The Siemens 5SU9404-1KK40 is a SENTRON 5SU9-series RCBO — an RCD-operated circuit breaker combining overcurrent and residual current protection in a single 18 mm module. Rated 40 A with a C tripping characteristic and 10 kA breaking capacity per EN 60898 and IEC 60947-2, it protects final circuits against overload, short-circuit, and AC earth faults in a 1P+N configuration.
Current derating and ambient limits
Above that, derate linearly: 37.6 A at 40 °C, 36.4 A at 45 °C, 34.8 A at 50 °C, 32.4 A at 55 °C. For a panel running warm — say 45 °C internal ambient — the usable continuous current drops to 36.4 A, so size the upstream protection accordingly.
Snaps onto DIN rail, any mounting position. 18 mm wide (1 width unit), 77 mm deep, 125 mm tall; installation depth is 70 mm. IP20 with the distribution board installed and conductors connected.
Listed as current production — no obsolescence notice on record.