, theres no reason for it to trip out. It would either not work at all, or be on all the time, if it was connected incorrectly.
Theres only 3 wires, right? You can only connect them up a handful of ways

Any further connecting/disconnecting is going to confuse you as well. Suggest you call International Rescue, or a local sparky with the correct equipment for tracing cables. There might be a forum member in your neck of the woods with a sunday afternoon spare.

Technically there are 4 wires, 1 is the earth which is terminated at the knockout box, there are 3 red wires which require terminating at the switch, 2 live one not live.

So should both lives go in to COM and the switch should go to L1?

Is this 2 or 3 plate ?

Sorry, don't know what 2/3 plate means.

 

[123]

The trouble is your test equipment is totally inadequate. I can see no reason why putting the cable that was in L2 into COM would cause anything to trip as this will be exactly the same as when the dimmer is OFF.
Is there only 1 lighting circuit in the property?
Can you post a photo of the cables at the back of the switch?

 

[123]

Also if you have fitted metal switches the CPC (earth) should be connected to the earth terminal on them

 

[Simon Ross]

The trouble is your test equipment is totally inadequate. I can see no reason why putting the cable that was in L2 into COM would cause anything to trip as this will be exactly the same as when the dimmer is OFF.
Is there only 1 lighting circuit in the property?
Can you post a photo of the cables at the back of the switch?

I thought as much, but don't have anything else at my disposal other than an old multimeter.

There is only 1 lighting circuit yes.

I can take a picture, just out at the minute so I'll take one when I get back in.

Also if you have fitted metal switches the CPC (earth) should be connected to the earth terminal on them

They are plastic light switches, the nexus range from BG.

 

[littlespark]

OK. 3 reds, 1 green/yellow.
Single cables wired in conduit it seems.
2 of the reds are permanent supply live. One coming from the board, or a previous switch position and one going out to the next switch as its supply.
The 3rd red is the switchwire running up to the light. (would have been handy if this had a bit of tape put on it when it was disconnected for identification)
Originally it sounds like you connected what should be a permanent live to the wrong side of the switch, so that all the other switches in the house lost their supply until you turned the living room switch on. (or off, if it was connected to L2)

Is your dimmer replacing another dimmer or a regular switch? As a layman, you may not realise that some lamps are incompatible with dimmer switches. (CFL and most LED are not compatible. Old filament and halogen lamps at OK, and LED ok if the box says they can be dimmed)

 

[Simon Ross]

OK. 3 reds, 1 green/yellow.
Single cables wired in conduit it seems.
2 of the reds are permanent supply live. One coming from the board, or a previous switch position and one going out to the next switch as its supply.
The 3rd red is the switchwire running up to the light. (would have been handy if this had a bit of tape put on it when it was disconnected for identification)
Originally it sounds like you connected what should be a permanent live to the wrong side of the switch, so that all the other switches in the house lost their supply until you turned the living room switch on. (or off, if it was connected to L2)

Is your dimmer replacing another dimmer or a regular switch? As a layman, you may not realise that some lamps are incompatible with dimmer switches. (CFL and most LED are not compatible. Old filament and halogen lamps at OK, and LED ok if the box says they can be dimmed)

Hi @littlespark thanks for this, help is much appreciated. Everything you've said is correct, I've attached a picture for reference, the black lines I drew on to help me wire it correctly (seems daft now haha).

The light is a pendant with an LED bulb, the dimmer switch states it works with LED and it does work without an issue, it's only the upstairs lights where there is an issue.

In the picture, using my mains tester only, the wire in the left terminal is not live, the 2 to the right are live.

The sequence of terminals is L1/COM/L2

 

[telectrix]

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

 

[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!