How to Replace a Light Switch

Got a faulty or outdated switch? Changing it is easier than you thought. In this DIY blog, Speedy will show you step-by-step instructions on how to replace your light switch. It also includes all you need to know about safety, required tools, and common mistakes, so you can complete the job without breaking a sweat. 

Safety First 

It's worth noting that any changes in terms of the electrics in your house need to be compliant with the Building Regulations. In most cases, it's legal for you to replace a light switch yourself without professional help. However, if you need to create a new circuit or attach new wiring, it's compulsory to call a qualified electrician or notify your local authority according to Part P of the Building Regulations in the UK.

Before doing anything, you must turn off the main power supply and isolate the circuit to avoid electric shock. Find the fuse box in your house and flick off the fuse corresponding to the area you'll be working on. If you're unsure, it's best to turn off the main switch. This will cut the power to your whole house.

To be sure, test it again by using a voltage tester and confirm there is no electricity. Check out our PPE range to ensure you've got the necessary protection for this job and any other DIY task you want to take on. 

Tools and Materials Needed 

Here are the equipment and materials you need to replace a light switch. 

• Screwdrivers
• Voltage tester 
• Replacement light switch 
• Wire strippers 
• Work lights if you're working in dark corners of the house

Step-by-Step Guide to Replace a Light Switch 

After gathering all the necessary tools and ensuring the power is off, follow these four simple steps to replace your light switch. The guide is primarily for one-way switch replacement (where you control the light in one location). We also include the notes in case you have a two-way switch (where the light can be controlled by more switches).

Step 1: Remove the Old Switch

The exterior part of a switch you see outside is called a wall plate or faceplate. The first step is to remove the screws and expose the inside part of that switch. You can use a screwdriver to do this. When it’s opened, you'll see the electrical box connected to the current switch. You'll have to unscrew the existing switch by removing all the connections. Once this is done, pull the current switch out gently.

Step 2: Disconnect Wires 

Behind the current switch, you'll see all the connected wires with different colours. There can be a few different colour wires:

• Live: Brown or Red
• Neutral: Blue or Black
• Ground/ Earth: Green/ Yellow or Green
• Live conductors in multi-way switching: Black/Grey (sleeved brown)

Your job now is to disconnect them carefully.  

One important thing to remember before removing the wires is that you'll later need to connect them to the new switch in the same way. If you're not confident, note it down or simply take a photo for reference. Use your screwdriver to loosen the connection and detach them from the current switch.

It's also worth noting that wiring colours vary by installation and age. The colour variations shown are based on different wiring standards used over time. 

Due to this, it's important to identify each wire based on where it's connected and not just the colour. The position of each wire is outlines in step 3.

In most UK homes, a neutral wire may not be present in the switch back box, and instead will only be found in the ceiling rose of the corresponding light. If you do see a blue or black wire in a switch, it is most likely a switched live and should be marked with brown sleeving.

Step 3: Connect Wires to New Switch

Next, connect the wires to the new switch following the way it was done before. There are different terminals on the new switch. Each one is made for different coloured wires: 

• COM (Common): This is where the live wire (brown/red wiring) goes. It brings power into the switch. 
• L1: This terminal connects to the switched live wire going to the light. If your wire is blue/black, it should have a brown sleeve to show it can carry live current. 
• Earth terminal: Attach the green/yellow sleeved earth wire here. If the switch has a metal faceplate, double check that it’s also earthed for safety. 

If needed, strip the wire ends to create the ideal length for connection. When your wires are prepared and in place, tighten the screws again to secure the connection. Make sure the wires are held tightly in place by gently pulling on them. If they move, they’re not secure.

For two-way switches, it’s a bit more complicated. You might see more wires inside the switch, as there will be an extra 3-core and earth cable (brown, black, grey, and earth) to link the two switches. If you want to replace the light switch, don't forget to take a photo and follow the same connections it previously had.

Read the instructions below if you're adding another switch to your one-way switch system.

At the first switch:

• COM: Live feed (brown/red wiring) from the power supply. 

• L1 and L2: Black and grey cores of the linking cable. You can put a brown sleeve to show they can be live. 

• Earth: Attach the green/yellow sleeved earth wire to the mounting box and faceplate. 

At the second switch:

• COM: Connects to the wire that goes directly to the lighting unit.  

• L1 and L2: Connect to the same traveller wires (Black and grey cores of the linking cable). You can put a brown sleeve as well. 

• Earth: Attach the green/yellow sleeved earth wire to the mounting box and faceplate. 

Step 4: Reassemble 

Now that all the wires are connected, you just need to carefully push the new switch into the box and screw it back in to keep it in place. Again, attach the wall plate, and your light switch will look brand-new. Make sure that all of the wires sit inside the back box and don't get pinched as you're reattaching the faceplate.

The final step is to turn the power supply on and test the switch functionality. If the new light switch doesn’t work or sparks after installation, check the common mistakes below and ask for professional help if needed.

Common Mistakes to Avoid 

Some common mistakes can lead to serious hazards if not carefully handled. Avoid these while replacing your light switch. 

• Similar to fitting a security light, you need to turn off the power supply. Not doing so can lead to serious health risks. If you're not confident, it’s best to ask for help from a professional.
• Mixing up wire connections can be the reason why your new switch isn't working. Make sure to screw them in the right place and follow the same setup used in the old switch.
• Over-tightening screws can damage the wires. Frayed or burnt wires can lead to short circuits or fire risks.
• Don't ignore the ground wire (earth wire) as it's whole purpose is to act as an additional safety measure. Ensure you connect it to the right place to comply with safety regulations.
• If your light stays permanently on, the switched live and permanent live wires are in the wrong places and need switching.

Sometimes the problem doesn’t lie in a faulty switch, and your light switch may not work due to more complicated reasons. Call a certified electrician in case the wires look damaged, or if you're not sure about wiring types.

Start Replacing Your Switch Today!

With these simple steps, you can change your light switch at home without a complicated process. However, always keep your safety in mind and call a professional if you're new to DIY projects.

Get started today and make your home an ideal place to enjoy! From simply replacing a light switch to more complicated house-building projects, Speedy has the right tools for hire. 

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