The Siemens 5SU9354-7KK40 is a SENTRON RCD-operated circuit breaker — an RCBO that combines overcurrent protection and residual-current detection in a single 2-module-wide (36 mm) package. Rated 40 A at 30 °C ambient, it derates to 37.6 A at 40 °C and 32.4 A at 55 °C — the thermal curve matters when the panel runs hot. The IP20 rating applies once installed in a distribution board with connected conductors — not for open-panel or wet-area use.
The 1P+N design protects the phase conductor only; the neutral is switched but not protected — standard for single-phase RCBOs in TN or TT systems. The 2 MW width (36 mm) occupies two 18 mm DIN spaces, so factor that into your enclosure fill count. The 4 kV surge voltage resistance covers typical mains transients. The 1 kA surge current withstand (8/20 µs) handles lightning-induced spikes on the line side.