The as surge protection type 3 (formerly D-fine protection) Which can be used in a sub-distribution unit can protect the home next to Automatic application other 24 V and RS-485 systems. It is designed for mounting on DIN rail . In addition to the protection against transients, the device thus protects devices connected behind with the central 24 V power supply unit failure. Additionally, the protective function of a switchable RS485 bus termination is present, as did may account for additional bus termination resistors.