The Siemens SENTRON 5SM3444-8LA is a 4-pole residual current circuit breaker (RCCB) in the selective (time-delayed) design, Type A, rated 40 A at 400 V AC with a 100 mA trip threshold. The selective characteristic means it holds through short-duration earth faults and transient surges up to 5 kA surge current resistance, letting a downstream RCCB trip first — so only the faulted branch drops out, not the whole submain. That coordination matters in a distribution board feeding multiple circuits where you want the closest device to the fault to open, not the upstream main. Rated for 10 kA short-circuit current rating (SCCR) at 400 V AC, overvoltage category III, so it sits comfortably in a commercial or industrial sub-distribution board where fault levels are moderate. The 4-pole construction switches all lines including neutral, and the built-in thermal overload protection adds a second layer — it's not just a plain RCCB, it also protects against sustained overcurrent on the phase conductors.
Ambient limits and panel fit
The 45 °C ceiling is the running limit — if the panel ambient pushes above that, you need to derate or ventilate. Mounts on DIN rail (REG), any orientation, 4 width units (72 mm at 18 mm per unit), 70 mm installation depth. IP20 with connected conductors in an installed distribution board — standard for enclosed panels, not for wet locations. Finger and back-of-hand safe per the shock protection class, so live terminals are shielded when the front cover is on.