What this 400 A MCCB does on the line
It carries an ETU330 electronic trip unit — that's the brain that gives you adjustable long-time, short-time, and instantaneous pickup curves, plus ground-fault protection via summation current sensing on the L-conductor.
Thermal derating — the real-world current you can actually run
At 55 °C it drops to 385 A, at 60 °C to 370 A, at 65 °C to 355 A, and at 70 °C to 340 A. If you're packing this into a hot panel next to drives or transformers, you need to check the ambient at the breaker's location — not the room thermostat.
That's about 9.76 by 5.43 by 4.33 inches. The front face carries an IP40 protection class — fine for a closed panel, but don't leave the door open in a washdown area. It's a straight line-protection MCCB with ground-fault monitoring built into the trip unit. The power loss at full rated current is 96 W, so factor that into your panel thermal budget.