The Siemens SENTRON 5SU9406-0KK10 is a combined RCD and miniature circuit breaker (RCBO) in a single 18 mm wide module — one width unit on the DIN rail. It protects against both overcurrent/short-circuit and earth leakage in a single device, saving a slot in the panel compared to separate MCB + RCD.
The 10 A rating at 30 °C is the headline number, but the derating curve matters more in a warm panel: at 40 °C it's 9.4 A, at 45 °C it's 9.1 A, at 50 °C it's 8.7 A, and at 55 °C it's 8.1 A. This is a 1P+N device — it switches the line conductor and breaks the neutral, but the neutral pole is not protected against overcurrent. The RCD element is type AC, meaning it detects sinusoidal AC earth fault currents only. For pulsating DC or smooth DC fault currents (common with VFDs, EV chargers, or modern electronics), you'd need type A or F.
The 18 mm width (one width unit) means it occupies a single slot in a consumer unit or distribution board. Accepts solid or stranded conductors from 0.75 up to 35 mm² — covers everything from 1.5 mm² lighting circuits up to 10 mm² submains. Supply can enter from top or bottom, which simplifies busbar layout. IP20 when installed in a distribution board with conductors connected — not for wet locations.