What this MCCB does on the line
It handles fault currents up to 187 kA at 240 V and 121 kA at 415 V or 440 V — that's the interrupting capacity that clears a bolted fault before the upstream gear takes damage.
Rating so-what for the panel
The 3-pole form factor fits standard MCCB mounting footprints.
Thermal derating matters in a hot panel
The 400 A rating holds up to 50 °C ambient; above that it derates linearly — 385 A at 55 °C, 370 A at 60 °C, 355 A at 65 °C, and 340 A at 70 °C. Max power loss is 96 W, so ventilation matters in a sealed enclosure.