Non-resettable device which is fusible resin thermal-element for the safety protection , in normal working conditions, Thermal-element compress spring to make contact with osulatory point and osulatory slice, The circuit is closed through osulatory slice and shell contact, When the ambient temperature rose to a designed temperature, The thermal-element  begin melting and spring relax, The osulatory point and osulatory slice have been separated. This circuit has been permanently cut off