A main switch is a central cut-off switch that controls the smaller cut-off switches and machines of a building. The main switch can be cut off by a human or a computerized system to control the flow of power in the building.
The main switch, also referred to as a distribution board, divides the feed of electrical power to a building into subsidiary circuits and provides a protective fuse for each circuit. When a circuit is overloaded, the fuse at the main switch is popped. This effectively stops power from flowing through the circuit and prevents fire from the overload. Without the main switch, an overload would cause current to heat the wire, melt the insulation and eventually start a fire.