The Siemens 5SU9304-7KK25 is a 1P+N RCD-operated circuit breaker (RCBO) from the SENTRON 5SU9 series, combining overcurrent protection and residual current detection in a single 18 mm wide module.
Thermal derating and conductor sizing
The 25 A rating holds at 30 °C ambient; at 40 °C it derates to 23.5 A, at 45 °C to 22.75 A, at 50 °C to 21.75 A, and at 55 °C to 20.25 A. If the panel runs warm — say near a transformer or drive — size the load accordingly. Power dissipation is a modest 0.75 W at rated load, so heat buildup in a crowded enclosure is minimal.
Mounting position is unrestricted — horizontal, vertical, upside-down, it doesn't care. Supply can feed from top or bottom. IP20 with the distribution board installed and conductors connected; touch protection is built in.