The Siemens 5SU1656-7KK25 is a SENTRON-series RCBO (residual current circuit breaker with overcurrent protection) combining a 25 A overcurrent trip (C-curve, 1P+N) with a 300 mA Type A residual current device in a single 2-module-width package.
The 25 A rating at 30 °C is the headline thermal current; at elevated panel temperatures the device derates — 23.5 A at 40 °C, 21.75 A at 50 °C, and 18.25 A at 70 °C. If the distribution board sits in a warm environment (e.g., adjacent to a boiler or in a non-climate-controlled enclosure), use the 40 °C or 50 °C column for sizing, not the 30 °C figure. It is not suitable for smooth DC fault currents — that would require Type B. For general-purpose final circuits with electronic loads, Type A is the standard choice.
It mounts in any position and accepts supply from either top or bottom.