Method for operating an electric installation system comprising a main station and a connected substation

The method involves executing control commands on an electrical conductor (2) in a voltage-coded manner in a negative half-wave for controlling a main station (HS) by a substation (NS), where the main station is connected to the substation over the conductor. A feedback half-wave is used for transmission of data from the main station to the substation when information to be transmitted to the substation is provided based on the feedback half-wave. An optical signal is provided by an LED (3) for indicating switching status information of the substation.