Switches are used to operate lights, fans, and even large electric motors, but they're not all the same. It's important to pick the right type of switch for the application.
A single pole switch is used to control the light in a small closet or bathroom. It's called a single pole switch because there are two wires connected or separated by the switch mechanism. There's also a ground wire to protect against electrical faults.
In some applications however, such as hallways and larger rooms, having a single switch can be inconvenient, so it might be useful to control the light from two locations, and this is the role of the 3-way switch.
These are used in pairs, with one at each switching location. They are wired so either switch can work the light, regardless of the setting of the other.
A 3-way switch is larger than a single pole switch and has three screw terminals for wiring connections, plus a ground. Two of these take traveler wires that go from one switch to the other. For the third terminal, one switch is connected to the hot supply wire while the other switch is joined to the light.
Single pole and 3-way switches are used for low current 120VAC (Volts of Alternating Current) applications. Occasionally the circuit may be on a double pole breaker, making the circuit 240VAC. This circuit is typically used on a larger load like a motor or an appliance that requires 240VAC.
A double pole switch is used with a 240VAC electrical supply. In domestic applications these circuits power clothes dryers, electric ranges, electric hot water heaters or air conditioning window units, that are on a dedicated double pole breaker in your load center. 240VAC double pole switches require both 120VAC hot wire, which are usually a black and red wire connected to the switch. A third green wire is connected to the ground screw. The double pole switch breaks both wires of the 240VAC at the same time to open the circuit and closes at the same time to make contact and close the circuit.
When deciding what type of switch to use, you want to consider how you want your switch to function. Do you want to simply turn on/off a light in a single location? If so, a single pole switch is the best option to get the job done. Do you want to control the light at two locations? Then a pair of 3-way switches is a better option.
Here are a few things to consider when choosing your switch:
And remember to always ground your switch.
Interested in commercial specification grade switches? Learn more here.
Four types of electrical switches in the home. The Spruce. https://www.thespruce.com/types-of-electrical-switches-in-the-home-1824672
Understanding three way electrical switches. The Spruce. https://www.thespruce.com/three-way-switches-1152391