What this part is and what the ratings mean
The Siemens 5SU1653-6KV10 is a combined residual-current device and miniature circuit breaker (RCBO) — an FI/LS protector in Siemens' own shorthand. It packs a Type A RCD (sensitive to pulsating DC fault currents up to 6 mA smooth DC, per IEC 60755) and a B-curve MCB into a single 1+N-Pol module. The 300 mA residual trip threshold means it's sized for protection against fire risk from earth faults rather than personnel shock protection (that's the 30 mA version's job). The 4.5 kA breaking capacity covers the typical prospective short-circuit current at the distribution board in most residential and light commercial installations. The B-curve 10 A overcurrent element trips between 3 and 5 times rated current — fast enough for resistive and lighting loads, but not for motor starting inrush.
Deployment context and panel fit
This RCBO snaps onto a standard 35 mm DIN rail inside a distribution board or sub-distribution panel. The 70 mm depth (D=70 mm) is standard for Siemens 5SU series devices, so it sits flush with adjacent breakers and RCDs. The 1+N-Pol construction switches and protects the phase conductor only; the neutral bar passes through the residual-current transformer but is not switched — verify your neutral bar arrangement in the panel before committing the BOM line.