The Siemens 5SU9356-2CN40 is a 1+N RCBO (residual current circuit breaker with overcurrent protection) rated for 40 A with a 6 kA breaking capacity. The D characteristic means it's designed for loads with high inrush currents — think motor starters, transformers, or welding equipment where the start-up spike would trip a B or C curve. The 'type AC' detection handles sinusoidal AC residual currents only; if your circuit has pulsed DC or smooth DC fault currents (variable-speed drives, UPS systems), you'd want a type A or F instead.
What the Ratings Mean for Fit
The 6 kA breaking capacity at the rated voltage is the maximum fault current this device can safely interrupt — sufficient for most residential and light commercial distribution boards where the prospective short-circuit current stays under that threshold. The D-curve trip threshold (10–20× In) delays tripping long enough for motor-starting or capacitor-bank inrush to pass without nuisance trips. The 1+N configuration switches the line conductor and disconnects the neutral but does not protect the neutral against overcurrent; it's the standard arrangement for single-phase final circuits in many European and Asian markets.
Panel Integration
This RCBO snaps onto a standard DIN rail (EN 60715) inside a distribution board or sub-panel. The Construction line designation indicates it's built for the residential and commercial building market — compact module width, finger-safe terminals, and a busbar-compatible connection system for multi-pole grouping. Verify the busbar pitch matches your panel's layout before committing the assembly.