Single and dual pole are two types of wall switches. They both control a light or device from a single location and look almost identical when the switch face plate is on but they function differently.
Single Pole Switch
A single pole switch has two screw terminals, one at each side, which are wired to the hot wire. When wired properly, a hot circuit wire is attached to each of the terminal, one for the incoming wire and the other is for the outgoing wire back to the device. Some single pole switches may come with a ground terminal but not all of them do.
Double Pole Switch
As its name implies, the double pole switch has two screw terminals on each side, double than the single pole ones. For this reason, it can handle switching two hot wires at the same time which allows it to switch a 240 volt circuit. Double pole switches always come with a ground terminal.
Single and Double Pole Switches Uses
While double pole switches can handle to switch a 240 volt circuit, single ones cannot. Therefore, double pole switches are the ones needed to be installed when wiring certain appliances that require 240 volts.