A two-way light switch produces light when two of three wires transport a current to either end of the installation. The third wire creates repetitive switching at either end. The red wire is the traveler that carries the current from one switch to another. The two black live cables switch power into the circuit, and the green cable is the ground cable that is wired between the devices.
A two-way switch allows lighting to be controlled from multiple locations. This type of switching is useful for apartments, hotels or other large buildings. A series of lights in a large room, stairwell, or hallway can be controlled with one switch. This saves time and energy for the user and ensures that all lights in an area are turned on or off when needed.
Three-way and four-way lighting systems exist for larger areas that include more than two light sources. The set-up of each type of light switch requires basic electrical knowledge. Users must know how wires cross and work together to create simultaneous lighting. Even if one wire is not connected properly, the whole system does not work. The installation of the system requires a thoughtful and organized plan of wire connection.