The Siemens 5SU1356-0KK20 is a SENTRON RCBO (residual current circuit breaker with overcurrent protection) combining a 2-pole 20 A MCB with Type B tripping characteristic and a 30 mA residual current device in a single 2-module-width (36 mm) housing.
Rated 20 A at 30 °C ambient; derates to 18.8 A at 40 °C, 17.4 A at 45 °C, 16.2 A at 55 °C, and 14.6 A at 70 °C. In a crowded enclosure with multiple RCBOs side-by-side, use the 40 °C or 50 °C column for realistic continuous load — the 20 A label is only valid in a 30 °C environment with adequate ventilation.