The double-pole switch is similar to its little brother, the single-pole switch.
The single- pole switch breaks one circuit (the hot wire). The double-pole switch breaks two circuits (two hot wires)(or one double pole circuit).
The double pole switch is most commonly found on circuits of 240 volts or higher.
They are often used to switch 240 volt receptacles and appliances. Because of this you must ALWAYS turn off the power when replacing one.
There's an easy way to identify the double-pole switch. It has four screw terminals and the "off" "on" marking written on the handle. Although it looks like the four-way switch, the four-way switch does not have any "off' "on" markings. (Four-way switches do not operate the same as a Double-pole switch).
Dimmer switches are designed for incandescent lights only. However, there are some specialty dimmers on the market for specific purposes. For the sake of this article we will only talk about the incandescent dimmer. One of the most important things to remember about dimmers, is their capacity is rated in watts. So you need to know how many watts you are going to be dimming. For example, if your dinning room light is a total of 800 watts, you can't use a dimmer rated for 600 watts. You must always use the correct size rating.
However you can always size up. In other words, if you have say 600 watts of light, then you can use an 800-watt dimmer.
The Singe-pole dimmer is the same as a single pole switch. It gets wired the same and works the same, all except the dimming part. The dimming is accomplished by varying the resistance of the load inside the dimmer switch.
The three-way dimmer works the same as single-pole dimmer, with these exceptions.
The three-way dimmer is wired the same as a three-way switch. That is to say it has a common terminal, and two traveler terminals. (Most likely you will find pigtails and not screw terminals)(Pigtails are short pieces of wire) But the big difference is you only use ONE DIMMER per three-way circuit. For example, if you have a switch at both doorways in your dinning room, and you want to install a dimmer, you will only replace one of the existing switches with the dimmer, the other switch will remain
a standard three-way.