A crowbar device having a first terminal and a second terminal, the terminals (1, 2) being connectible to a medium to high impedance AC voltage source, the crowbar device comprising a trigger circuit connected between the first terminal and the second terminal and configured to output a trigger signal responsive to exceeding a threshold voltage across at least one trigger element of the trigger circuit, wherein the trigger circuit comprises a stack of serially-connected trigger elements (BT1, BT2,..., BTn), the trigger circuit being configured to output the trigger signal responsive to exceeding the threshold voltage across the stack of serially-connected trigger elements (BT1, BT2,..., BTn), and wherein the trigger signal is a positive-voltage signal for a positive polarity overvoltage and a negative-voltage signal for a negative polarity overvoltage; a positive-side signaling circuit configured to output a positive clamping signal according to a positive-voltage signal input from the trigger circuit; a positive-side overvoltage clamping circuit comprising a controllable semiconductor element connected between the first terminal and the second terminal, the positive-side overvoltage clamping circuit being configured to control the semiconductor element to be in a conducting state when the positive clamping signal from the positive-side signaling circuit is present, and configured to control the semiconductor element to be in a non-conducting state when the positive clamping signal has not been present for a predetermined time period; a negative-side signaling circuit configured to output a negative clamping signal according to a negative-voltage signal input from the trigger circuit; a negative-side overvoltage clamping circuit comprising a controllable semiconductor element connected between the first terminal and the second terminal, the negative-side overvoltage clamping circuit being configured to control the semiconductor element to be in a conducting state when the negative clamping signal from the negative-side signaling circuit is present, and configured to control the semiconductor element to be in a non-conducting state when the negative clamping signal has not been present for a predetermined time period; characterized in that the predetermined time period is determined by a time constant at least partially defined by a diode connected, in the reverse direction, between an interconnection within the stack of serially-connected trigger elements (BT1, BT2,..., BTn) and an element of the positive-side overvoltage clamping circuit and/or a diode connected, in the reverse direction, between an interconnection within the stack of serially-connected trigger elements (BT1, Bt2,.. BTn) and the negative-side overvoltage clamping circuit. a trigger circuit connected between the first terminal and the second terminal and configured to output a trigger signal responsive to exceeding a threshold voltage across at least one trigger element of the trigger circuit, wherein the trigger circuit comprises a stack of serially-connected trigger elements (BT1, BT2,..., BTn), the trigger circuit being configured to output the trigger signal responsive to exceeding the threshold voltage across the stack of serially-connected trigger elements (BT1, BT2,..., BTn), and wherein the trigger signal is a positive-voltage signal for a positive polarity overvoltage and a negative-voltage signal for a negative polarity overvoltage; a positive-side signaling circuit configured to output a positive clamping signal according to a positive-voltage signal input from the trigger circuit; a positive-side overvoltage clamping circuit comprising a controllable semiconductor element connected between the first terminal and the second terminal, the positive-side overvoltage clamping circuit being configured to control the semiconductor element to be in a conducting state when the positive clamping signal from the positive-side signaling circuit is present, and configured to control the semiconductor element to be in a non-conducting state when the positive clamping signal has not been present for a predetermined time period; a negative-side signaling circuit configured to output a negative clamping signal according to a negative-voltage signal input from the trigger circuit; a negative-side overvoltage clamping circuit comprising a controllable semiconductor element connected between the first terminal and the second terminal, the negative-side overvoltage clamping circuit being configured to control the semiconductor element to be in a conducting state when the negative clamping signal from the negative-side signaling circuit is present, and configured to control the semiconductor element to be in a non-conducting state when the negative clamping signal has not been present for a predetermined time period; characterized in that the predetermined time period is determined by a time constant at least partially defined by a diode connected, in the reverse direction, between an interconnection within the stack of serially-connected trigger elements (BT1, BT2,..., BTn) and an element of the positive-side overvoltage clamping circuit and/or a diode connected, in the reverse direction, between an interconnection within the stack of serially-connected trigger elements (BT1, Bt2,.. BTn) and the negative-side overvoltage clamping circuit.