What it is and what it does
The Siemens SENTRON 5SU1354-6LB25 is a combined residual current circuit breaker with overcurrent protection (RCBO) — a single device that does the job of an MCB and an RCD in one 2-module-width (36 mm) package. Rated 25 A at 30 °C with a B-curve trip characteristic, it protects final circuits against overload and short-circuit while also detecting earth leakage currents. The residual current element is Type A, meaning it responds to sinusoidal AC fault currents and pulsed DC fault currents up to 6 mA — the standard for circuits with single-phase rectifiers, switched-mode power supplies, or electronic loads. Breaking capacity is 10 kA per EN 60898 and 20 kA per IEC 60947-2, giving headroom for high-fault installations.
What those ratings mean for your panel
The 25 A rating at 30 °C is the headline figure, but the derating table tells the real story: at 40 °C the continuous current drops to 23.5 A, at 50 °C to 21.75 A, and at 70 °C to 18.25 A. If this RCBO sits in a crowded distribution board where ambient can reach 50 °C, plan for a 21.75 A continuous load — not 25 A. The short-time delayed K characteristic means it tolerates brief inrush without nuisance tripping, useful for motor-starter or capacitive-load circuits. Mounting position is unrestricted, and the supply can enter from top or bottom — no orientation restrictions in the cabinet.
Compliance and documentation
The device is halogen-free and silicon-free, which matters for clean-room or high-reliability installations where outgassing can contaminate contacts or optics. Protection class is IP20 once installed in a distribution board with connected conductors — standard for enclosed panel-mount gear. Overvoltage category III and pollution degree 2 confirm suitability for fixed-installation mains circuits within a building's distribution network.