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A switch is an on-off device connected to the live wire in order to control the current in an electric circuit. Two commonly used types of switches are a single pole and double pole switch.
The switch used in an appliance to start or stop the flow of current in it is single pole switch whereas the main switch at the distribution board, used to switch on or off the mains is the double pole switch. The dual control switch used in the staircase wiring is a special kind of double pole switch.