Abstract: The trip device comprises a magnetic circuit having a first and second fixed parts, a movable element and an adjustment device. The adjustment device comprises a shunt and an air gap arranged between the first and second fixed parts branched off with respect to the mobile element. The tripping threshold of the trip device is modified by varying the air gap distance between the shunt and the second fixed part. In a circuit breaker, the mobile element acts on an opening mechanism and an adjustment part acts on the adjustment device making the air gap distance vary. A sensor associated to the magnetic circuit supplies a measurement signal to a processing unit.