A mechanical circuit breaker unit for interrupting a line includes a contact arrangement and an electromagnetic drive. The contact arrangement has first and second fixed contacts and a guided moving contact. The electromagnetic drive moves the moving contact. The separating unit can assume a first state and a second state. No electric connection exists between the first and second fixed contacts in the first state. The moving contact electrically connects the two fixed contacts to each other in the second state. The separating unit can be transferred from the second state into the first state by moving the moving contact. The second fixed contact has a recess for receiving the moving contact, and the moving contact engages at least partly into the recess when the separating unit is in the first state.