Protective apparatus for an alternating current electrical installation, having a first in connection terminal for a first electrical pole, a second in connection terminal for a second electrical pole different from the first electrical pole and an out connection terminal for the first electrical pole, each said connection terminal (22, 23, 26) being configured to receive a stripped end section of an electric cable or a tooth of a horizontal comb-like busbar; which apparatus comprises: - a first current conveying circuit between the first in connection terminal and the out connection terminal, comprising a fixed contact and a movable contact; - an actuation mechanism of the movable contact having two stable positions, respectively a cutting-off position in which the movable contact is away from the fixed contact and an engaging position in which the movable contact bears on the fixed contact; - a lever to act manually on the actuation mechanism in order to pass from the cutting-off position to the engaging position or from the engaging position to the cutting-off position; - a compact member comprising a magnetic triggering member and a triggering relay, said magnetic triggering member being formed by a magnetic triggering coil disposed around a movable core actuating a striker acting in case of short-circuit on the actuation mechanism and forming a portion of the first current conveying circuit, said triggering relay being formed by a triggering relay coil disposed around said movable core, the magnetic triggering coil and the triggering relay coil being disposed one around the other; - an electronic circuit connected to the triggering relay coil, said electronic circuit being configured to supply said triggering relay coil when predetermined current conveying conditions occur representing a prolonged overcurrent; characterized in that said electronic circuit (43a; 43d) comprises a prolonged overcurrent detector configured to determine the presence of said current conveying conditions from the signal present at the ends (110, 110a) of said triggering relay coil and to produce a detection signal when said predetermined current conveying conditions are present; and comprises a switching circuit with said prolonged overcurrent detector and said switching circuit being configured such that in the absence of said detection signal the switching circuit connects the triggering relay coil to the prolonged overcurrent detector whereas it isolates the triggering relay coil from each of said in connection terminals (22, 23), and such that in the presence of said detection signal the switching circuit isolates the triggering relay coil from the prolonged overcurrent detector then connects the triggering relay coil to each of said in connection terminals (22, 23). - a first current conveying circuit between the first in connection terminal and the out connection terminal, comprising a fixed contact and a movable contact; - an actuation mechanism of the movable contact having two stable positions, respectively a cutting-off position in which the movable contact is away from the fixed contact and an engaging position in which the movable contact bears on the fixed contact; - a lever to act manually on the actuation mechanism in order to pass from the cutting-off position to the engaging position or from the engaging position to the cutting-off position; - a compact member comprising a magnetic triggering member and a triggering relay, said magnetic triggering member being formed by a magnetic triggering coil disposed around a movable core actuating a striker acting in case of short-circuit on the actuation mechanism and forming a portion of the first current conveying circuit, said triggering relay being formed by a triggering relay coil disposed around said movable core, the magnetic triggering coil and the triggering relay coil being disposed one around the other; - an electronic circuit connected to the triggering relay coil, said electronic circuit being configured to supply said triggering relay coil when predetermined current conveying conditions occur representing a prolonged overcurrent;