Three-phase thermal protector

A three-phase thermal protector comprising:

• a) a hermetic receptacle comprising a cover formed of a metallic material and having an opening the width of which is larger than the depth of the cover, and a header plate hermetically secured to an opening edge of the cover and having two through-apertures;
• b) two electrically conductive terminal pins inserted through the respective through-apertures of the header plate, each terminal pin being hermetically secured in each through-aperture by an electrically insulating material filling a space between the peripheral wall surface of each aperture and the outer periphery of each terminal pin, each terminal pin having an end placed in the interior of the hermetic receptacle and a fixed contact electrically conductively connected to the end;
• c) two fixed-contact supports formed of an electrically conductive material and disposed in the receptacle so as to be substantially parallel to the header plate, the fixed-contact supports having one portions coupled to the terminal pins respectively and one ends on which fixed contacts are disposed respectively;
• d) an electrically insulating reinforcement member interposed between the header plate and the fixed contact support for reinforcing the fixed-contact supports;
• e) an operating temperature calibrating plate formed of a metallic material and disposed in the receptacle, the operating temperature calibrating plate having an end side secured to the cover of the receptacle by way of welding and a suitable portion more bendable than the other portion thereof;
• f) a thermally-responsive-element support having one of two ends secured to the operating temperature calibrating plate and a cutout portion at a suitable portion thereof, the thermally responsive-element support being elastically deformable easily in a direction intersecting perpendicularly to a plane thereof;
• g) a thermally responsive element having a supported end secured to the other end of the thermally-responsive-element support and a generally central shallow dish-shaped portion reversing its curvature with a snap action at predetermined temperatures, the thermally responsive element carrying two movable contacts on respective portions thereof substantially symmetrical about a central line passing through the supported end so that the movable contacts are operatively associated with the respective fixed contacts;
• h) a protrusion fixedly disposed on the header plate so as to be positioned between the thermally responsive element and the header plate, the protrusion having a distal end in contact with a portion of an underside of the thermally responsive element away from the central portion thereof toward the supported end, the portion of the thermally responsive element in contact with the distal end of the protrusion acting as a fulcrum;
• and
• i) a push projection provided on the operating temperature calibrating plate so that a distal end thereof extends through the cutout portion of the thermally-responsive-element support, the distal end pushing a convex side of the thermally responsive element at a room temperature, in the vicinity of a portion thereof on which the center line passes through the supported end such that a pushing force of the push projection is dispersed equally to the distal end of the protrusion and the fixed contacts, the push projection being moved with movement of a free end of the operating temperature calibrating plate upon displacement applied to the cover of the receptacle for calibration of an operating temperature.