A supply voltage monitoring device (100; 600) for monitoring over voltage conditions of an AC power supply, comprising: a switch circuit configured to couple an input conductor connectable to the AC power supply to an output conductor connectable to a load, the switch circuit being switchable into a conductive state, where the input conductor is electrically connected to the output conductor through the switch circuit and switchable into a non-conductive state, where the input conductor is electrically disconnected from the output conductor by the switch circuit; a supply signal conditioning circuit configured to generate a supply voltage signal representative of a voltage of the AC power supply,; and a control circuit configured to monitor the supply voltage signal for over voltage conditions, the control circuit being configured to: control the switch circuit into the conductive state in response to the supply voltage signal being below a first over voltage threshold while the switch circuit is in the non-conductive state; and control the switch circuit into the non-conductive state in response to the supply voltage signal exceeding a third over voltage threshold that is higher than a second over voltage threshold that is higher than the first over voltage threshold while the switch circuit is in the conductive state, characterized in that the control circuit is further configured to record an indication of an occurrence of an over voltage event and control the switch circuit to remain in the conductive state in response to the supply voltage signal exceeding the second over voltage threshold while the switch circuit is in the conductive state. a switch circuit configured to couple an input conductor connectable to the AC power supply to an output conductor connectable to a load, the switch circuit being switchable into a conductive state, where the input conductor is electrically connected to the output conductor through the switch circuit and switchable into a non-conductive state, where the input conductor is electrically disconnected from the output conductor by the switch circuit; a supply signal conditioning circuit configured to generate a supply voltage signal representative of a voltage of the AC power supply,; and a control circuit configured to monitor the supply voltage signal for over voltage conditions, the control circuit being configured to: control the switch circuit into the conductive state in response to the supply voltage signal being below a first over voltage threshold while the switch circuit is in the non-conductive state; and control the switch circuit into the non-conductive state in response to the supply voltage signal exceeding a third over voltage threshold that is higher than a second over voltage threshold that is higher than the first over voltage threshold while the switch circuit is in the conductive state, control the switch circuit into the conductive state in response to the supply voltage signal being below a first over voltage threshold while the switch circuit is in the non-conductive state; and control the switch circuit into the non-conductive state in response to the supply voltage signal exceeding a third over voltage threshold that is higher than a second over voltage threshold that is higher than the first over voltage threshold while the switch circuit is in the conductive state, characterized in that the control circuit is further configured to record an indication of an occurrence of an over voltage event and control the switch circuit to remain in the conductive state in response to the supply voltage signal exceeding the second over voltage threshold while the switch circuit is in the conductive state.