The Siemens SENTRON 5SU9406-0KK25 is a 1P+N RCD-operated circuit breaker — an RCBO — combining overcurrent and residual-current protection in a single 18 mm wide modular unit. Rated 25 A at 30 °C with a B tripping characteristic, it interrupts fault currents up to 6 kA per EN 60898 and IEC 60947-2. The 1P+N design switches the phase and monitors the neutral, protecting one live conductor while the neutral is switched but not protected. This makes it a direct fit for single-phase final circuits in DIN-rail distribution boards where space is tight — one module width per pole saves rail length.
Ratings that govern the real application
The 25 A rating at 30 °C is the headline number, but the derating curve matters more in a warm panel: at 40 °C it's 23.5 A, at 45 °C it's 22.75 A, at 50 °C it's 21.75 A, and at 55 °C it's 20.25 A. If your enclosure ambient runs above 40 °C, size the circuit for the derated current — not the 25 A sticker. The B curve (3–5 In instantaneous trip) suits resistive and general-purpose loads — lighting, small appliances, control transformers — where inrush is low. For motor or capacitor loads, a C or D curve would be the better call.
One modular width (18 mm) per unit, 77 mm depth, 125 mm height. Installation depth is 70 mm — factor that into enclosure depth, especially with wiring ducts.