The Siemens 5SU1656-1KV32 is a combined residual-current and overcurrent protective device (RCBO) — an FI/LS protector in Siemens' 5SU1 series.
The 300 mA sensitivity is a fire-protection threshold (not personal shock protection), so it goes on submain or distribution circuits where 30 mA nuisance tripping is a concern. The C-curve 32 A overcurrent characteristic handles motor-starting inrush and moderate inductive loads without nuisance trips on transformer or capacitor bank energisation. The 6 kA breaking capacity (Icn) at 230/400 V is the standard domestic and light commercial rating per IEC 61009-1. In a panel with a higher prospective fault current (above 6 kA), this unit needs an upstream current-limiting device — typically a 63 A gG fuse or a higher-rated MCB — to keep the let-through energy within its rated short-circuit capacity. The 1+N-pole form factor (switched phase, switched neutral) occupies a single 70 mm wide module on the DIN rail, matching the standard Siemens 5SU1 family footprint.
The part is not a short-run or niche variant; it is a standard catalogue RCBO that replenishes on normal lead times.