The Siemens SENTRON 5SU9304-6PK32 is an 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 (10 kA per EN 60898 and IEC 60947-2), and earth leakage (30 mA, Type A). The B-curve trips between 3 and 5 times rated current, so it's sized for resistive and general-purpose loads where inrush is modest — lighting, small heaters, control transformers, socket outlets in residential or light commercial panels. Rated 20 A at 30 °C on a 230/240 V AC supply, it occupies one modular width (18 mm) on a DIN rail. The 1P+N design switches the phase and switches the neutral solidly — no switched neutral contact to fail. A 1200 mm factory-attached pigtail on the neutral side speeds panel wiring, and the supply can enter from top or bottom, so you don't have to reorient the busbar arrangement.
What the ratings mean for fit
The 10 kA breaking capacity (both EN 60898 and IEC 60947-2) tells you this RCBO can safely interrupt a fault current up to 10,000 A at its rated voltage. That covers the prospective short-circuit current you'd typically find at the final distribution board in a residential or light commercial installation fed by a transformer of modest kVA. If your site's available fault current exceeds 10 kA, you'll need a current-limiting upstream device or a higher-rated breaker — this unit won't hold. The B-curve characteristic means the magnetic trip activates at 3–5× In (60–100 A for this 20 A unit). That's fast enough to protect cable and equipment against short circuits, but it won't nuisance-trip on the inrush of a few fluorescent fittings or a small motor starting direct-on-line. If you're feeding a circuit with high inrush — say a bank of LED drivers or a small compressor — a C-curve sibling would be the better call. Type A RCD detects sinusoidal AC residual currents plus pulsating DC residual currents (up to 6 mA smooth DC superimposed). That covers most modern electronics — switched-mode power supplies, variable-speed drives, LED drivers — that can generate pulsating DC leakage. If your load includes three-phase rectifiers or frequency inverters that might produce pure DC fault current, you'd need Type B.
Panel integration and environment
The 18 mm width (one modular unit) is the standard DIN-rail footprint for a 1P+N RCBO. It clips onto a 35 mm DIN rail and sits 77 mm deep plus 70 mm installation depth — the extra 7 mm accounts for the pigtail bend radius behind the unit. Height is 125 mm, so it clears most 150 mm-tall consumer unit enclosures. IP20 protection applies when the distribution board is installed with conductors connected — that's the standard for inside an enclosure. Not rated for wet or dusty environments. Operating temperature range is -40 °C to 75 °C, with up to 95% humidity, so it's fine for unheated utility rooms or outdoor-rated enclosures in temperate climates. Overvoltage category III and pollution degree 2 mean it's designed for fixed installation downstream of the main distribution board — typical for final subcircuits in buildings. The 4 kV surge voltage rating (impulse withstand) covers the transients you'd expect in a TN or TT system.