400 A MCCB with 242 kA interrupting — what you're actually getting
That 400 A holds all the way to 50 °C ambient — no derating until you push past 55 °C, where it steps down to 375 A at 55 °C, 350 A at 60 °C, 325 A at 65 °C, and 300 A at 70 °C. The interrupting capacity is the headline: 242 kA at 240 V, dropping to 187 kA at 415 V and 440 V, 121 kA at 500 V, and 7.5 kA at 690 V.
Panel fit and thermal management
The 96 W maximum power loss means it throws heat into the enclosure; if you're packing several of these in a single panel, factor that into your ventilation or derating calculation.
The 400 A continuous rating at 40-50 °C is what governs feeder sizing — a 400 A bus or cable set.