Each dormitory building of Hunan University of Science and Technology has a separate master switch to protect the circuit safety. A switch is a circuit switching device used to cut off the circuit. The working principle of leakage protection switch is that there are two groups on one iron core: input current winding and output current winding.

When there is no leakage, the input current and the output current are equal, and the vector sum of the two magnetic fluxes on the iron core is zero, so the potential will not be induced on the third winding, otherwise the voltage will be induced on the third winding, which will drive the actuator after amplification and trip the switch.