The Siemens 5SU9356-1CN40 is a SENTRON RCD-operated circuit breaker — an RCBO that combines overcurrent protection and residual current detection in a single 2-module-wide (36 mm) package. Rated 40 A at 30 °C with a C-curve trip characteristic, it breaks fault currents up to 6 kA per EN 60898 and IEC 60947-2. The 1P+N design protects one phase while switching the neutral, and the instantaneous residual-current element responds without intentional delay.
The 40 A rating at 30 °C is the headline number, but the derating curve matters in a warm panel: at 40 °C it carries 37.2 A, at 45 °C 35.2 A, at 50 °C 34.4 A, and at 55 °C 33.2 A. If your enclosure runs above 30 °C, size the load against the derated figure, not the 40 A label.
Two modular-width units (36 mm wide, 77 mm deep, 90 mm high) snap onto a DIN rail. Halogen-free and silicon-free construction is specified, which matters for panels in environments sensitive to corrosive off-gassing, such as pulp and paper mills or food processing lines.