Since the arc energy grows as the square of the current, limiting the arc current with the UPS inverter reduces the arc energy to a fraction of the arc energy appearing otherwise.

This reduces the risk for personnel and installation and limits the damage to equipment caused by the fault arc. Furthermore, long downtimes due to excessive damage to the electrical appliance is avoided.

In detail, the fault arc detection device monitors the electrical appliance downstream of the UPS. Once the fault arc detection device detects a fault arc, it outputs a fast signal to the UPS to prevent it from transferring to bypass mode and to keep feeding the fault arc with the inverter of the UPS thus limiting the arc current. Optionally, the UPS annunciates an alarm related to the fault arc detection signal.

The fault arc detection device can also output a trip signal to a circuit breaker feeding the faulty area of the electrical appliance to quickly isolate the faulty circuit. The quick disconnection of the fault arc reduces the arc energy even more and minimizes the impact of the fault to other parallel circuits fed by same UPS. A typical arc clearing time using a fault arc detection device is approximately 30-50 ms including both the detection time and circuit breaker operation time. Within this time, excessive air pressure caused by the fault arc can already cause significant damage to equipment and hurt of human beings. Limiting the arc current before the fault arc is cleared by means of a circuit breaker, substantially decreases air pressure and heat impact of a fault arc in view of prior art systems.