Abstract: An autotrip plunger of a circuit breaker is disclosed for opening contacts of the circuit breaker to install and uninstall the circuit breaker from a current source. In an embodiment, the autotrip plunger includes a compression spring, a first body section and a second body section, the first body section including a contact surface for contacting a tripping element of the circuit breaker and the second body section including an arbor shaft for fitting in the compression spring. At the free end of the arbor shaft, the arbor shaft includes at least one radial protrusion for holding the compression spring. A circuit breaker with such an autotrip plunger is also disclosed.