BREAKER, SAFETY CIRCUIT, AND SECONDARY BATTERY PACK

To provide a breaker capable of suppressing generation of cutting powder when welding a case.SOLUTION: A breaker 1 includes a movable piece 4 that includes a fixed contact 21, an elastic portion 44 that is elastically deformable, and a movable contact 41 at one end of the elastic portion 44, and presses the movable contact 41 against the fixed contact 21 to make contact with the fixed contact 21, a thermally responsive element 5 that changes the movable piece 4 from a conducting state in which the movable contact 41 is in contact with the fixed contact 21 to an interrupted state in which the movable contact 41 is separated from the fixed contact 21 by deforming with a change in a temperature, a case body 7 having a housing recess 73 for housing the fixed contact 21, the movable piece 4 and the thermally responsive element 5, and a lid member 8 fixed to the case body 7 and covering the housing recess 73. The lid member 8 includes an embedded portion in which a part of the movable piece 4 is embedded, and a first recess that is depressed in a thickness direction of the lid member 8. The case body 7 includes a first protrusion that is fitted into the first recess.SELECTED DRAWING: Figure 1 【課題】ケースの溶着時に切削粉の発生を抑制できるブレーカーを提供する。【解決手段】ブレーカー１は、固定接点２１と、弾性変形する弾性部４４及び該弾性部４４の一端部に可動接点４１を有し、可動接点４１を固定接点２１に押圧して接触させる可動片４と、温度変化に伴って変形することにより、可動片４を可動接点４１が固定接点２１に接触する導通状態から可動接点４１が固定接点２１から離隔する遮断状態に移行させる熱応動素子５と、固定接点２１、可動片４及び熱応動素子５を収容する収容凹部７３を有するケース本体７と、ケース本体７に固着されて収容凹部７３を覆う蓋部材８とを備える。蓋部材８は、可動片４の一部を埋設する埋設部と、蓋部材８の厚さ方向に陥没する第１凹部を有し、ケース本体７は、第１凹部に嵌め合わせられる第１凸部を有する。【選択図】図１