What this RCBO carries
The Siemens SENTRON 5SU1354-1KK20 is a 1P+N RCBO (residual current circuit breaker with overcurrent protection) rated 20 A at 30 °C with a C tripping curve — the standard choice for motor and lighting circuits where inrush won't nuisance-trip a B-curve. It breaks 10 kA per EN 60898 and 20 kA per IEC 60947-2, so it handles residential and light commercial fault levels without cascading upstream.
Fit and integration
Two modular-width units (36 mm) snap onto standard DIN rail. Depth is 77 mm, installation depth 70 mm — check your enclosure's gland-plate clearance; some shallow consumer units need the 70 mm figure. Mount in any position, feed from top or bottom. IP20 only with conductors connected and the distribution board installed, so it's strictly indoor panel use.
Thermal derating — the real current
The 20 A rating holds at 30 °C ambient. At 40 °C it's 18.8 A; at 50 °C it's 17.4 A; at 60 °C it's 16.2 A; at 70 °C it's 14.6 A. If your panel runs hot — say, a packed enclosure near a drive — size the load to the derated figure, not the label.