What this 400 A MCCB is built for
It carries a rated insulation voltage of 800 V and delivers a short-circuit breaking capacity of 187 kA at 240 V, 121 kA at 415 V, and 75.6 kA at 500 V — numbers that tell you it's sized for high-fault main feeders, not branch circuits. Thermal derating matters when you pack this into a closed panel: it holds full 400 A up to 50 °C ambient, then steps down to 385 A at 55 °C and 340 A at 70 °C. That curve is the difference between a breaker that holds and one that nuisance-trips on a hot summer shift.
The 3VA2340-5HL42-0JL0 measures 184 mm wide by 248 mm high by 110 mm deep — a four-pole frame that needs real estate on the DIN rail or mounting plate. At 96 W maximum power loss, plan for ventilation or forced cooling in a densely packed enclosure; that heat has to go somewhere.