There are many types of switches, just as there are many types of receptacles. You may easily be confused as to which switch is needed for what purpose. Listed below are common household switches and their uses (Fig. 1).
1.
A Single-Pole Switch
The most common switch in a house is a single-pole or single-throw switch. Single pole means there is only one place for the switch to connect--in other words, one click sends the power to one place. A single-pole switch has two side screws. When the switch is in the OFF position, it's an open circuit. When you throw the switch ON, the movable switch comes into contact with a fixed contact, closing the circuit. The voltage that was sitting on one screw can now zip through the switch and turn on your light.
2.
A Double-Pole Switch
A double-pole switch is nothing more than two single-pole switches that are side by side. Even though both are on one body, they are not connected internally. This switch is used when you want to connect two voltages to power one load. This type of switch is normally used in 240-volt circuits because these circuits need two phases--two hot legs. A double-pole switch can simultaneously connect both sides of a circuit to an appliance.
3.
A Three-Way Switch
A three-way switch looks almost identical to the single-pole switch but differs internally. It has an extra screw called the COM or "neutral" screw. The label, COM, stands for "common" and is written next to the screw, eliminating any doubt. If you need a light to work from two locations, you use a three-way switch. In a three-way switch, whatever routing wires are connected to the COM terminal are also connected to either of the other two screws. In one position the COM terminal routes the circuit to one of the two other terminals. If the switch is thrown again, the first circuit opens the COM to connect to the other screw. Throw the switch again and the circuit returns to its original position.
4.
A Four-Way Switch
A four-way switch looks almost identical to a double-pole switch but there are two big differences. First, and most noticeably, is that no OFF and ON is written on the switch. Second, a four-way switch connects internally in an X pattern. In one position, the upper left screw will be connected to the bottom left screw, and the upper right screw will connect to the bottom right screw. When throwing the switch again, the upper left screw will connect to the bottom right screw and the upper right screw will connect to the bottom left screw. This is the X pattern. This type of switch is used with 2 three-way switches. It allows a circuit to be turned on or off from three (or more) locations.
