Turning the lights on and off in a house is as easy as "flipping a switch." But did you know that not all switches are the same? They can have a different number of terminals and voltage capacity. The most common toggle switches used for lighting are the single-pole switch and the three-way switch.
Single pole switches have on and off markings on the toggle. It has two brass-colored screw terminals for the hot wires, where one terminal is for the power source, and one terminal is for the load (fixture). The easy thing about these switches is that the brass-colored terminals are interchangeable. Therefore, one can connect the load and power wires to either terminal. However, wiring both to the same terminal would not make the switch functional. Also, most single-pole switches have a green grounding terminal.
The difference between a single pole and a three-way switch is the number of terminals and on/off markings. Three-way switches do not have on and off markings on the toggle because the two different positions on the toggle divert the power source between the two loads. There are four terminals on the switch - one green, one black, and two brass. The green terminal, like the single-pole switch, is for grounding the switch. The power source is connected to the black terminal known as the common, labeled as "COM." Finally, the two brass-colored screw terminals for connection to the travelers or loads.
There are many other kinds of toggle switches based on the number of poles and throws used for different applications. The poles are the number of power circuits, and throws are the number of states to which the current can pass through the switch. The single pole switch mentioned above is a single pole single throw (SPST) since there are one power supply and one circuit. And the three-way switch is a single pole double throw (SPDT), one power source with two throws. The naming convention continues with the number of poles with the number of throws (#P#T).
When it comes to lighting, the single pole and three-way switches are the most common toggle switches. Knowing the basics of switch terminals helps people to understand the basic wiring schematics for different applications such as lighting and device control.
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