The 400 A frame and 3-pole configuration suit main feeder or large motor branch protection in switchboards and distribution panels.
This matters when you need to clear a fault on a branch without taking the whole panel off-line.
Above that, derate linearly: 375 A at 55 °C, 350 A at 60 °C, 325 A at 65 °C, and 300 A at 70 °C. The 138 mm width and 248 mm height fit standard MCCB mounting footprints; depth is 110 mm. IP40 on the front protects against tool entry in a closed panel. Maximum power loss is 96 W — account for this in enclosure thermal calculations, especially in a crowded switchboard.