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.
What the ratings mean for fit
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. The C-curve (magnetic trip between 5× and 10× In) is the standard choice for motor-starting and transformer inrush in commercial and light industrial distribution boards. The 6 kA breaking capacity (per both EN 60898 and IEC 60947-2) tells you it safely interrupts a fault up to that prospective short-circuit current at the installation point. Overvoltage category III and pollution degree 2 mean it is rated for fixed-installation distribution boards, not for outdoor or heavily contaminated environments. The IP20 rating applies when the distribution board is installed with connected conductors — the breaker itself is not sealed against dust ingress.
Integration and mounting
Two modular-width units (36 mm wide, 77 mm deep, 90 mm high) snap onto a DIN rail. Installation depth is 70 mm behind the panel face. The supply can enter from either top or bottom, and the breaker can be mounted in any position — no orientation restrictions. 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.