The protection concept to be created should be cheaper, without compromising quality of supply. It is justifiable to consider implementing a concept which, although it might slightly increase unavailability, allows in the medium and longer term large financial savings to be made. A further advantage of the proposed concept is that a whole circuit would not have to be re-equipped all at the same time. Through an analysis of the medium voltage network of the city of Zurich unavailability with the existing protection technology could be determined. This investigation revealed that only 20% of unavailability is actually due to the medium voltage protection technology. In view of the proposed market liberalisation it is desirable for all customers in the network to enjoy the same quality of supply. To achieve the goal the circuit-breakers in the system would be replaced by disconnecting switches which are less expensive to purchase and maintain. Moreover, the system would be operated open. Only directly at the bus, the half-circuits would be secured by circuit-breakers. By this measure, in the event of a short-circuit the whole half circuit would be separated by the circuit-breaker from the supply network. The interruption duration could be significantly reduced by means of more effective signalling. By arrangement with the partner company EWZ resolved to examine in detail signalling via SMS using the GSM network. This method would be simple to implement and would have the advantage that the location of the short-circuit could be communicated rapidly and reliably to the center of operations, from where this information could then be forwarded to the service team on duty. The time required to reconnect consumers to their supply could by this procedure be reduced from the 90 minutes it takes today to about 70 minutes, so that unavailability, which is made up of both how long and how frequently there are interruptions to supply would remain practically unchanged.