The Siemens 5SM3344-6KK12 is a SENTRON 5SM3-series residual current circuit breaker (RCCB) — a 4-pole, Type A device rated 40 A at 400 V AC. Type A means it detects sinusoidal AC fault currents plus pulsating DC fault currents up to 1 kHz, which covers most modern electronic loads (VFDs, switched-mode supplies, lighting ballasts) that a plain AC-sensitive RCCB would miss. The instantaneous design (no intentional time delay) trips as soon as the residual current exceeds the threshold, so it goes upstream of the load, not downstream of a selective main.
Above that, the curve steps down: 38.4 A at 50 °C, 36.8 A at 55 °C, 35.2 A at 60 °C, 33.6 A at 65 °C, and 32 A at 70 °C. Mounting is snap-on DIN rail (REG profile), any position. The 4-pole, 4-module width (72 mm) fits a standard 18 mm/module DIN rail footprint. IP20 with conductors connected and distribution board installed — standard for enclosed panels, not for open washdown areas.
The 4-module width (72 mm) occupies four 18 mm slots — plan your fill factor accordingly. Supply feeds from the bottom per the manufacturer's position marking. The finger- and back-of-hand-safe terminals (IPXXB/IP2X) meet the protection class for live-part access in a closed panel. Silicon-free construction matters if this goes into a paint shop or coating line where silicone outgassing would cause fisheyes.