In this embodiment, the override input 14 is connected to an input of the control unit 7 so that the bypass switch 6 it is inhibited from being closed indirectly. In this way, the control unit 7 may take further considerations and close the bypass switch 6 despite an active override signal under certain circumstances. However, the override input 14 may alternatively be connected with the bypass switch 6 so that switching over to bypass mode is directly influenced. That means an active override signal keeps the bypass switch 6 open in any case.

Thus, in case of a fault arc event, the current fed to the fault arc A is limited by the maximum output current of the inverter 4. As said, the maximum inverter current typically is 2 . . . 3 times the nominal current and much lower than the maximum current available from the power grid 10. By keeping the online, double-conversion UPS 1b in normal mode, the current fed to the fault arc A is significantly lower than the current occurring in a prior art electrical appliance 1a. Two cases are imaginable: