The Siemens SENTRON 5SU9306-0KK25 is an RCD-operated circuit breaker (RCBO) combining overcurrent and residual current protection in a single 18 mm wide unit. Rated 25 A at 30 °C with a B tripping characteristic, it handles AC fault currents and provides 6 kA breaking capacity per EN 60898 and IEC 60947-2. The 1P+N configuration protects one live pole while switching the neutral.
What the ratings mean for fit
The 25 A rating at 30 °C is the headline figure, but the derating curve matters in a warm panel: at 40 °C it carries 23.5 A, at 45 °C it drops to 22.75 A, and at 55 °C it's 20.25 A. If your enclosure ambient sits at 45 °C, size the load to 22.75 A continuous, not the 25 A nameplate. The B curve trips between 3 and 5 times rated current — expect instantaneous trip at roughly 75–125 A, which is typical for resistive or lighting loads with modest inrush. The 6 kA breaking capacity per EN 60898 and IEC 60947-2 means this RCBO can safely interrupt a fault current up to 6 kA at the rated voltage. In a domestic or light commercial distribution board with a typical upstream fuse or MCB rated 6 kA or less, it coordinates without requiring a current-limiting device upstream. Overvoltage category III confirms it's rated for fixed installation downstream of the utility meter.
Panel integration and wiring
At 18 mm wide (1 width unit), the 5SU9306-0KK25 snaps onto a standard DIN rail. Installation depth is 70 mm, overall depth 77 mm — verify clearance to the enclosure door or gland plate. The terminal accepts solid or stranded conductors from 0.75 mm² up to 35 mm², which covers most downstream cable sizes for a 25 A circuit. Supply can enter from either top or bottom, which simplifies busbar routing in a crowded board. Mounting position is unrestricted, so it can be installed horizontally or vertically without derating. The IP20 rating applies only when the distribution board is installed and conductors are connected — treat it as a panel-internal device, not for standalone outdoor use. Touch protection is built in (fingertip-safe terminals).