The Siemens 5SM1111-6BA is a Type A residual current device (RCD) — what Siemens calls an FI Protector — rated 16A, 2-pole, with a 10 mA trip sensitivity at 230 V. The Type A classification means it detects pulsating DC fault currents on top of sinusoidal AC, which covers most modern electronic loads like switched-mode power supplies, VFDs, and single-phase rectifiers. The 10 mA IΔn is the high-sensitivity end of the scale — it catches leakage currents well below what a 30 mA unit would pass, so it's typically specified for circuits where direct contact with live parts is a realistic risk (e.g., hand-held tools in a wet environment, or medical locations). The 16 A rated current matches standard 16 A final subcircuits in IEC 60364.
Two modules wide (36 mm), so it replaces a standard 2-pole MCB slot. Wires up with the incoming phase and neutral through the top terminals, load out the bottom. The 55 mm depth (D=55mm) fits flush in most domestic and light-commercial consumer units without hitting the enclosure lid.