HomeImprovementWeb.com, Easy-Do-It-Yourself-Home-Improvements.com, FamilyHandyman.com, Electrical-Online.com and Users.Wfu.Edu.com have online diagrams available for multiple three-way light switch configurations. Wiring diagrams available include wiring two switches through one box, two switches with power through the light, multiple switches through the light, multiple switches through each switch and end-of-run lights controlled by multiple switches.
Three-way switch wiring is typically more complex than that required for a simple single-pole on and off function. Most variations require a three-wire cable. Usually the wires are colored red, white and black, with the white wire being neutral, the black wire being hot and the red wire being the switch wire. Some configurations, however, require four wires to complete the necessary circuit. All configurations should also contain an additional ground wire for safety requirements.
Most illustrations are based on the use of nonmetallic sheathed cable, typically referred to by the brand name Romex. Calculations for the correct amount of wire needed should include the measurements between the light source, switch locations and the electrical supply, with an extra 20 percent added to the total for connection junctions. Wiring requirements depend on local building codes, but typically, 12-gauge wires are acceptable for most residential, indoor-wiring applications. Most building codes require that a connection must be made inside of a switch, receptacle or a junction box.