RCBO for 50 Hz distribution boards
The Siemens 5SU1354-0KK40 is a 2-pole residual current operated circuit breaker (RCBO) from the SENTRON series, combining overcurrent protection and residual current detection in a single 36 mm wide (2 modular width units) package for 50 Hz systems. Rated at 40 A with a B tripping characteristic. Energy limitation class 3. The residual current element is type AC, meaning it detects sinusoidal AC fault currents only — suited for circuits without rectified or pulsed DC loads.
Breaking capacity and selectivity
Short-circuit breaking capacity is rated at 10 kA per EN 60898 and 15 kA per IEC 60947-2. The higher IEC figure applies when the device is used as an industrial molded-case equivalent; the EN figure governs residential and commercial distribution board coordination. Energy limitation class 3 means the let-through energy is low enough to protect downstream wiring and loads under fault conditions — relevant for selectivity studies with upstream SENTRON NH fuse-links or SENTRON 3VA breakers.
Thermal derating and installation constraints
Full 40 A rating holds at 30 °C ambient. Derate to 37.6 A at 40 °C, 36.4 A at 45 °C, 34.8 A at 50 °C, 32.4 A at 55 °C and 60 °C, 30.8 A at 65 °C, and 29.2 A at 70 °C. Panel builders must apply these values when grouping multiple RCBOs in a confined enclosure. Mounting position is unrestricted, and the supply can enter from either top or bottom — simplifies busbar routing in a crowded distribution board. Installation depth is 70 mm, overall depth 77 mm. Degree of pollution 2 and overvoltage category III suit fixed-installation distribution boards. IP20 applies once the board is closed with conductors connected.