Replace one switch with a dimmer in 2 way lighting circuit

[justin99]

Dear all,

I have checked the references, and cannot explicitally see the answer to my question so am posting.

The light in question is a landing light 5 x40W bulbs in total, with a switch upstairs and downstairs. Nothing unusual here!

Pending newborn, I want to replace the upstairs switch with a dimmer. Have bought a 400W 2 way dimmer and presume I replace the Com, L1 and L2 like for like. L1 and L2 currently have 2 wires in each.

Is it as simple as this? The circuit diagrams that came with the dimmer were a bit confusing. Also, I can't seem to screw the dimmer switch back onto the wall plate - even using the old screws? Is this a common problem with different switches - guess i should get some longer screws?

Also, there are several other wires (untaped) behind the switch. Should these be insulated, or is this normal practice?

 

[Spark123]

If it is 2 way I'd expect wires in all 3 terminals on the existing switch, com, L1, L2. My advice is not to use dimmers on staircases. There should be no bare wires in the back of a light switch, if they are earth wires they should be sleeved in green&yellow sleeving.

 

[C&GStudent]

Didn't your new switch come with some new screw?

Otherwise you'll have to get some new long ones.

 

[justin99]

Spark123 - any particular reason not to use dimmers on staircases?

The original screws were too short - will get some longer ones!

cheers
justin

 

[bernardgreen]

Spark123 - any particular reason not to use dimmers on staircases?

SAFETY

You may need to use the stairs in an emergency when visibility is already difficult due to smoke. If the dimmer is downstairs and set to lowest level you are literally in the dark when you need to see where you are going.

 

[justin99]

In this instance, the dimmer will be upstairs, so the safety side of things is ok, but thanks for your useful comment.

justin

 

[bernardgreen]

In this instance, the dimmer will be upstairs, so the safety side of things is ok, but thanks for your useful comment.

justin

You may need to go up-stairs to help / rescue someone un-able to reach the dimmer.

 

[pcboffinuk]

Justin,

To answer your original question, just replace the wires like for like in the new dimmer (making sure the circuit is isolated first!).

Should the dimmer be marked differently (e.g. L1 L2 & L3) then just be aware that these normally correspond to Com, L1 and L2 in turn which can lead to confusion.

If the non-insulated wires behind the switch are connected to the metal back box, then they are earth wires and should be sleeved with green/yellow insulation which is readily available. If the new dimmer switch is metal then there should also be an earth wire between the switch and the back box to ensure everything is earthed.

One way round the lighting concern others have expressed would be to consider a smoke detector at the top of the stairs with in built emergency light.....personally in the event of a fire I'm not sure I'd want to rely on the standard lighting wiring to be working anyway.

Hope that helps.

Gavin

 

[pcboffinuk]

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