What this 400 A MCCB carries
The Siemens SENTRON 3VA2340-5JP42-0AA0 is a 4-pole molded case circuit breaker rated for 400 A continuous current at 40 °C, with an ETU550 electronic trip unit. The 800 V rated insulation voltage means it's built for 690 V industrial systems, though the 7.5 kA at 690 V is the limit there. The 184 mm width and 248 mm height fit the standard SENTRON 3VA panel cutout. Depth is 110 mm. IP40 on the front — fine for a dry indoor switchboard, not for washdown.
Above that it drops: 375 A at 55 °C, 350 A at 60 °C, 325 A at 65 °C, and 300 A at 70 °C. If your panel ambient runs 55 °C, size the load at 375 A max. The 96 W max power loss is the heat it dumps into the enclosure — factor that into your ventilation calcs.