Case a) Again, the short-circuiting switch 12b associated with the fault arc A is closed to quench the fault arc A. Then, one of the circuit breakers 13a, 13b or 13e cuts off the faulty section of the electrical appliance 9b as a consequence of the excessive current flowing over said circuit breakers 13a, 13b or 13e. By providing different current trigger levels for the circuit breakers 13a . . . 13h, cutting off can take place in a predetermined way. Alternatively, a particular circuit breaker 13e may be directly triggered by the fault arc detection device 15b as this is depicted in FIG. 2. In this example, circuit breaker 13e is tripped. In the same way, the short-circuiting switch 12b may be tripped by the fault arc detection device 15b directly.

Case b) If the maximum output current of the inverter 4 is lower than the minimum current for keeping the fault arc A burning, the fault arc A is quenched “automatically” without the intervention of the short-circuiting switch 12b and the circuit breakers 13a, 13b or 13e. In this case, the hazardous situation is simply cleared by the current limitation of the inverter 4. As a consequence, the electrical appliance 9b can move over to normal operation again almost immediately.

In any case, the destructive impact of a fault arc A is significantly reduced, and the risk for damaging the electrical appliance 9b and injury of personnel is significantly reduced compared to prior art electrical appliances 9a.