It's not a general-purpose branch breaker; it's built to sit ahead of a motor starter, coordinating with the contactor to clear faults without welding the contacts. At 690 V it still interrupts 3 kA, so it handles the high-voltage end of a 690 V line without cascading upstream.
The 55 mm width and 149 mm depth mean it occupies one standard 55 mm module on the rail — check your enclosure fill factor if you're packing multiple starters into a shallow panel. Clearance requirements: 50 mm upwards and downwards, 10 mm to the side, zero forwards or backwards. That's tight enough for dense layouts but the 50 mm vertical gap matters for airflow in a sealed enclosure running at 60 °C ambient.