Breaker and safety circuit equipped with the same

A breaker comprising:

• a fixed piece which has a fixed contact,
• a movable piece which has a movable contact and which presses the movable contact against the fixed contact to make contact therewith,
• a thermally-actuated element which deforms with a change in temperature so as to shift the movable piece from a conduction state in which the movable contact contacts the fixed contact to a turn-off state in which the movable contact is separated from the fixed contact,
• a positive temperature coefficient thermistor which provides an electrical conduction between the movable piece and the fixed piece when the movable piece is in said turn-off state, and
• a resin case which accommodates the fixed piece, the movable piece, the thermally-actuated element and the positive temperature coefficient thermistor,
• wherein:
• the fixed piece has a support portion for supporting the positive temperature coefficient thermistor, the support portion comprises a plurality of protruding contacting portions contacting the positive temperature coefficient thermistor,
• the resin case has a bottom surface provided with a concave portion which is concaved toward the positive temperature coefficient thermistor across the fixed piece, and
• in a planar view when the fixed piece is viewed from the positive temperature coefficient thermistor, said plurality of protruding contacting portions are each disposed within the concave portion,
• the concave portion has a bottom which is recessed from the bottom surface of the resin case so as to prevent the bottom of the concave portion from protruding outwardly from the bottom surface of the resin case when the thermally-actuated element is deformed and presses the positive temperature coefficient thermistor, and the positive temperature coefficient thermistor presses the plurality of protruding contacting portions toward the bottom surface of the resin case, and
• between the bottom of the concave portion and the bottom surface of the resin case, a step is formed so as to extend over the substantially entire circumference of the concave portion,
• the bottom of the concave portion is formed by a surface of the fixed piece which is on an opposite side of the plurality of protruding contacting portions of the support portion and which is exposed from the concave portion,
• the bottom surface of the resin case is provided with a terminal piece comprising terminals configured to be connected to an external circuit so as to be exposed from the bottom surface of the resin case, and
• the concave portion is provided, in vicinities of the terminals, with arc-shaped portions which are convex toward respective terminals.