The invention relates to a circuit breaker for electric supply lines, in particular energy lines or battery cables of motor vehicles. Said circuit breaker comprises a first connection element (2) and a second connection element (4), the current path running between the first connection element (2) and the second connection element (4), when the circuit breaker (6) is in a conductive state. The aim of the invention is to provide a cost-effective, fail-safe circuit breaker. To achieve this, the first connection element (2) comprises a cavity (8) and the second connection element (4) is configured from an electrically conductive flat part and the second connection element (4) has a projection (10) that corresponds to the shape of the cavity (8), in such a way that in the conductive state of the circuit breaker (1), the projection (10) rests in the cavity (8) in a non-positive fit.