The trip unit (10) according to the invention is capable of being connected to a circuit breaker and includes a first block (12) and a second block (14). The first block (12) comprises a first case (16) and a circuit breaker trip member (20) accessible from outside the first case (16). The second block (14) comprises a second case (26) and at least one member (28) for detecting an electric fault. The first block (12) and the second block (14) are two distinct blocks relative to one another and the first case (16) and the second case (26) are capable of being mechanically assembled to one another in an assembled configuration of the trip unit (10). Each contact end (62) is capable of mechanically cooperating with the trip member (20), when the corresponding detecting member (28) detects an electric fault.