The Siemens SENTRON 5SM3444-0LA is a 4-pole residual current operated circuit breaker (RCCB) for AC fault currents, rated 40 A continuous and 100 mA residual trip threshold at 400 V AC line voltage. The 100 mA sensitivity is the deciding spec for fit: it protects against indirect contact (equipment ground-fault) rather than direct human contact — 30 mA is the standard for personal shock protection. The RCCB also includes thermal overload protection, so it doubles as a combined residual-current/overload device in a single 4-module-width package. The IP20 rating applies once the distribution board is installed with conductors connected; the enclosure provides the environmental seal.
The 5SM3444-0LA occupies 4 width units (roughly 72 mm) on the DIN rail. The silicon-free construction (marked) is relevant for applications where outgassing must be avoided, such as in sealed cabinets near sensitive electronics. The finger and back-of-hand safe design meets the touch-protection requirements of EN 50274 for the terminals.