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Three-way Switches

What are Three-way Switches?

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Three-way Switches Labeled

Three-way Switches Labeled

Photo: Timothy Thiele

Although we've all heard the term three-way switches, what do we really know about them? OK, they're switches that turn lights on and off, that's obvious. But what makes them so special? Does three-way mean they can be installed three different ways? Funny, but no. Three-way switches are specially designed to work in pairs and often in combination with four-way switches to control lighting from more than one location.

Terminals on Three-way Switches

Three-way switches come equipped with four terminal screws for connecting wires. The green terminal screw is used to connect the ground wire. This terminal screw has either a green or bare copper wire connected to it.

As you look over the three-way switch you'll notice two brass-colored terminal screws. These are used to connect common wires between the two three-way switches. These are called traveler connections. Basically, if a black wire is hooked on one terminal and a red wire is hooked on the other, the other three-way switch would be wired exactly the same way. Depending on the switch position, one of these two wires will always be "hot" when power is "on" to the circuit.

The last terminal screw is a darker-colored screw. This is the common connection of the switch. Its purpose is to either be the feed source for the circuit or the switch-leg for the feed to a light fixture. As a feeder, the power come in through this connection and, depending on the position of the switch, the power goes out to the other three-way switch through one of the switch-leg (travelers) connections. On the other end, at switch number two, the feed come in through one of the traveler connections and out through the common connection. at this point, the common connection connects to the light fixture feed.

Three-way Switch Blunders

One of the most common problems with three-way switches is improper wiring. It's very easy to mix up three-way switch wiring when replacing a three-way switch. The most important thing you can do is to take time to mark the wires before you remove any wires from the old switch, The wire connected to the common connection is the most important to mark. It must always connect to the darkest-colored terminal screw. By placing a colored piece of tape or label on the wire, it will be easy to find when you connect the new switch

Another great idea is to only remove one wire at a time when replacing switches. That way, when you remove a wire from one switch, you can attach it to the new switch. By doing it one switch at a time, you'll be sure to properly connect the switch.

Making a Secure Connection

Three-way switches have different methods of connections depending on what brand you may use. They all have screws on the side, but some come with holes or slots to slide the wire into the switch. Still others come with a quick-mount, spring-loaded slot that holds the wire in place. It basically has two copper strips inside that are bent at an angle to allow the wire to go in, but not to come back out. Although this may be the quickest way to connect a switch, it is not recommended. Personally, I don't feel this is a solid connection. By screwing the wires down, you'll be sure to have a tight, safe, and secure connection.

Three-way Switch Troubles

Sometimes three-way switches go on the fritz. This can be caused by loose wire connections and faulty switches. By turning off the power to the circuit and removing the switches, you can tighten the screw terminal connections. Check the neutral connections and other connections made with wire nuts, or dare I say it, electrical tape. If you have one of these connections, replace it with a wire nut.

You may notice that the switch makes a sizzling or popping sound when you turn the switch on or when it is on. This means that the switch contacts are getting bad and aren't making good contact. This switch should be changed immediately to avoid bigger electrical problems. By inspecting your switches periodically, you'll ensure safe and effective electrical connections.

Want to learn more about switches? The following articles will help guide you. Select one below to continue learning about switches.

Rotary Switches
Learn what a rotary dimmer switch is and how it can benefit lighting in your home.

How to Change a Single-pole Switch
Find out how to change a single-pole switch with this step-by-step tutorial.

Anatomy of a Three-way Switch
Learn what a three-way switch is made of, how they work, and how they are connected.

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