subject: General Facts About Wiring Three Way Switches: [print this page] The difference between a standard switch and a three way switch is one additional terminal,or connection. A 3 way switch has 2 terminals that are either silver or brass coloured and one terminal that is dark coloured.
The silver or brass terminals are known as travellers or messengers and the dark colored terminal is known as the common. In case all three terminals appear similar in color, the common terminal will be then marked by the word "common" engraved on the back of the switch.
The arrangement of these terminals on the switch can vary as it depends upon the manufacture. So it is better to in check advance to ensure proper identification of the common terminal. In a three way switch circuit there are two 3 way switches and a light or series of lights which are regulated by these switches.
Since the basic purpose of each switch is to turn the lights on or off the system is organized in such a way that both the switches can communicate with each other. This function is carried by one of the two travellers or messengers and for this reason the two travellers or messengers are always interconnected regardless of whatever is mentioned in the configuration diagram for wiring the switch. You should also trace the white and red conductors of the 3 conductor wire.
As the travellers or messenger terminals are always interconnected, the common terminal is the only one left. To understand this terminal, consider for a moment a standard switch that has only 2 terminals. When wiring a standard switch the incoming power feed (hot) conductor is connected to one terminal (usually bottom right) and the outgoing power feed to the lights is connected to the other terminal (usually top right).
This is also the purpose of the common terminals in a 3 way switch circuit. For one of the two 3 way switches you connect the incoming power feed (hot) conductor to its common terminal and the other of the two 3 way switches the outgoing feed to the lights is connected to its common terminal. You must also note that the white conductor in the 3 conductor wire (red, black and white) connected between the two switches is not a neutral. Either the red or the white terminal will be hot but this depends on the on/off position of the switches.
