The Siemens 5SU9304-6PK50 is a SENTRON RCBO — a combined residual-current device and miniature circuit breaker in one 18 mm wide module. It protects a single-phase final subcircuit against overload, short-circuit, and earth leakage in one package, saving a DIN rail position compared to separate RCD and MCB. Rated 40 A at 30 °C with B-curve tripping characteristic. 30 mA Type A residual current element catches sinusoidal AC and pulsating DC faults. Breaking capacity is 10 kA per both EN 60898 and IEC 60947-2, meaning it can safely interrupt fault currents up to that level at 230 V AC without welding contacts or cascading upstream. That covers most commercial and light industrial distribution boards; for higher fault levels you'd step to a higher-rated upstream device.
Mounting and integration
Snaps onto standard 35 mm DIN rail, occupies one modular width (18 mm). Depth is 77 mm, installation depth 70 mm — check gland-plate clearance if the enclosure is shallow. Mounting position is unrestricted, and the supply can enter from top or bottom, which simplifies busbar routing in a crowded panel. Degree of pollution 2, overvoltage category III — rated for fixed-installation distribution boards where transient overvoltages are controlled by upstream SPDs. IP20 with the distribution board installed and conductors connected; not for wet or washdown environments.