What it is and what it does
The Siemens 5SU9356-1CN20 is a 1P+N RCD-operated circuit breaker (RCBO) from the SENTRON family, combining overcurrent protection and residual current protection in a single 2-module-width (36 mm) package. Rated 20 A with a C tripping characteristic, it handles moderate inrush loads like small motors and lighting banks without nuisance trips, while the integrated 30 mA Type AC residual current device protects against sinusoidal AC earth faults. Breaking capacity is 6 kA per both EN 60898 and IEC 60947-2, sufficient for most residential and light commercial distribution boards where the prospective fault current stays under that threshold.
What the ratings mean for fit
The C-curve (tripping between 5× and 10× In) means this RCBO is sized for circuits with a modest starting surge — think lighting groups, general-purpose sockets, or small fan/pump loads. For purely resistive loads or long cable runs where inrush is minimal, a B-curve would trip faster; for heavy motor starts, a D-curve would be needed. This part splits the difference. Temperature derating is published: 20 A at 30 °C, 18.6 A at 40 °C, 17.6 A at 45 °C, 17.2 A at 50 °C, and 16.6 A at 55 °C. If the panel ambient runs hot, factor the 40 °C or 50 °C figure into the load calculation — the 20 A label is only valid at 30 °C. Width is 36 mm (2 modular units), depth 77 mm, installation depth 70 mm. It mounts on standard DIN rail in any orientation and can be fed from top or bottom. The IP20 rating applies when installed in a distribution board with connected conductors — it's not a standalone outdoor device.