What it is and what it does
The Siemens SENTRON 5SU1354-0KK20 is a 2-pole RCBO — a combined residual-current device and miniature circuit breaker in one 36 mm wide (2 MW) package. It protects a single-phase 230/240 V AC circuit at 50 Hz, with a B-curve overcurrent trip for lighting or general-purpose loads and a Type AC residual-current trip for sinusoidal AC faults. The unit is rated 20 A at 30 °C and carries a 10 kA breaking capacity per EN 60898 (20 kA per IEC 60947-2), so it handles typical domestic or light commercial fault levels without upstream coordination worries.
Fit and derating
At 36 mm wide and 77 mm deep (70 mm installation depth), this RCBO drops into a standard DIN-rail distribution board with IP20 protection once installed and conductors connected. It accepts supply from either top or bottom and can be mounted in any position. The temperature derating is published: 20 A at 30 °C, 18.8 A at 40 °C, 16.2 A at 55 °C, down to 14.6 A at 70 °C — so if your panel runs hot, size the circuit accordingly. Overvoltage category III and pollution degree 2 mean it's rated for fixed-installation mains-level transients, not just downstream electronics.