Electromagnetic trip device with tripping threshold adjustment

An electromagnetic trip device for an electrical protective device, with adjustment of the instantaneous tripping threshold, comprising a yoke presenting a lower face and an upper face, a movable plunger core movable axially across an orifice arranged in the upper face, a coil fitted between said faces and arranged around the movable core, a stationary core securedly fixed to the lower face of the yoke, a return spring urging the movable core in the opposite direction from the stationary core, a magnetic circuit comprising said yoke, the movable core and the stationary core and having a first air-gap defined between the movable core and the stationary core, an adjustment device of the position of the movable core between a maximum separation position from the stationary core and a minimum position and an annular groove provided in said movable core over a greater axial distance than the axial distance between said maximum and minimum positions, in the zone of said upper face, in such a way that the latter is in proximity to a first edge of the groove in one of said positions and in proximity to the a second edge of the groove in the other of said positions, a second air-gap defined between said upper face and said first edge and a third air gap defined between said upper face and said second edge.