Low-voltage circuit breaker having: - at least one current sensor (SE1, SE2, SE3, SEN), for determining the level of the electrical current through a conductor (L1, L2, L3, N), associated with the current sensor, of the low-voltage circuit breaker, - at least one electromechanical switching unit for connecting and disconnecting at least two electrical contact points (KSB, KSF), of which at least one is movable in such a way that, in a first switching position of the movable contact point, the contact points (KSB, KSF) are connected to one another and, in a second switching position, the contact points (KSB, KSF) are not connected to one another, - at least one electronic switching unit, which has a semiconductor switching element, is electrically conductive in a first switching state and electrically blocking in a second switching state, and is connected electrically in parallel with the electromechanical switching unit, - an electronic trip unit, which is connected to the current sensor (SE1, SE2, SE3, SEN), the electronic switching unit and the electromechanical switching unit, and is configured in such a way that, when current or/and current/time span limit values of the conductor are exceeded, first disconnection of the electromechanical switching unit and then blocking of the electronic switching unit takes place, wherein the electromechanical switching unit is configured as a vacuum circuit breaker (EMVP), in which the contact points (KSB, KSF) are in the vacuum, wherein at least one electromechanical disconnecting unit is provided, which is arranged electrically in series with the parallel circuit comprising the vacuum circuit breaker (EMVP) and the electronic switching unit, wherein the electromechanical disconnecting unit is connected to the electronic trip unit and, when current or/and current/time span limit values of the conductor are exceeded, first disconnection of the vacuum circuit breaker (EMVP) and then blocking of the electronic switching unit takes place, and subsequently disconnection of the electromechanical disconnecting unit takes place, characterized in that the semiconductor switching element is an IGBT, and in that a piezoelectric actuator is provided for the change in switching position of the electromechanical switching unit. - at least one current sensor (SE1, SE2, SE3, SEN), for determining the level of the electrical current through a conductor (L1, L2, L3, N), associated with the current sensor, of the low-voltage circuit breaker, - at least one electromechanical switching unit for connecting and disconnecting at least two electrical contact points (KSB, KSF), of which at least one is movable in such a way that, in a first switching position of the movable contact point, the contact points (KSB, KSF) are connected to one another and, in a second switching position, the contact points (KSB, KSF) are not connected to one another, - at least one electronic switching unit, which has a semiconductor switching element, is electrically conductive in a first switching state and electrically blocking in a second switching state, and is connected electrically in parallel with the electromechanical switching unit, - an electronic trip unit, which is connected to the current sensor (SE1, SE2, SE3, SEN), the electronic switching unit and the electromechanical switching unit, and is configured in such a way that, when current or/and current/time span limit values of the conductor are exceeded, first disconnection of the electromechanical switching unit and then blocking of the electronic switching unit takes place, wherein the electromechanical switching unit is configured as a vacuum circuit breaker (EMVP), in which the contact points (KSB, KSF) are in the vacuum, wherein at least one electromechanical disconnecting unit is provided, which is arranged electrically in series with the parallel circuit comprising the vacuum circuit breaker (EMVP) and the electronic switching unit, wherein the electromechanical disconnecting unit is connected to the electronic trip unit and, when current or/and current/time span limit values of the conductor are exceeded, first disconnection of the vacuum circuit breaker (EMVP) and then blocking of the electronic switching unit takes place, and subsequently disconnection of the electromechanical disconnecting unit takes place, characterized in that the semiconductor switching element is an IGBT, and in that a piezoelectric actuator is provided for the change in switching position of the electromechanical switching unit.