The Siemens 5SU1656-7KV25 is a combined residual current device and miniature circuit breaker (RCBO) — an FI/LS protector in Siemens' terminology. It packs Type A RCD sensitivity (300 mA) and a C-curve MCB (25 A) into a single 70 mm-wide, 1+N-pole module.
Type A detection means it catches both sinusoidal AC residual currents and pulsating DC residual currents — the kind you get from single-phase rectifiers in washing machines, LED drivers, or EV chargers. The 300 mA trip threshold is a fire-protection level, not personnel protection (30 mA is the touch-safety threshold). This unit goes into sub-circuits where you need ground-fault fire protection plus overcurrent protection in one DIN-rail slot, typically feeding socket outlets or fixed equipment in commercial kitchens, laundries, or small industrial panels. The C-curve on the 25 A MCB section means it holds 5–10× rated current for short thermal delays — sized for motor-start or capacitive inrush loads that would nuisance-trip a B-curve. At 25 A it's a fit for a 6 mm² copper circuit feeding multiple socket outlets or a small fixed load.