What are Three-way Switches?

Three-way switches seem to be this mysterious device that no one can quite figure out. It's like it magically does things that no other switch can do. Although it has unique qualities about it, understanding how they work isn't all that hard when you understand what each terminal is and what it is used for. The key is to connect the right wire to the right terminal. If you wire three-way switches wrong, you'll be scratching your head in wonderment for a long time.

When you need to control a light from more than one location then three-way switches are the answer. By feeding the first switch with power to the common connection and feeding through the two traveler wires between the two switches, a light can be controlled in two locations. The position of the first switch chooses either one traveler wire or the other to feed power across to the second switch. Then, depending on the position of the second switch, the power may be fed through the common connection to the light.

By having two switches to control the lighting, you can turn the light on when you walk into the room from one direction and shut the light off at the other end of the room when you leave it. If you've ever stubbed your toe shuffling around in the dark, you know what I mean. That's all fine and dandy, you say, but what terminal goes where? Can I hook it up wrong? What are the common mistakes that people make?