The Siemens 5SU1356-6KK20 is a SENTRON RCBO (residual current circuit breaker with overcurrent protection) rated 20 A at 30 °C, with a 30 mA Type A residual current trip and B-curve overcurrent characteristic. It breaks fault currents up to 6 kA per EN 60898, which covers the standard domestic and light commercial fault level requirement. The 2-pole unit occupies 2 modular width units (36 mm) on a DIN rail.
Temperature derating matters for panel fill
The 20 A rating holds at 30 °C ambient. At 40 °C it derates to 18.8 A, at 50 °C to 17.4 A, and at 70 °C to 14.6 A. If this RCBO sits in a crowded enclosure with other heat sources, the actual continuous current it can carry drops — size the circuit load against the derated value, not the 30 °C number. Mounting position is any, so vertical or horizontal DIN-rail orientation won't change the thermal performance.
The RCBO is halogen-free and silicon-free, which matters for installations with sensitive electronics or where outgassing during a fault could corrode contacts. Touch protection is built in. The supply cord can enter from top or bottom, giving flexibility in panel layout. IP20 rating applies when installed in a distribution board with connected conductors — it's not a standalone outdoor device.