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19/02/2018

Hot to get a neutral wire to a UK light switch [Theoretical]

For the majority of UK homes (The older ones at least) our lighting switches are wired up with a system called 'loop in ceiling' where all the light fittings in the ceiling (ceiling roses) are wired in a loop, with a switched live being taken from the rose to the switch. This can potentially save cable and simplify installation, but causes issues when you want to install Home Automation type switches such as the Sonoff T1 that need a Neutral to be able to power themselves.

This is something I've been mulling over for a while, and someone has asked for more details. So here it is, a quick and dirty blog post.

Below shows a standard wiring layout for a single switch and bulb, as you can see there's no neutral in the switch, only live in and switched live out.


The Problem (Click to expand)

So, can we get a neutral to the switch without tearing the walls apart? Kind of!

I am not an electrician. This may not meet building or safety regulations. This is untested! Do so at your own risk! Electrical work should be carried out by a qualified electrician! ETC

So what if we re-wire the feed to the switch so there's a live and neutral feed? Well, it's do able but you'll the switched live to the bulb, so you wont be able to turn it off and on. What we need is another wireless device switching the power. Enter the Sonoff Basic, a Home Automation WiFi Smart Switch.

So if we shuffle some wiring around in the ceiling rose and find somewhere to conceal the Sonoff Smart Switch in the ceiling or light fitting, we're in business. Note: Don't wire a standard switch across Live and Neutral, as you may find it has explosive results. 

Modified Wiring Layout (Click to expand)

There's one small caveat, I don't know if the Sonoff T1 and native app will allow you to switch an external device such as the Sonoff Basic. To achieve this, you may need to flash the Sonoff devices with an alternative firmware such as arendst's Tasmota Firmware and handle the logic with HTTP or MQTT.

Another alternative method would be to skip the Sonoff Basic and permanently wire in a smart bulb such as a Phillips Hue or Mi-Light, and use some magic to convert the MQTT / HTTP from the Sonoff T1 to whichever flavour of RF your smart bulb uses.

I hope that helps!

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