Protective device of three-phase motor

A protector for a three-phase electric motor, comprising:

• a hermetic container including a housing made of a metal and a metal plate hermetically secured to an open end of the housing;
• a protrusion provided in the housing;
• three conductive terminal pins inserted through three through holes formed in the metal plate and hermetically fixed by an electrically insulating filler respectively;
• three fixed contacts secured to ends of the conductive terminal pins protruding into the hermetic container respectively;
• a thermally responsive plate formed into a dish shape by drawing so as to reverse a direction of curvature at a predetermined temperature;
• three movable contacts which are secured to the thermally responsive plate so as to be opposed to the fixed contacts respectively, thereby constituting three pairs of switching contacts together with the fixed contacts;
• an elastic member holding a central part of the thermally responsive plate between the protrusion and the elastic member, thereby biasing the thermally responsive plate in such a direction that the thermally responsive plate departs from the fixed contacts;
• and
• a rotation preventing member which prevents the thermally responsive plate from rotation about a central part of the thermally responsive plate, thereby maintaining the movable contacts in an opposed state with respect to the fixed contacts respectively,
• wherein the conductive terminal pins are terminals located at a neutral point side of phase windings of the three-phase motor respectively in use of the protector, so that an AC current flowing into the three-phase motor is interrupted.