Wiring a single-pole switch (aka a standard light switch) is one of the home improvement tasks you'll encounter most often in DIY electrical repair. That's because virtually all light switches that control 120-volt fixtures are single-pole switches. Most light switches are also single-throw, which means that they are simple on/off switches (as opposed to a three-way switch).
In any electrical circuit, the function of a switch is to interrupt the hot leg (power supply) of the circuit. When you have multiple wires in a switch box, however, it isn't always clear which two hot wires you need to connect to the switch. It usually isn't difficult to identify wires when the circuit comes to the switch before going to a light fixture, but things get a little more complicated when power goes to the lights first and then comes to the switch or when the circuit branches off in the switch box to feed another device, such as a receptacle. Working with three-way switches is even more complicated, and sometimes, the best way to resolve uncertainty is to call an electrician.
As long as you're clear on what a single-pole switch is supposed to do, though, you shouldn't have any problem connecting it. Sometimes, when you're replacing an existing switch, the easiest way to handle the wires is to note which terminals on the old switch they are connected to and to make sure you connect them to the same terminals on the new one.
What Is a Single-Pole Switch?
A single-pole switch is one that controls a single circuit — it turns a light on and off from a single location. It connects to a single hot wire (the feed wire) bringing power to the switch and connects to another hot wire that sends power to the light only when the switch is on. When the switch is off, only the feed wire remains hot; the other wire has no power because the switch breaks the circuit.
A standard light switch is the most common example of a single-pole switch. It has two brass terminals and a ground screw, and because its purpose is only to interrupt the hot leg of the circuit, it has no terminals for a neutral wire. Some single-pole light switches do have neutral terminals, but that's because they have some functionality, such as smart features or an illuminated toggle, that needs electricity at all times.
A three-way switch, which is always used with another three-way switch to control one or more light fixtures from two different locations, has two brass terminals, a ground, and an extra terminal (usually black) known as the common terminal. It's also a single-pole switch, but it's double throw because the lights can come on when the toggle is up or down depending on the state of the other switch.
Understanding Switch Wiring Configurations
While hooking up a single-pole light switch is easy, determining which wires to use may not be depending on the circuit configuration. Some common ones you might encounter include:
- Middle-of-circuit: The live cable, which is connected to the electrical panel or to another device in the circuit, comes into the switch electrical box; a second cable goes out from the box to the light fixture. In this configuration, you'll find only two cables in the box, and you can hook up the switch without even knowing which cable is which (although it's best to test first). The neutral wires are twisted together and capped, and the ground wires are also bonded and connected to the ground screw on the switch.
- End-of-circuit: Sometimes, it's more expedient to feed power to the light first and connect the switch to the light. In this case, only one cable enters the box. With the traditional configuration, both the white and black wires in the cable are used as hot wires, so the white one must be wrapped with black electrical tape to indicate that it is a hot wire and not a neutral wire. In newer installations, the cable has an additional hot wire (usually red), and only the black and red wires connect to the switch. The white is neutral and is capped inside the box; it remains available for use with a smart switch or other device that requires a neutral.
- Switch feeds another device: An additional cable in the switch box may be feeding another device in the circuit, such as a receptacle. Commonly, the black wires from the live cable and the cable going to the other device are spliced together, and a short length of black wire extends from the splice to attach to the switch (this is called a pigtail). The black wire for the light fixture connects to the other switch terminal.
- Three-way switch: Three-way switches are always wired in pairs, and depending on the configuration, you might find one or two cables in the switch box depending on the placement of the switch in the circuit. One of the cables has a red wire that is used to connect the switch to its companion. To understand three-way switch electrical wiring, it's helpful to study a diagram, such as the one at Electrical 101.
Things You'll Need
How to Wire a Single-Pole Switch
As with any wiring project, it's important to turn off the circuit breaker controlling the circuit before you touch anything. In general, the breaker should be off for the entire time that you're working.
1. Test the Wires
It isn't necessary to distinguish the line, or feed, cable (which is the one supplying power) from the other one for simple switch wiring because the switch will work whether the line cable is on the top terminal or the bottom. It's important to test them, though, to make sure they're off. Touch one of the leads of a multimeter to the ground terminal and the other lead to each of the switch terminals in turn. The meter should read zero. You can also use a noncontact voltage tester. Hover it over both terminals and make sure the light stays off.
2. Disconnect the Switch
Loosen and remove the two machine screws holding the switch to the electrical box, using a Phillips screwdriver and pull the switch out of the box. Loosen the two terminal screws on the side of the switch and pull off the wires. The ends will be formed into hooks, and it's OK to leave them that way as long as there is at least 1/2 inch of bare wire exposed on the end. Loosen the green ground screw on the bottom of the switch and pull off the bare ground wires.
If the ends of the black wires are damaged or there isn't enough bare wire showing, straighten the ends of the wires and then use wire strippers to remove enough insulation to expose 1/2 to 1 inch of bare metal.
3. Connect the Black Wires
For a simple switch (not a three-way), the black wire from the line cable can be attached to either of the switch terminals, but to make it easier to identify in the future, it's a good idea to connect it to the top terminal as long as you know which is the line wire. If you don't, there's no need to check because the switch will work just as well either way. This is also true if one of the wires is black and the other is white wrapped with black tape.
If you had to straighten the wires to strip them, make a clockwise hook in the end of the wire. If the hook is clockwise, the wire will tighten around the screw when you drive the screw back in. If you make the hook in the opposite direction, the wire will pop out from behind the screw and make a bad connection.
When installing a dimmer switch with wires instead of screws, twist each of the black wires on the switch together with one of the black wires in the box and screw a wire cap onto each connection.
4. Check the White Wires
When wiring a simple switch, the white wires bypass it, so they will be twisted together and capped. You don't have to change anything, but it's a good idea to unscrew the cap, make sure the wires are securely connected, and then screw the cap back on tightly.
5. Connect the Ground Wires
Connect the bare ground wires, which should already be twisted or clamped together with one wire longer than the others, to the ground screw and tighten down the screw.
6. Attach the Switch to the Electrical Box
Push the wires into the electrical box, align the holes on the top and bottom with those on the electrical box and drive machine screws to hold it. You can reuse the screws you removed when you took the switch out. Set a cover plate over the switch and secure it with the screws provided.
7. Turn the Power Back On
Flip the circuit breaker back on and test the switch.
Need a visual aide? Sparky Channel's demonstration will walk you through step-by-step: