What it is and what it does
The Siemens 5SU9404-1KK06 is a 1P+N RCD-operated circuit breaker (RCBO) from the SENTRON 5SU9 series, combining overcurrent protection and residual current detection in a single 18 mm wide module. Rated 6 A at 30 °C with a Type C tripping characteristic, it handles moderate inrush loads like small motors or lighting banks. The integrated RCD trips on AC fault currents, so it's suited for circuits where both short-circuit and earth-fault protection are needed in one device. Breaking capacity is 10 kA per EN 60898 and IEC 60947-2, meaning it can safely interrupt fault currents up to that level without upstream damage. The 10 kA rating is typical for sub-distribution boards in commercial or light industrial panels.
Thermal derating and conductor sizing
The 6 A rating holds at 30 °C ambient; at 40 °C it derates to 5.64 A, at 45 °C to 5.46 A, at 50 °C to 5.22 A, and at 55 °C to 4.86 A. If the panel ambient runs above 30 °C, factor the derated current into the load calculation — the 6 A nameplate is not the limit in a warm enclosure. Terminals accept solid or stranded conductors from 0.75 mm² up to 35 mm², which covers most branch-circuit wiring sizes. The 18 mm width (1 width unit) and 70 mm installation depth fit standard DIN-rail enclosures; mounting position is unrestricted.
Compliance and approvals
Rated for overvoltage category III and touch-protected per the product feature. Halogen-free and silicon-free construction. Ambient operating range -25 to +45 °C; storage from -40 to +75 °C. IP20 rating applies when installed in a distribution board with connected conductors.