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. It is designed for DIN-rail mounting in distribution boards, protecting final circuits against both overload/short-circuit and earth fault currents. Breaking capacity is rated at 6 kA per EN 60898 and 15 kA per IEC 60947-2 — the higher IEC figure gives headroom for industrial panels where fault levels exceed domestic limits, while the EN rating covers standard residential/commercial installations. The Type B characteristic trips instantaneously at 3 to 5 times rated current, making it suitable for resistive and general-purpose loads with low inrush — typical for lighting, socket outlets, and small motor circuits where the inrush stays under that multiple.
Thermal derating and mounting
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. Mounting position is unrestricted, and the 70 mm installation depth fits standard shallow enclosures. The IP20 rating applies when installed in a distribution board with conductors connected — not rated for wet or dust-exposed locations without an outer enclosure.