Electronic overcurrent release for circuit breaker, comprising - a current transformer, whose primary side is in each case linked to one of the phase currents (11, 12,13) to be switched and whose secondary side is in each case connected via a rectifier arrangement to a load resistor; - a micro-controller with measurement inputs (41... 43), which are each operatively connected to one of the load resistors, and have a signal output which is operatively connected to an electromagnetic actuator; - a first adjustment means for selecting a suitable rated current value connected to at least one set input (50... 53) of the micro-controller, wherein the rated current value is selectable in a range between a minimum rated current value and a maximum rated current value; - a second adjustment means for selecting a suitable degree of inertia connected to at least one set input (50... 53) of the micro-controller, - voltage supply means connected to the rectifier arrangements for supplying the electronic components including the micro-controller, - wherein a specific overcurrent tripping characteristic is mapped in the micro-controller depending on the selected setting of the first and second adjustment means (S1, S2), and where a trip signal is present at the trip signal output for activating the actuator for switching off a circuit breaker which can be connected to the overcurrent release, when the magnitude and time of this characteristic are exceeded by at least one of the phase currents (11, 12, 13) characterised in that - the second adjusting means is additionally provided with a test position, and - a fixed test current value below the minimum rated current value and a fixed test delay time are mapped in the micro-controller when the test position is selected, and a trip signal is present at the trip signal output when the test current value is exceeded in magnitude and time by at least one of the phase currents (11, 12, 13) - a current transformer, whose primary side is in each case linked to one of the phase currents (11, 12,13) to be switched and whose secondary side is in each case connected via a rectifier arrangement to a load resistor; - a micro-controller with measurement inputs (41... 43), which are each operatively connected to one of the load resistors, and have a signal output which is operatively connected to an electromagnetic actuator; - a first adjustment means for selecting a suitable rated current value connected to at least one set input (50... 53) of the micro-controller, wherein the rated current value is selectable in a range between a minimum rated current value and a maximum rated current value; - a second adjustment means for selecting a suitable degree of inertia connected to at least one set input (50... 53) of the micro-controller, - voltage supply means connected to the rectifier arrangements for supplying the electronic components including the micro-controller, - wherein a specific overcurrent tripping characteristic is mapped in the micro-controller depending on the selected setting of the first and second adjustment means (S1, S2), and where a trip signal is present at the trip signal output for activating the actuator for switching off a circuit breaker which can be connected to the overcurrent release, when the magnitude and time of this characteristic are exceeded by at least one of the phase currents (11, 12, 13) - the second adjusting means is additionally provided with a test position, and - a fixed test current value below the minimum rated current value and a fixed test delay time are mapped in the micro-controller when the test position is selected, and a trip signal is present at the trip signal output when the test current value is exceeded in magnitude and time by at least one of the phase currents (11, 12, 13)