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
Full 40 A rating holds at 30 °C ambient. 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. The upper operating limit is 45 °C; storage range is -40 to +75 °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.
Mounting and wiring constraints
Snaps onto DIN rail, any mounting position. 18 mm wide (1 width unit), 77 mm deep, 125 mm tall; installation depth is 70 mm. Terminals accept solid or stranded conductors from 0.75 mm² up to 35 mm² — covers most final-circuit cable sizes. Supply can enter from top or bottom. IP20 with the distribution board installed and conductors connected.
Lifecycle and sourcing
Listed as current production — no obsolescence notice on record. This is a standard catalog item in the SENTRON RCBO line. Sourced and quoted to order against an RFQ through independent distribution; availability and current pricing confirmed at quote time.