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. Its interrupting capacity hits 187 kA at 240 V and 121 kA at 415 V — enough to handle high-fault utility feeds or transformer secondaries without cascading upstream. 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. Designed for line protection, not motor or generator duty. 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. The ETU550 release gives you adjustable long-time, short-time, instantaneous, and ground-fault protection curves; the communication function means it can talk to a BMS or PLC via the SENTRON powerconfig bus.
Thermal derating — the real continuous current
The 400 A rating holds flat from 40 °C to 50 °C. 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.