You can turn the lights on here and off over there, and you can do it yourself once you know the trick. It's not exactly simple, but it's far less complicated than most people assume.

There are two important things to remember to make 3-way switches work right. One is that three-way switches are really single-pole, double-throw devices. That means that one of the three terminals on each switch is always connected to one of the other two. The terminal that is always connected is called the point terminal. It should be specially identified. Most commonly, the screw for the point terminal will be dark and the other two screws will be bright. Toggling - flipping - a 3-way switch changes which of the other two terminals the point terminal is connected to.

To help visualize this, you can think of a 3-way switch as a "V." Think of the bottom of the "V" as the point terminal; the top of the letter is where the other two terminals are. Each time the switch is flipped, the wire terminated on the point is disconnected from one of the other two terminal screws and connected to the other.

The other important thing to remember is that 3-way switches work in pairs. It takes exactly two of them to make a 3-way system work properly. Three-way switching works because the two non-point terminals on one of the 3-way switches are always connected directly to the two non-point terminals on the other 3-way switch with a pair of wires called the travelers. A three-conductor cable - with or without a ground wire - connects the two switches and carries the two travelers. The third insulated conductor in the three-conductor cable is used as a neutral or as a hot wire, depending on which is needed.

In every 3-way switch system, the ungrounded conductor from the panel - the hot wire - is connected to the point terminal on one of the two switches. The switch-controlled hot wire, which connects the switch system to the first controlled light, is connected to the point terminal on the other switch. The grounded conductor - the neutral wire - is not switched. It is carried to the first light and connected there. If your wiring includes an equipment grounding conductor - a ground wire - it should be bonded to each switch, to any metal box the wiring goes through, to each switch and to each light fixture.

There are three scenarios that cover more than 90% of all three-way switch installations. They are described in the articles linked below. One of these should work for you in any new installation. If you're troubleshooting existing wiring, one of these three setups will also most likely be the one you're looking at.

Remember to turn the power OFF at the panel before starting. For a new installation, remember to use #12 AWG (American Wire Gauge) wire on a 20 amp circuit. You can use #14 AWG wire on a circuit protected at 15 amps.

More:

• Basics of Installing 3-way switches
• Power fed to one switch, light fed from the other
• Power feed and light feed in the same switch box
• Power at the light