What it is and what it does
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. Rated 10 A at 30 °C with a B tripping characteristic, it's sized for general-purpose lighting and socket circuits where the inrush is moderate (B curve trips at 3–5× rated current). The 6 kA breaking capacity per EN 60898 and IEC 60947-2 covers most domestic and light commercial installations.
Ratings and what they mean for fit
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. If your enclosure runs hot, size the load to the derated figure, not the 30 °C label. The B curve trips between 3 and 5 times rated current — fine for resistive and most electronic loads, but a motor starting surge or transformer inrush may nuisance-trip; that's when you'd reach for a C or D curve instead. 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 6 kA breaking capacity is adequate for most residential and light commercial service entrances, but if the prospective short-circuit current at the installation point exceeds 6 kA, this unit won't clear the fault safely — check the utility's declared fault level.
Where it goes and how it mounts
Snaps onto standard 35 mm DIN rail in any mounting position. 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. Installation depth is 70 mm, overall depth 77 mm including the front of the housing. 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.