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Three-way switches control lights and receptacles from two points: for example, a light in the hallway that can be operated from the first floor and second floor. Three-way switches require a three wire cable: the power wire, the neutral wire, and the traveller or switch wire. The cable should also have a ground wire, or a total of four wires in the cable. The system also requires three-way switches.
The switches are wider than regular single-pole switches and they have three terminal screws on the side of the switch housing. Two terminals will be on one side of the switch housing; one terminal on the other side. It is advisable to use No. 12 wire for residential, indoor wiring. No. 14 wire is acceptable if the circuit is protected at 15 amperes. Local codes should be checked before starting any project.
Use non-metallic sheathed cable known as Romex. To figure materials needed, measure the distance between the new switch and the power source. Add an extra foot for every connection you will make along the line. Then, to provide a margin for error, add 20% more.
For example, if you measure 12 feet of cable between a new switch and existing fixture, add another 2 feet for the two connections, making a total of 14 feet. Then add 20%, about 3 feet, to the total. To do this job, you will need 17 feet of cable.
To make wire connections, the wire must be pulled through boxes at least 6 inches, cut, and then stripped of insulation. Here is the procedure to follow:
Cut the cable to the proper length using lineman's pliers or a hacksaw. With a sharp knife or sitting tool, slit the outer sheathing, being very careful no to cut the insulation covering the wires inside the cable. If possible, you may also use a cable ripper.
Peel back the sheathing and trim it square. With wire strippers, put single wires in the proper size groove in the handle. Twist the stripper or rotate it 360 degrees, sliding the insulation off the wire as it breaks loose under the cutting blades. Remove 3/4 to 1 inch of insulation. Splice wires together and top with a wire connector.
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