How Does a Three-Way Light Switch Work?

How Does a Three-Way Light Switch Work?
How Does a Three-Way Light Switch Work? (Image: "Light Switch." [Online image] Available http://knol.google.com/k/larry-angell/how-to-wire-a-3-way-light-switch/3jvoj4lrdx285/2#, 25 April 2009.)

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How a Light Switch Works

To understand how a three-way light switch works, you must first understand how a normal two-way switch works. A regular light switch runs power to the light bulb to turn it on and then returns it to the switch, making a complete circuit. This is accomplished through the use of Romex wire, which has a black and white wire inside it as well as a bare wire that provides the ground wiring. The black and white wires are what make the light switch work. The black wire carries the electrical current from the switch, after it has been turned on, to the light bulb. The bulb lights up and the current travels along the neutral white wire back to the switch. Then the cycle starts over again.

How Wiring in Switches Works

The wiring is also an important part of the three-way light switch. A two-way light switch, like most found in your home, have two terminals inside them. One terminal connects the black wire to the light bulb, and the other connects the white wire from the light bulb back to the light switch. When the light is turned off, the terminals are no longer connected and the circuit is broken. When the light is turned back on, the terminals and wires become connected again and the current can flow to light up the bulb.

How a Three-way Light Switch Works

A three-way light switch allows one light to have two different light switches, often in two different rooms for convenience. The three-way switch has three terminals inside it instead of two. The switch can connect to either terminal. When both switches are connected to the same terminal, then it completes the circuit and turns the light on. Either of the switches can be flipped to break the circuit by connecting a switch to the opposite terminal. To turn it back on, either that switch can be flipped so it connects to the terminal again, or the other switch can be flipped so they are both connected to the same terminal, except on the other side this time. The switches are wired with a special type of wire that has a red wire in addition to the black and white wires. This red wire connects the three-way switches so the circuit has a complete path to flow through and both light switches can control one light.

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