What does the neutral wire do? Neutral wires are easier than you think!

“What does the neutral wire do?” is a common question among homeowners, DIY enthusiasts, and anyone interested in understanding the basics of household electrical systems.

Getting a light switch neutral wire to your switch brings connotations of ripping walls apart and turning your home into a building site, but that does not have to be the case as we discuss below. 

Electrics are Dangerous!

Warning, electrics are dangerous and you should seek the help of a qualified electrician. Even if you think you know what you are doing, you could be wrong. Risk of fire, risk of death. Make sure you turn off any electrics at the consumer unit before working on them and test with an appropriate tool that the circuit is not live.

Shortcut (TL;DR): Fig.1 is what most UK homes have and Fig.4 is the tweak to get a neutral to the switch and permanently energise the bulbs.

Wire Colours

In some older buildings, you may have red and black cabled in the UK. In this case, red is normally live and black is normally neutral.

First, what is a neutral wire and why might I not have one?

For a traditional switch to turn a light on and off, it needs to make and break the circuit. Traditionally in the UK, this is wired such that the live (brown) and neutral (blue) wires (old houses may have red and black cables respectively) from the main power source (the incoming power) go to the light fitting first, then the live is sent to the switch and finally the switched live (the live that is made and broken) is sent back to the light. We refer to this as “light-first wiring” which means you do not have a neutral at the switch. The live from the light to the switch uses the brown wire, then the switched live uses the blue wire and is normally marked with some brown tape to indicate it is actually a switched live and not a neutral.

diagram showing light first wiring
Fig. 1

It’s important to note that your home may be wired differently to this, especially in newer houses and in mainland Europe where the incoming power goes to the switch first and then to the light. We refer to this as “switch-first wiring” which means you do have a neutral at the switch.

diagram showing switch first wiring
Fig. 2

What if my switch controls multiple circuits?

It is more than likely that a switch has more than one lighting circuit wired to it. In this case, it’s best to try and consider only one of the circuits (and its corresponding wiring) in isolation. When you have completed the latter steps and got neutral to the switch, then you can permanently energise the additional circuit(s) at the switch location by joining the live and switched live for each circuit together.

multiple circuits 1
Fig. 3

What if I have two-way switching?

If the light in question can be switched from two locations then first work out which switch wires directly to the light (the first switch) and which switch just wires to the other switch (the second switch). See Fig. 1. You should focus on the first switch which wires to the light, safely disconnecting the second one. Once you have got a live and neutral to the first switch by following the latter steps, you can send the same live and neutral to the second switch.

How can I tell if I have light-first or switch-first wiring and whether I have a neutral?

Most of the time, you can tell whether you have a neutral at the switch or not by removing the switch and having a look at the wires inside. Firstly, if you see a blue cable with brown tape, then that’s a switched live and you likely don’t have a neutral. If you don’t see a blue cable with brown tape but you only have one blue and one brown cable (for that circuit), then you still likely don’t have a neutral and the switched live has just not been marked with brown tape. If you have switch-first wiring, then you will have the cable coming from the consumer unit and the cable going to the switch. See Fig. 1 & Fig. 2 to determine which scenario you have.

Why do I need a neutral wire?

Smart Home requires a neutral to power it. If you were to directly swap a traditional switch that uses light-first wiring, and therefore has no neutral at the switch, then the power for the lights would be running through the switch which it is not capable of supporting.

How do Smart Bulbs help?

A smart bulb has all the electronics inside it to allow it to effectively switch itself on and off (as well as dim and perhaps change colour if it supports it). This is what makes them smart and allows you to use your phone or other gadgets such as Smart Switch to control them, (read here about how our Smart switch works). Since all the switching and control is built in to the bulb, a traditional switch is not necessary and, in fact, turning off a smart bulb at a traditional switch means that it is physically not powered and so can’t be turned back on from anywhere else.

This means that actually, we want to permanently power (or “permanently energise”) the bulbs so that we always have control of them from our smart devices.

So how can I get a neutral to the switch and permanently energise my smart bulbs?

If the room in question has switch-first wiring then you already have a neutral. This means you can join the light switch neutral wires together and join the live wires together and you will have permanently energised your bulbs. Then connect these same live and neutral wires to the Smart Switch (you might need a separate connector block if the wires don’t fit into the terminals) and your wiring is complete.

If the room in question has light-first wiring then you do not have a neutral. To tweak this, you need to track down the the first light fitting that the incoming power goes to, and remove the ceiling rose or the bulb, depending which kind of light fixture you have. In here, first remove the wires that go to the switch. Then, by connecting all the live wires together and all of the neutral wires together, you will have permanently energised your smart bulbs. Now, all you need to do is join these live wires to the switch cable’s live and the neutral wires to the switch cable’s neutral and you have sent the live and neutral back to the switch which you can connect them to the corresponding terminals on Smart Switch . See Fig. 4

permanantly energising 1
Fig. 4

In Conclusion

In conclusion, the neutral wire is a crucial component of household electrical systems, providing a return path for electrical current and enhancing safety. Understanding the role of the neutral wire can help homeowners troubleshoot electrical issues, and make informed decisions when installing new electrical devices or upgrading their existing systems. With the rise of smart home technology, the importance of the neutral wire has only increased, as many smart devices require a stable connection to function properly. By investing in a smart light switch, homeowners can not only enhance the functionality and convenience of their lighting systems, but also improve their productivity and energy efficiency. So, next time you’re wondering “What does the neutral wire do?”, remember that it’s not just a matter of safety – it’s also a key factor in creating a smarter, more productive home.

Rithum Switch

Rithum Switch directly replaces an existing light switch and provides a convenient location in each room to control your smart home.




  1. A neat solution BUT 1) If you sell the house and someone swaps at the smart switch for a ‘normal’ switch and turns it on – BANG ! 2) Two way switching will short the L and N together so it’ll be BANG again !!!

    1. Thanks for the comments. With regards to point (1), a competent person (read: electrician) should notice that the switched-live marker has been removed and it is therefore not one, but a neutral. We would also expect the seller to take their smart switches with them and turn the switches back to standard ones, after all, they paid for them. With regards to point (2), the secondary switch should have been removed from the circuit or a second SmartSwitch installed there if the instructions were followed.

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