The backbone/line coupler interconnects two KNX lines into a logical function area ensuring at the same the electrical separation between these lines. Each bus line of a KNX installation can thus be operated electrically independently from other bus lines. The exact function of the device is determined by the selected parameterization and by the physical address. The device can be used as an backbone coupler, line coupler or line repeater for implementing line segments in existing new KNX installations.