A method for operating an electrical power supply network is described. The power supply network has several levels of different voltages. The levels are interconnected by switches. A first switch is made so that the maximum interruptible short-circuit current of the first switch is smaller than the maximum flowing short-circuit current. In the event of failure, a test is made as to whether the short-circuit current presently flowing through the first switch is smaller than the maximum interruptible short-circuit current. The first switch will remain closed if this is not the case, and the first switch will be opened if this is the case.