Apparatus for powering a customer network with the electric power of a supply network

A device (1) for supplying a customer network (13) with electric power of a supply network (12), said apparatus (1) a frequency converter (2) has, on the one hand to the supply network (12) and the other (with the customer network 13 ) connectable to provide, with which even high short-circuit currents can be provided for a sufficiently long period of time for the customer network, so that a short circuit can be located in the customer network and selectively separated from the remaining fault-free pickup network can be a mechanical switch unit (3), parallel to the frequency converter (2) and to bridge of the frequency converter (2) is arranged, and suggested connected by the switching unit (3) control means (9), the current flowing in detecting a by the frequency converter (2) short-circuit current for actuating the switching unit (2) are arranged.