The Siemens 5SU1656-6KV13 is a combined residual-current device (RCD) and miniature circuit breaker (MCB) — an FI/LS protector — in a single 1+N-pole unit. It integrates Type A earth-leakage detection at 300 mA IΔn with a B-curve overcurrent trip at 13 A, rated for a 6 kA breaking capacity. Type A sensitivity means it catches pulsating DC fault currents as well as sinusoidal AC, which matters for modern loads with rectified front ends (variable-speed drives, switched-mode supplies, LED drivers). The 300 mA threshold is a common specification for socket-outlet circuits in commercial and light-industrial distribution boards where a lower 30 mA trip would cause nuisance tripping on leakage from connected electronics.
The 70 mm depth (D=70 mm) is the dimension to watch when planning enclosure fill and gland-plate clearance — standard DIN-rail mounting, but the combined RCD+MCB module is deeper than a standalone MCB. The 1+N-pole format (switched phase plus switched neutral) means it occupies a single modular width on the rail, not two. For a retrofit into an existing Siemens distribution board, verify that the busbar comb profile matches the 1+N arrangement; some older boards use a 1-pole busbar that leaves the neutral terminal unconnected.