Tripping device for an electrical switching unit and electrical switching unit including such a tripping device

A thermomagnetic trip assembly for an electrical switching unit said assembly comprising:

• a thermal trip,
• a magnetic trip, and
• a tripping arm intended to be mechanically coupled to a switching mechanism of the electrical switching unit, said tripping arm comprising first and second actuation levers;
• the thermal trip comprising a bimetal strip that is capable of deforming when the current passing through it exceeds a first predefined threshold;
• the magnetic trip comprises a movable armature, a fixed armature and an electrical conductor;
• the movable armature being capable of moving from a first position, wherein the movable armature is distanced from the fixed armature, toward a second position, wherein the movable armature is in contact with the fixed armature at contact areas, when the current which flows through the electrical conductor exceeds a second predetermined threshold, the movement of the movable armature toward the second position actuating the second actuation lever;
• the electrical conductor and the bimetal strip being electrically connected in series with one another between first and second connection terminals of the trip assembly;
• the movable armature is connected to the first connection terminal, and in that wherein the fixed armature is connected to the second connection terminal,
• and in that wherein the respective contact areas of the fixed armature and of the movable armature are made of electrically conductive materials that exhibit a low degree of mutual weldability.