What this 4-pole 16 A C-curve MCB does on the rail
The IP20 finger-safe enclosure suits it for enclosed distribution boards; the 55 mm installation depth and 3 width-unit (roughly 54 mm) footprint fit standard DIN-rail enclosures.
The 3 width-unit body (each unit is 18 mm, so 54 mm total) and 55 mm installation depth leave clearance for standard enclosure depths of 80 mm or more. The switched-neutral function (3P+N) means the neutral pole opens and closes with the phases — important for TN-S or TN-C-S systems where isolating the neutral during maintenance is required. Overvoltage category 3 and energy limiting class 3 indicate it's designed for fixed-installation distribution boards, not for direct motor starting.