The invention relates to a circuit element (10, 10') for data communication via at least one supply line (12), comprising at least one communication interface (20) for connecting to the at least one supply line (12), at least one supply interface (30), which is connected to the at least one communication interface (20) by means of a coupling coil (22), and at least one data interface (40) connected to a secondary communication unit (50). The communication interface (20) is connected to a primary communication unit (60) by means of a coupling capacitor (24), and the communication units (50, 60)can be coupled by means of a coupling unit (70).