What it is and what the ratings mean
The Siemens 5SU1356-1DA06 is a combined residual-current and miniature circuit breaker (RCBO) — an FI/LS protector — in a 1+N-pole format. The Type AC (WS) designation means it detects sinusoidal AC fault currents only; the 30 mA trip sensitivity is the standard for personal protection against electric shock in residential and commercial final circuits. The 6 kA breaking capacity tells you it can safely interrupt a fault current up to 6 kA at the rated voltage, which covers the prospective short-circuit current at most distribution board positions in a building installation. The C-curve (6 A rated current) means the magnetic trip activates at 5–10× In, so it handles motor inrush and capacitive loads without nuisance tripping while still clearing a hard short. The pig-tail neutral connection is a factory-fitted flexible lead, not a busbar stab — factor that into your panel wiring plan.
Where it fits in the panel
The 70 mm depth (D=70MM) is the dimension from the DIN-rail mounting surface to the front of the device — standard for Siemens 5SU series RCBOs. It snaps onto a 35 mm DIN rail per EN 60715 in a distribution board. The 1+N-pole width occupies a single modular unit (roughly 18 mm per pole, but confirm the exact width from the product drawing for your busbar layout). The pig-tail neutral exits the bottom; plan your neutral busbar routing accordingly to keep the bend radius within the enclosure's wiring space.