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Two Gang Light Switch Wiring Confusion for Swapping With Smart Switch

Postby mattih52002 » Sun Apr 17, 2016 2:02 pm


I'm looking for a bit of advice. I'm wanting to replace a two gang light switch (the second switch doesn't appear to operate anything) with a smart switch so that I can control its operation through Wifi or z-wave or whatever technology I choose.

One of the switches (left) currently operates 15 CFL bulbs built outside on our driveway.

The colour coding is what is confusing me. All the smart switches I've come across require a neutral line. Neutral to me is blue but googling around it could also be grey.

Attached are some screenshots of the switch and its wiring. Can someone explain the colour coding to me and what each mean? I assume one is live, switched live, Earth (yellow/green) etc.
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Postby ericmark » Tue Apr 19, 2016 8:23 am

In the UK we traditionally use the ceiling rose, both to support the cable to lamp and to work as a junction box. So in the main we do not take the neutral to the switch.

There was a move to use the switch as a junction box when installing low voltage lamps with a re-wire as the electronic transformers do not have the space in the cable box to take more than one cable. But this only happens with a rewire there are junction boxes made to replace the ceiling rose which in the more common method.

There are good reasons for the design.
1) Better loop impedance.
2) Line at lamp for fans or emergency lamps.

There are lamps which can be controlled by a remote which replace the ceiling rose. But at the switch it is a problem having no neutral, there is a move to create a standard through current on a lamp, in industry we have the 4 ~ 20 mA system so the first 4 mA can be used to work the switch, however in domestic no agreement has been reached.

There is a trade off, that current required to run the switch has to run at all times, so a leak current of 1 mA = 0.23 W so over 24 hours = 5.52 Wh so the same as leaving a 6W LED running for an hour a day. So manufacturers are not agreed as to the amount of current that is acceptable.

If you stick to one manufacturer like "Megaman" you could likely get dimmers and PIR's to work with LED lamps. But swap the bulb and you can get the flash as the current builds up in another manufacturers bulb.

My son looked at special bulbs which allow WiFi control however the same problem, to work the light has to be left on, without the WiFi device you can't turn on lights, and the bulb when not in use needed more power than when in use assuming 4 hours on and 20 hours off per day.

When a light bulb was typically 60W a device to switch them off automatically made some sense, however today when typical bulb is 6W hard to find an automatic device which does not use more than the bulb.

You can get replacement PIR for you wall switch which claims to work with all lights but I have worked where lights are PIR controlled and real pain when light go off when using PC as you have not moved enough.
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