The Siemens 5SU1653-6KV40 is a combined residual current device and miniature circuit breaker — an RCBO — in a single 1+N-POL module. The 300 mA residual sensitivity is sized for fire protection rather than personal shock protection — it will not catch a 30 mA body-contact fault, but it prevents cable insulation deterioration from becoming a fire risk in distribution circuits. The 70 mm depth (D=70MM) fits standard distribution boards; the 1+N-POL form factor occupies one modular width for the live pole plus a switched neutral, which is typical for single-phase final circuits in TN-S or TN-C-S systems. Snap it onto DIN rail in the enclosure.
For a BOM freeze or critical-spare holding, the 5SU1653-6KV40 is available to order. No need to stockpile against an EOL — but if you are maintaining a legacy panel that already has this exact code, keeping one in the cabinet is cheap insurance before a failure.