A float switch is a device used to detect the level of liquid within a tank. The switch may be used in a pump, an indicator, an alarm, or other devices. When used in a typical sump pump application, the float switch is used to turn an electric pump on and off. As water enters the reservoir of the sump pump, a plastic float begins to rise. The float is commonly fastened to a rigid structure at one end, thereby, causing the float to pivot or roll over as it sises on the water level.

A micro switch inside of the float switch is connected to an electric pump by wiring that runs through the chassis of the pump. Once the proper angle is reached by the float, the ball inside runs to the low side of the switch and completes the circuit, allowing electricity to reach the pump motor and begin to pump the water out of the basement or structure. Once the water has been pumped out of the reservoir and the float reaches its resting level once again, the ball flows out of the switch and the contact is broken within the wiring harness, turning off the pump motor. In this design, the float switch is commonly housed in a copper, aluminum or tin float canister to prevent rust and deterioration in the submerged position.