One-way switch to Dimmer Switch

GarethP · 28 Apr 2004

I am trying to replace a standard plastic single switch with a plastic single dimmer switch (remote controlled).
The current switch has one connection labelled 'Common' (at the top end) and two others labelled 'one way' and 'two way' (both at the bottom end).
There are two red wires and one green/yellow wire extending from the wall.
One red wire goes to 'Common' and the other goes to the connection labelled 'one way' (the connection labelled 'two way' is not used- I assume that the switch is in fact a two way switch but is in effect one way, therefore).The green/yellow wire is unwired and tucked away in the mounting.
The new switch has two possible connections - one marked 'Live' with an arrow, and the other a zig-zag with an arrow through it.

I believe that the red wire is usually the live wire, but unfortunately there are two red wires here. Is the red wire in the 'Common' connection the live wire, and should it go the 'Live' connection on the new switch (obviously)? And does the other red wire then go to the zigzag/arrow symbol connection?
Please help...

PS I bought the dimmer at BandQ, but I think this one here is it if you want to see what it looks like: this

Inspector · 28 Apr 2004

On the link you provided there's an Installation and Wiring Details link

Sounds like your right

GarethP · 28 Apr 2004

Thanks for replying.

I know that there is a link. It gives the same instructions as those provided with the dimmer. The trouble I have is with recognising which wire is which on the present switch. I need to know which is the live wire, but since (I believe) a two-way switch has been used in the place of a one-way switch it has confused me a little, as the markings are not as they would be on a one-way switch. Furthermore, both the wires are red, which does not help.

I guess what I'm asking is, 'If a two-way switch was used as a one way switch, then would the live wire go into the connection marked 'Common'? (see original description of the switch).

Thanks again.

plugwash · 28 Apr 2004

you should be able to fit the reds either way round

ban-all-sheds · 28 Apr 2004

Gareth - what makes you think that it is reasonable to work on electrics without even the most basic tools, i.e. something that will identify live conductors, or measure voltage etc?

Also, if the box is metal, then the earth conductor should be connected to it.

And BTW - a 1-way switch would have had the same markings, and your problem in identifying which wire is which would have been identical.

Inspector · 28 Apr 2004

The one which was in the COM terminal is most likely the permanent live supply from the lighting circuit. A meter is need to to verify this (ie it will be live and the other one won't be when they're both disconnected).

So the (zigzag & arrow) terminal will have the other red (load) in it.

If the dimmer or switch back box is metal clad then they need earthed.

GarethP · 29 Apr 2004

Thank you all for your replies. As ban-all-sheds handily points out it is best not to tinker with electrics unless it is safe (though once the electricity is turned off it's not really electrics and they're just metal wires).

At any rate, since the summer is round the corner and I fancy a tan, so I waited to ring an electrician friend, and I can now dim the lights.

Plugwash said what the electrician said, which is that they are both live wires. Inspector, I am sure everything you said was correct also, so thank you.

As for the earth wire, the box is plastic (I think I said that originally?), so no danger there.

Thanks again.

Gareth

ban-all-sheds · 29 Apr 2004

GarethP said:
Thank you all for your replies. As ban-all-sheds handily points out it is best not to tinker with electrics unless it is safe (though once the electricity is turned off it's not really electrics and they're just metal wires).

Actually what I said was it is best not to tinker with electrics if you don't possess the correct tools.

Plugwash said what the electrician said, which is that they are both live wires.

That's not what plugwash said - he said you can connect them either way round, not the same thing at all. They can't possibly both be live. Hopefully you misunderstood or misheard your electrician when he said they were live and switched live.

As for the earth wire, the box is plastic (I think I said that originally?), so no danger there.

You said the switch was plastic - you could still have had a metal box. Don't be tempted to cut the earth wire back, it'll be needed if anybody ever fits a metal switch.

kendor · 29 Apr 2004

plugwash said:
you should be able to fit the reds either way round

Not if you want it to work!
You must verify which is the live and which is the switchline
Isolate the lighting circuit and use a meter on continuity setting to see which wire goes to the lampholder or light fitting, this is the wire you put in the terminal with the wavy line(zig zag) and arrow on it.
Just presuming that the wire in the common terminal is the live is wrong an ordinary switch will work either way, it could have been screwed back to the wall upside down.

plugwash · 29 Apr 2004

kendor said:
an ordinary switch will work either way, it could have been screwed back to the wall upside down.

so should a dimmer unless it is doing something really dodgy like running power live-earth

kendor · 1 May 2004

plugwash said:
kendor said:

an ordinary switch will work either way, it could have been screwed back to the wall upside down.

Click to expand...

so should a dimmer unless it is doing something really dodgy like running power live-earth

ABSOLUTELY NOT!!!!
the output from a dimmer is via a triac and you CANNOT wire it back to front like you could a normal switch.
The wire to the light must only be connected in the"Sine wave with an arrow through it" terminal.

breezer · 1 May 2004

i was always under the impression that as its ac going through the triac it wouldn't matter which way round it goes.

usless but true?

triac is an anagram of the bloke who invented its daughter "trica"

believe it or not

ban-all-sheds · 2 May 2004

This has come up before see here

kendor · 2 May 2004

The argument is that if you are going to connect the switch up then live goes to L or C and the load goes to the wavy line with an arrow through it, this is the CORRECT way to connect it.
the output IS a triac but internally inside the switch, the electronics that trigger(or to use the correct terminology gate) this triac are fed by the live wire and need to see a permanent live at the common or live terminal as it's reference for the timing of firing the gate of the triac at the correct period of the sine wave (phase angle triggering).

plugwash · 2 May 2004

kendor it can't make any difference as there is no neutral at the switch anyway

so any current the dimmer draws has to go through the bulb

whichever way round you conenct the dimmer there will be a tiny current in the buld before the main triac in the dimmer triggers

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One-way switch to Dimmer Switch

breezer

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