Wiring a Light Switch in the Middle of a Circuit

hands working on wires behind light switch
  • 2-5 hours
  • Advanced
  • 100-300

There are many different things around the house that you can learn to DIY with some pretty straightforward trial and error, making mistakes, and trying again. Wiring a light switch in the middle of a circuit is not one of them.

When it comes to wiring a light switch in the middle of a circuit or doing anything else with the electricity in your home, you definitely need to know what you're doing and make sure you're doing it safely.

DIY is a great way to get hands-on and personalize your spaces and save money but it also comes with a risk when you aren't well-prepared and knowledgeable in what you're doing, especially when it comes to your electrical system.

So What Is a Circuit?

If you're going to be doing anything with the electricity in your home, you need to have at least a passing knowledge of how electricity works and the basic components of your electrical system. For example, you need to understand what a circuit is.

Electricity has a current, or a flow, much like the way that water flows in a stream. If you put a dam in the middle of the stream, the water flow stops.

Electricity is the same way in that it needs somewhere to go, something to give power to. Without connecting to something, electricity just sits there unmoving.

When electricity has something to connect to and there is a power flow, this is a circuit. This is the electricity flowing through wires or objects or anything that's connected to the electrical system.

When you connect a wire from the positive side of the power supply to the negative side of the power supply, you create a short circuit. This is when the power flow is too strong because it's trying to power too many things at once, so to speak.

Circuit breakers prevent the power from working too hard, which can create a fire hazard and other safety issues.

That's why adding a light switch into the mix can be difficult. You need to know how to do this the right way and the safe way, so you don't cause any problems anywhere along your power supply.

Light Switches for the Experts

So, everyone knows how light switches work. You flip the switch down and the light goes out while if you flip it up, the light comes on.

Duh. But how does a light switch really really work? What's going on back there in the wall among the wires that actually make this happen?

The light switch itself is more than the little thing you move up and down and the faceplate behind it. On the other side of this faceplate is the actual switch that makes a light switch work.

The "hot" wire, which is the wire with the power flowing through it, goes to the switch. Another power wire connects to the fixture, which is the outlet or lights the switch is powering.

When the switch is turned off, the power flow is stopped. It’s like putting a dam in the stream.

When the switch is flipped back on again, the power flow is flowing again. The switch itself is like a stop-and-go traffic light that you manually control.

If you want to add a light switch to the middle of a circuit, you need to know this stuff and you need to know how to add the switch safely. It's not an easy DIY but it is something you can learn how to do.

Don’t slip any safety steps and if you find yourself confused or overwhelmed, don’t attempt to guess. Consult with an electrician, rather than attempting to come up with a fix on your own.

Most of the time, adding a light switch is a fairly straightforward procedure and it is possible for the everyday DIYer to learn. But sometimes, you might have old wiring or something different happening with your wiring and this can make things more complicated.

How It Works

A standard single-pole switch, which is the switch that has the thing you flip up and down, has two brass terminal screws that are used to connect it to a circuit. You connect the switch to the black wire, the "hot" wire, which is coming directly from the circuit breaker panel, to add the switch to the power grid.

This black wire from the circuit breaker goes to the switch, while the black wire used to power the light or the outlet that you want to control with the switch runs between the switch and the fixture.

In most electrical configurations, there are three main wires powering circuits throughout the house. The black is the wire that carries the electricity, the green wires are grounding wires, and white wires carry electrical current through the home without connecting to circuits and switches to act as a main power flow source that black wires can connect to.

How to Wire a Light Switch in the Middle of a Circuit

Adding a switch to the middle of a circuit means that the switch will control anything and everything connected to that circuit, whether it is all the electrical outlets in the room or a single light fixture overhead.

Power Off

Turn off the power to the entire house.

Technically, all you have to do is turn off the power to the circuit you will be working on. However, sometimes wires get crossed and you can never take too many safety precautions when it comes to working with electricity so please play it safe and power off the entire system by flipping all of the circuits at the power box and turning them off and turning off the main breaker, too.

Use an electrical tester to ensure that the power is indeed off and that it is safe to work. An electrical tester is a basic piece of equipment that you should have if you plan on doing any electrical DIY stuff.


