What this RCBO is and what the ratings mean for fit
The Siemens 5SU9354-8KK16 is a SENTRON RCBO — an RCD-operated circuit breaker combining overcurrent and residual-current protection in a single 2-module-wide (36 mm) package. It's a 1P+N design, meaning it switches and protects the line conductor only; the neutral is switched but not protected. That's standard for single-phase final circuits in TN or TT systems where you don't need a protected neutral. The D tripping characteristic means the magnetic release trips at 10 to 20 times the rated current. That's deliberately high — D-curve is for loads with a large inrush, like small motors, transformers, or discharge lighting. If you're protecting a resistive or general-purpose circuit, a B or C curve would nuisance-trip less; D is the right call for inductive or high-starting-current loads. Rated 16 A at 30 °C ambient, but the thermal derating curve is published: 15.04 A at 40 °C, 14.56 A at 45 °C, 13.92 A at 50 °C, and 12.96 A at 55 °C (–). If your panel ambient runs at 45 °C, you're effectively working with a 14.56 A device — plan your load accordingly. The breaking capacity is 10 kA per both EN 60898 and IEC 60947-2, which covers most residential and light commercial service-entrance fault levels. Overvoltage category III and pollution degree 2 confirm it's rated for fixed-installation downstream of the main distribution board.
Panel integration and mounting
Snap-on mounting to DIN rail (implied by the SENTRON modular form factor). At 2 MWU (36 mm wide,) it occupies two standard 18 mm slots. Installation depth is 70 mm; total depth including the front projection is 77 mm. That's a shallow profile — fits most distribution boards without crowding the gland plate. Supply can enter from top or bottom, which simplifies busbar routing. IP20 rating applies only when the distribution board is installed and conductors are connected — not a washdown device, keep it inside a closed panel.