Its full-scale rating is 400 A, with an adjustable trip range from 600 A minimum to 4 000 A maximum, so you set the actual protection threshold to match the downstream load without swapping the breaker frame. At 240 V it interrupts 187 kA; at 415 V and 440 V it holds at 121 kA; at 500 V it drops to 75.6 kA; and at 690 V it still clears 7.5 kA. It carries a full 400 A from 40 °C through 50 °C, then steps down: 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 tells you how many of these fit across a standard 600 mm wide panel — four with some air gap, three comfortably. Max power loss is 98.5 W at full load. That heat has to be vented or conducted out of the enclosure — if you pack several of these in a sealed cabinet, the internal temperature rise will push you into the derating curve above 50 °C.
The 80 A initial value on the trip unit means the breaker ships with the trip threshold set at 80 A — you adjust it up to the 400 A full-scale during commissioning.