Strip the wire. You will want to do this with a razor knife and carefully cut away the sheathing, the outer casing, that covers the wires.

Work carefully to make a clean cut. You want to cut the sheathing but not the insulated wire coatings, the black and white coatings on the wires.

Remove enough of the sheathing to get wires to work with. Use wire strippers to expose the wires so you can connect them to the switch.


Unless there are already loose wires here that have been capped off for the addition of a switch, you will need to cut the wires at this point. The cut ends of the wires will connect directly to the switch.

Since you are cutting wires, you now see the importance of turning off the power and testing it. Use wire cutters and cut all three wires, the green, the white, and the black.

You need to re-connect both ends of every cut wire, so don’t let these wires fall behind the wall or get lost. All ends of all wires must be re-connected to the switch and you should not have any loose wires or bare wire ends when this DIY is over.


The ends of the wires are inserted right into the switch, which has different terminals for the wires to connect.

A flathead screwdriver should work to loosen the screw terminals. There are silver, green, and brass terminals.

Connect the wire white to the silver screw, which is tightened back down with a clockwise motion. The green wire connects to the green terminal.

Connect the black wire to the switch using the brass screws. The end of the wire must be placed inside the terminal under the screw and the screw is then closed down on the wire to secure it.

Make sure all wires are connected and everything is secure before you attach the light switch terminal to the faceplate and mount it to the wall. Now is a good time to swap out your faceplate for a pretty decorative one if this is what you want.

Wiring a Light Switch in the Middle of a Circuit

Messing around with your electricity can be dangerous, but it can also become a DIY task. If you practice safety and work with care and precision, you can complete this task safely and end up with a new switch that actually works.

The more DIY tasks you take on, the more you will learn about how your home works and the more you will be able to take on little tasks and projects that can improve your spaces. DIY can be scary, but there's a whole lot that you can do when you put in a little research and some work.

Light Switch FAQs

How do you install a dimmer switch?

Dimmer switches can dim or brighten lights, rather than simply turning them on or off.

Dimmer switches are designed to work with different types of lights. For example, there are dimmers made to work with LED bulbs and those made to work with incandescent or halogen bulbs.

Some dimmer switches are made with the same configuration as single-pole light switches, which means you can use the same method to install dimmer switches once you know how to install a single-pole light switch. Choose a dimmer switch that is made for the type of light bulb you want to dim, use the same method for wiring a single pole switch, and everything should work just fine.

Are there other types of light switches?

Though the single pole light switch is by far the most common and the one that most people have, there are actually more than 20 different types of light switches you can use.

This includes touch switches, four-way switches that have four poles rather than one, motion-activated switches, and even sound-activated switches.

How do you wire a smart light switch?

Smart light switches connect to your smartphone or to a whole home smart system, and they can be turned on and off digitally using a wireless signal.

Smart light switches are designed to be wired in the same way as single-pole light switches so once you know how to wire a single-pole light switch, you can simply swap this out for a smart switch instead.

All the technology is already integrated into the switch, not into the wiring, so the wiring doesn't change for smart systems. It's all about the switch itself, which from an electrical standpoint works the same way as a classic single-pole design.

Do you need a permit to add an electrical switch?

For lots of projects, you need to hire a professional for one really good reason: permits are required. You can't install your own water heater in most states, for example, and you can't fool around a lot with your own electrical wiring without getting a permit, either.

Often, professionals know exactly how to get these permits and, sometimes, may be required to get them. So, do you need a permit to add a switch to an electrical circuit?

That all depends. Every single state has its own codes and requirements, and every state has different rules about what types of tasks need permits.

Most of the time, however, adding a switch is not something that requires a permit. Adding a new outlet or a new fixture, however, might require a permit.

If you're not sure, call your local housing authority and ask them where you can get information about electrical permits. If they don't know the answer, they can tell you which government office to call to find out.

Further Reading

4 Common Light Switch Problems

5 Tips for Installing an Outdoor Light Switch

Changing Ceiling Fan Light Switch

How to Install an Automatic Light Switch

How to Install a Double Switch Light

How to Install an In-Line Cord Light Switch

How to Install a Remote Light Switch

How to Move a Light Switch

Motion Sensor Light Switch Wiring Explained

Troubleshooting Tips for Light Switch Wiring