What it is and what the ratings mean
The Siemens 5SU1656-1KV25 is a combined residual current device and miniature circuit breaker (RCBO) in a single 1+N-pole module, Type AC sensitivity, rated at 25 A C-curve overcurrent protection and 300 mA residual trip threshold. The 6 kA breaking capacity at the listed voltage covers most domestic and light commercial sub-distribution boards where the prospective fault current stays under that level. Type AC detection means it responds to sinusoidal AC earth faults only — not pulsed DC or smooth DC residuals, so it belongs on circuits without variable-speed drives, UPS feeds, or EV chargers downstream.
Panel integration and deployment context
The 70 mm depth (D=70mm per the description) fits standard DIN-rail enclosures; the 1+N-pole format occupies a single module width on the rail, leaving room for adjacent MCBs or contactors in a crowded consumer unit or sub-distribution board. Rated for 50/60 Hz networks, it is the go-to RCBO for general-purpose socket circuits, lighting, and resistive loads in residential or commercial final sub-circuits where the earth-fault path is pure AC.