The Siemens 5SM1612-0FD is a 2-pole FI-Protector (residual current device) rated 25 A, Type AC, with a rated residual current IΔn of 0.3 A at 230 V. It occupies 2 TE (module spaces) on a DIN rail, 55 mm deep.
For circuits with rectifiers, VFDs, or switched-mode supplies, a Type A or Type B device would be required. The 0.3 A (300 mA) IΔn is a fire-protection threshold, not a personnel-protection level (which typically requires 30 mA or lower). This unit is sized for branch-circuit or feeder protection where the goal is to prevent cable overheating and fire, not direct shock protection. At 25 A rated current and 2-pole (230 V), it fits standard single-phase or split-phase sub-distribution boards. The 2 TE width leaves room for adjacent breakers.
Deployment context
Snap-on DIN-rail mounting for 35 mm rail per EN 60715. The 55 mm depth fits standard distribution enclosures without protruding into wiring ducts.