To improve functional security in electric power systems, a fault detector is provided in the electric power system that is connected to the data communication bus and that evaluates streamed values of at least one process parameter. In order to detect an electric fault in the electric power system, the fault detector is arranged to send a fault present indication to the switching element when an electric fault is detected. The fault present indication is sent to and received by the switching element, before the tripping operation of the switching element is triggered upon receipt of the switching command from the automation system, and the switching element triggers the tripping operation of the switching element only when a fault present indication has been received.