What it is and what it does
The Siemens 5SU9356-1KN25 is a 2-pole (1P+N) RCD-operated circuit breaker from the SENTRON family, combining overcurrent and residual current protection in a single 36 mm-wide module. It is rated 25 A at AC with a 30 mA residual current trip and a Type C tripping characteristic, making it suitable for protecting final circuits against both overload/short-circuit and earth faults in residential or commercial distribution boards.
Key ratings and what they mean for fit
The 25 A rating at 30 °C is the base current; 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 ambient runs above 30 °C, the load must be reduced accordingly — a 20 A circuit at 55 °C is the practical ceiling. The breaking capacity is 6 kA per EN 60898 and 10 kA per IEC 60947-2, meaning it can safely interrupt fault currents up to those levels. The 30 mA residual current is the standard for personal protection against indirect contact. The Type C characteristic handles moderate inrush from motor or lighting loads without nuisance tripping.
Mounting and integration
Occupies 2 modular width units (36 mm) on a DIN rail. Installation depth is 70 mm, overall depth 77 mm. Mounting position is any; supply can enter from top or bottom. IP20 with connected conductors — standard for enclosed distribution boards. Touch protection is provided. Halogen-free and silicon-free construction suits environments sensitive to corrosive off-gassing, such as data centers or clean rooms.