The 15 kA interrupting rating at 400 V gives the selectivity headroom needed in a distribution board feeding multiple downstream sub-circuits; it clears a bolted fault before the upstream device has to act, keeping the rest of the board live.
Integration note
Snap-on DIN rail mounting, standard 1-pole width per phase (3 modules plus neutral). The D1 rating (1 A) governs the thermal-magnetic trip threshold: the thermal element holds continuous current up to 1 A, and the magnetic trip operates at 10 to 20 times rated current for short-circuit protection. In a panel, verify the neutral conductor is connected through the switched pole — this is a 3P+N device, not a 4-pole unit with a fully rated neutral pole.