What the 5SU1654-1KK20 is and what it does
The Siemens 5SU1654-1KK20 is a SENTRON RCBO — a combined residual-current circuit breaker with overcurrent protection — in a 1P+N, 2-pole housing that protects one live conductor and switches the neutral. Rated 20 A at 30 °C with a C tripping characteristic, it handles the inrush from motor starters and small transformers without nuisance trips, while the 30 mA residual-current element catches ground faults. The 10 kA breaking capacity per EN 60898 (20 kA per IEC 60947-2) means it can safely clear a bolted fault on a 230/240 V, 50 Hz supply without upstream damage. Overvoltage category III and pollution degree 2 suit it for fixed-installation distribution panels — the standard environment for a DIN-rail RCBO in commercial or light industrial switchgear.
Derating and real-world current capacity
The 20 A rating is at 30 °C ambient. At 40 °C it derates to 18.8 A, at 50 °C to 17.4 A, and at 70 °C to 14.6 A. If the panel runs hot — say near a transformer or in a non-ventilated enclosure — the continuous load must stay under the derated figure; otherwise the bimetal strip will heat-trip on a sustained current well below 20 A. The 2 MW width (36 mm) leaves room for adjacent breakers in a crowded DIN rail; mounting position is unrestricted, and the supply can enter from top or bottom, which simplifies busbar layout.