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).
Deployment context and panel fit
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.