What this RCBO is and what it does
The Siemens 5SU1654-0KK20 is a SENTRON RCBO — a combined residual-current circuit breaker and overcurrent miniature circuit breaker in a single 2-module-width (36 mm) housing. It protects a 1P+N circuit at 230/240 V AC, 50 Hz, with a Type B tripping characteristic for overcurrent and Type AC for earth leakage. The rated current is 20 A at 30 °C, with a published thermal derating curve for elevated ambient temperatures. Breaking capacity is 10 kA per EN 60898 and 20 kA per IEC 60947-2, giving the buyer two SCCR figures depending on which standard governs the installation.
Thermal derating — what the ambient-temperature table means for panel loading
The 20 A rating holds only at 30 °C. At 40 °C the RCBO is rated 18.8 A; at 50 °C it drops to 17.4 A; at 60 °C it is 16.2 A; at 70 °C it is 14.6 A. If the distribution board runs warm — say 50 °C inside the enclosure — the circuit must be loaded to no more than 17.4 A continuous. This is the figure a panel builder uses for conductor sizing and load scheduling, not the 30 °C number.
Physical fit and mounting
The 5SU1654-0KK20 occupies 2 modular width units (36 mm) on a DIN rail, with a depth of 77 mm and an installation depth of 70 mm. Height is 90 mm. Supply can enter from either top or bottom — no mandatory orientation. The housing is IP20 once installed in a distribution board with conductors connected; pollution degree 2 and overvoltage category III are standard for residential and light commercial panels. Halogen-free and silicon-free construction means the RCBO won't outgas corrosive compounds in a sealed enclosure or near sensitive electronics.