What it is and what it does
The Siemens 5SU9356-2CN16 is a combined residual current and overcurrent protective device (RCBO) in a 1+N pole format. It provides both earth leakage protection and short-circuit/overload protection in a single DIN-rail module, sized for final sub-circuits in commercial or industrial distribution boards. Rated at 16 A with a D tripping characteristic, this RCBO handles inrush currents common to motor and transformer loads — the D curve delays the magnetic trip to avoid nuisance tripping on start-up. The 6 kA breaking capacity covers standard domestic and light commercial fault levels. The residual current element is type AC, meaning it detects sinusoidal AC earth faults only. That covers basic socket-outlet and lighting circuits; for pulsed DC or smooth DC fault currents you would need a type A or type B device instead.