What this FI/LS protector carries
The Siemens 5SU1653-0KV40 is a Type AC residual current device with integrated miniature circuit breaker — an FI/LS combination unit in a 1+N-POL form factor. It combines a 40 A B-curve MCB with a 300 mA RCD, rated for 4.5 kA breaking capacity. The 300 mA sensitivity is sized for fire protection and general equipment protection rather than personal shock protection (which typically requires 30 mA or less).
The 70 mm depth (D=70MM) fits standard DIN-rail enclosures with typical gland-plate clearance. The 1+N-POL arrangement occupies a single modular width on the rail, with the neutral pole switched internally. The B-curve trip characteristic (3-5 In) suits resistive and general-purpose loads — lighting, small motor circuits, and control transformers — where inrush is moderate.