The Siemens 5SM3344-3 is a SENTRON 5SM3-series residual current circuit breaker (RCCB) — a 4-pole, 40 A, 30 mA Type F device with short-time delayed switching.
Type F detection handles AC sinusoidal residual currents plus pulsed DC (like from a VFD or washing machine rectifier) and high-frequency AC superimposed on smooth DC, which is common in modern inverter-fed equipment. The short-time delayed characteristic (selective) means it withstands transient leakage pulses up to 3 kA surge current without nuisance tripping, so it can be used downstream of a time-delayed main RCCB for selectivity. Rated current derates with ambient temperature: 40 A up to 45 °C, then 38.4 A at 50 °C, stepping down to 32 A at 70 °C. In a warm panel near the top of a cabinet, factor that derating into your load calculation — the 40 A rating is only valid below 45 °C ambient.
Snap-on DIN rail (REG) mount, 4 width units (72 mm at 18 mm/module). Installation depth is 70 mm. Finger and back-of-hand safe per the IP20 rating once the distribution board cover is installed.