The online, double-conversion UPS 1b together with the fault arc detection devices 15a, 15b, the current detectors 16a, 16b and the light detectors 17a . . . 17f may be seen and denoted as a “combined power supply and arc quenching device”. Moreover, the short-circuiting switches 12a, 12b and/or the circuit breakers 13a . . . 13h may be part of such a combined power supply and arc quenching device, too.

The function of the electrical appliance 9b shown in FIG. 2 is as follows:

Again, the appliance sections 11a, 11b with their electrical consumers are powered by the online, double-conversion UPS 1a via its rectifier 3 and its inverter 4 in normal operation, that means that the bypass switch 6 is open in this state. During normal operation, also the circuit breakers 13a . . . 13h are closed (unless they are intentionally and manually opened to switch off certain sections 11a, 11b of the electrical appliance 9b). By means of the battery 8, fluctuations such as voltage spikes and sags occurring in the power grid 10 are compensated so that the electrical consumers are powered by a constant voltage.