The Siemens 5SM1344-6FD is an FI-Protector Type A, rated at 40 A with a 30 mA residual current sensitivity across four poles at 400 V. This is the variant with PSE/SSF marking, meaning it's built for selective (time-delayed) and short-time delayed tripping — useful when you need coordination downstream of a main RCD to avoid a full panel blackout on a single fault. The 55 mm width (4TE) slots directly into a standard DIN-rail distribution board. Type A detection covers AC sinusoidal faults plus pulsating DC faults up to 6 mA, which is the standard for most modern electronics and single-phase rectified loads.
Four TE (55 mm) on a DIN rail — snaps into any standard distribution board or enclosure. The 30 mA sensitivity means it's the go-to for personnel protection (direct contact) rather than just equipment protection (300 mA or 500 mA). Type A is the minimum for circuits with single-phase VFDs, switching power supplies, or LED drivers that generate pulsating DC leakage. If your load is pure resistive or three-phase motor only, a Type AC would also work, but Type A covers both so it's the safer default for mixed loads.