A crowbar device has a first terminal and a second terminal, the terminals being connectible to a medium to high impedance AC voltage source including a trigger circuit configured to output a trigger signal responsive to exceeding a threshold voltage across at least one trigger element of the trigger circuit; a positive-side signaling circuit and a negative-side signaling circuit configured to output a positive or a negative clamping signal, respectively, according to a positive-voltage or a negative-voltage signal, respectively, input from the trigger circuit; and a positive-side overvoltage clamping circuit and a negative-side overvoltage clamping circuit configured to control their respective semiconductor element to be in a conducting state, when the clamping signal from the corresponding signaling circuit is present, and configured to control their semiconductor element to be in a non-conducting state, when the corresponding clamping signal has not been present for a predetermined time period.