The Siemens SENTRON 5SM9625-0KK is a 2-pole residual current unit (RC unit) from the 5SM9 design series, rated 63 A at 230/400 V AC with a 300 mA tripping residual current. That 300 mA threshold puts it in the fire-protection range rather than personnel protection (which typically requires 30 mA or lower), so it's sized for branch-circuit or feeder protection where the goal is equipment and wiring insulation fault detection, not shock prevention.
Thermal derating — the real-world current capacity
The 63 A rating holds at 40 °C and 45 °C (58.59 A at both, per the spec), then starts stepping down: 56.7 A at 50 °C, 54.81 A at 55 °C, 53.55 A at 60 °C, 52.29 A at 65 °C, and 50.4 A at 70 °C. If this unit lives inside a warm panel — say next to contactors or a busbar run — the 50 °C derated figure of 56.7 A is the number to use for conductor sizing and load planning, not the nameplate 63 A. The 70 °C floor of 50.4 A tells you the thermal limit is real but not severe; the unit sheds about 20% of its rated current across a 30 °C rise.
The instantaneous design means no coordination delay with downstream RCDs — it trips at the same speed as a standard residual current device. Type AC classification limits it to sinusoidal AC fault currents; if the installation has non-sinusoidal loads (VFDs, switched-mode supplies, rectifiers), a type A or type F RC unit would be the correct choice instead.