The voltage in the university dormitory is 220 volts. Generally, the dormitory is limited to less than one kilowatt, and each school is different. Limit the current by installing an air switch. If the dormitory voltage is installed at 3 A, then 220×3=660 watts, that is, the power is limited to 660 watts, and it will trip if it exceeds; 220×4=880 watts, if 4 amps are open.