The Siemens 5SU1656-6KV16 is an FI/LS combination unit — a residual current device (RCD) and miniature circuit breaker (MCB) in one 1+N-pole module. It's a Type A RCD with a 300 mA trip sensitivity paired with a B-curve 16 A overcurrent protector, rated for 6 kA breaking capacity. That 300 mA IΔN means it's sized for general socket-outlet and lighting circuits where nuisance tripping from small leakage currents (like electronics or surge suppressors) needs to be avoided, rather than for personal shock protection which demands 30 mA. The B-curve 16 A trips between 3 and 5 times rated current, so it handles resistive and moderate inductive loads without nuisance trips from inrush.
Panel fit and deployment
The D=70mm dimension is the unit's width in millimeters — 70 mm wide, which is 4 standard DIN-rail module widths (each 17.5 mm). That's the panel space it occupies in the distribution board. Type A RCD detection covers sinusoidal AC residual currents plus pulsating DC residual currents up to 6 mA, which is what you get from single-phase rectifiers in switched-mode power supplies, LED drivers, or washing machine electronics. The 6 kA breaking capacity (Icn) is the short-circuit rating per IEC 61009-1; it interrupts faults up to that level without needing an upstream backup fuse, provided the prospective short-circuit current at the installation point doesn't exceed 6 kA.