The diagnosis and protection module enables quick diagnostics of the bus state and indicates telegram traffic via an LED. A bus failure (U<min) can be signalled via the changeover contact. The DSM incorporates a suppressor diode (43V / 1500W @ 10/1000 μs pulse) which suppresses transient overvoltages and interference voltage spikes. It is recommended to apply the device as a “disconnection point”, for example between building sections, to provide optimum protection.