A thermal overcurrent circuit breaker having a switch housing in which a thermal expansion element and a snap-action switching mechanism, which is coupled to the thermal expansion element and can be manually operated, and also a moving contact, which interacts with the snap-action switching mechanism, and a fixed contact are arranged, the fixed contact being connected to a first connection rail while contact is made with the moving contact by a second connection rail by means of the thermal expansion element. The switch housing has a number of connection chambers in which in each case one of the connection rails is arranged, wherein a two-limb spring element for making clamping contact with a connection line, which is guided into the connection chamber via a first housing opening and has the connection rail, is arranged in each connection chamber.