The Siemens 5SU9104-1KK20 is a SENTRON RCBO — an RCD-operated circuit breaker that combines overcurrent and residual-current protection in a single 1 MW (18 mm) wide module. It's a 1P+N design, meaning it switches the live pole and monitors the neutral, with a C-curve trip characteristic rated at 20 A at 30 °C and a 10 kA breaking capacity per both EN 60898 and IEC 60947-2.
At 18 mm wide and 77 mm deep, it occupies one modular unit.
Temperature derating and environmental limits
Above that, derate: 18.8 A at 40 °C, 18.2 A at 45 °C, 17.4 A at 50 °C, and 16.2 A at 55 °C. Max 95% humidity, pollution degree 2, overvoltage category III — standard for fixed-installation residential or light commercial sub-distribution.