The Siemens 5SU9104-1KK40 is a SENTRON RCBO — a combined RCD and MCB in one 18 mm-wide module, rated 40 A with a C tripping curve and 10 kA breaking capacity per EN 60898 and IEC 60947-2. It protects a single-phase final subcircuit (1P+N) against overload, short-circuit, and earth leakage, sensing AC fault currents only. The 18 mm width (1 MW) means it slots into a standard DIN-rail distribution board without crowding adjacent ways.
The 40 A rating is the continuous current at 30 °C ambient; at 40 °C it derates to 37.6 A, at 45 °C to 36.4 A, at 50 °C to 34.8 A, and at 55 °C to 32.4 A (–). The C-curve means magnetic trip occurs at 5–10× In (200–400 A), suited for motor or lighting circuits with moderate inrush.
Rated for overvoltage category III. Energy limiting class 3. Touch protection integrated. Halogen-free and silicon-free construction. Storage temperature range -40 to +75 °C. Ambient operating range -25 to +45 °C.