The Siemens 5SM3344-6KL is a SENTRON 5SM3-series residual current operated circuit breaker (RCCB), 4-pole, type A, rated 40 A at 400 V AC with a 30 mA trip threshold — the standard sensitivity for personnel protection in most IEC-based distribution boards. It is an instantaneous (short-time delayed: No) design, meaning it trips without intentional delay on a fault, so it sits on the load side of a selective main switch.
Mounts on DIN rail (REG profile) in any position — no derating for upside-down or sideways installs. It occupies 4 width units (72 mm) on the rail, with a depth of 77 mm and an installation depth of 70 mm, so it fits standard 18 mm pitch enclosures. The N pole is on the left side of the device (product variation: N left). Screw terminals accept solid or stranded conductors from 1.5 to 25 mm²; tighten to 2.5–3 N·m.