The purpose of an electrical switch is to open and close an electrical circuit in order to allow power to flow through the appliances and lights in your home. There was a time when electrical switches were as simple as having a little toggle you turned on and off. With advancements in technology and the need to be energy efficient, the number of different types of light switches on the market for you to consider has grown.
A single pole switch is the most common type of household switch. It is equipped with just two terminals and has just two purposes which are to turn the power on or off.
The number of poles a switch has indicates how many inputs the switch has. Another way to understand this is the number indicates the number of signals that can be switched to. A double pole switch is similar to a single-pole because it also has both on and off functions. However, it comes equipped with a four brass terminal instead of the two terminals a single pole switch has. This allows it to switch two hot wires whereas a single-pole switch can only switch a single hot wire.
Three-way switches will have the ability to turn off and on from two locations. The switch will have three terminal screws with the hot wire attached to the darkest screw terminal for common and marked as COM. The other two leads are used to wire up the switch. The switch will have the green screw for a ground terminal. When you replace the old switch, be sure to mark the common (COM) wire, so they do not get mixed up in the process. These switches must be used in pairs, and you cannot use any other type of switch in a three way application.
The four-way switch can control a light or an outlet from three separate locations with the use of two three-way switches. It will not have the on and off markings the other switches have. If you want to have more than three locations, you will need to use two three-way switches (one on each end). You would also use three four-way switches between the two three-way switches. It seems a bit confusing, but an electrician would be able to help set it up properly for you.
For more information, talk to a professional like Williams Electric Supply.