As soon as the AC voltage supply moves outside the safe operating window (190 Volts Low to 265 Volts High/230V AC 50Hz) PowerGuard Extreme Notebook Protector immediately switches OFF power to the protected equipment and remains OFF until a safe mains supply voltage is detected, giving sensitive equipment proper protection when needed and whenever isolation occurs, providing the connected equipment with a vital minimum time delay before power is restored (e.g. prevents hard drive lock-up in computer equipment).The PowerGuard Extreme Notebook Protector is not earth dependent or amperage reacting, therefore events such as loss of a neutral link and the resultant continuous high voltage is rapidly detected and protection is activated, before damaging your vital electrical or electronic equipment. Reliable protection 24/7.