To reduce the destructive impact of a fault arc A, a modified online, double-conversion uninterruptible power supply 1b is proposed, which again comprises a UPS input 2, a rectifier 3, which with its input is connected to the UPS input 2, an inverter 4, which with its input is connected to an output of the rectifier 3, a UPS output 5 being connected to the output of the inverter 4, a bypass switch 6 being between the UPS input 2 and the UPS output 5 and a control unit 7 for closing the bypass switch 6 in case of excessive output current and/or excessive voltage drop and/or excessive power demand at the UPS output 5. In addition, the proposed online, double-conversion UPS 1b comprises an override input 14, which when activated inhibits closing the bypass switch 6. Such an online, double-conversion UPS 1b is shown in FIG. 2.

Furthermore, the electrical appliance 9b shown in FIG. 2, which is similar to the electrical appliance 9a shown in FIG. 1, in addition, comprises fault arc detection devices 15a, 15b, which in this embodiment are connected to current detectors 16a, 16b and light detectors 17a . . . 17f Alternatively, embodiments are imaginable in which the fault arc detection devices 15a, 15b are just connected to current detectors 16a, 16b or just connected to light detectors 17a . . . 17f.