The Siemens SENTRON 5SL6140-6 is a 1-pole miniature circuit breaker rated 40 A with a B tripping characteristic and 6 kA breaking capacity per both EN 60898 and IEC 60947-2. That 6 kA figure is the short-circuit rating that governs panel coordination — it tells you this MCB safely interrupts faults up to 6 kA at 400 V AC without upstream cascading.
Snaps onto standard DIN rail, occupies one modular width (18 mm). Depth is 76 mm with 70 mm installation depth — verify gland-plate clearance if your enclosure has a shallow back panel. Mounting position is unrestricted, which helps when routing conductors in tight layouts.