The 5SL7240-7RC: The 15 kA breaking capacity at 415 V means this MCB can safely interrupt a fault current up to that level without welding its contacts or failing catastrophically — that's the rating you match against the prospective short-circuit current (PSCC) at the panel's supply point. The C-curve (magnetic trip between 5 and 10 times In) is the standard for moderate inrush loads like small motors, transformers, and lighting banks; it holds through the starting surge without nuisance tripping on a 40 A circuit. Two-pole construction switches both phase conductors simultaneously, which you need for single-phase 240 V line-to-line or a 415 V two-phase load.
Standard DIN-rail mount, 2 modules wide. Wires up clean with a screw-clamp terminal accepting 1–25 mm² conductor. The 40 A rating suits it for a sub-feed or a larger branch circuit in a distribution board — think a small pump, a compressor, or a lighting sub-panel where the C-curve keeps it from popping on the inrush.