The Siemens SENTRON 3VA2340-6HN32-0BA0 is a 3-pole molded case circuit breaker rated for 400 A continuous current (Iu) at 40 °C, with no derating needed up to 50 °C — it holds the full 400 A through that range. Above 50 °C the thermal curve steps down: 385 A at 55 °C, 370 A at 60 °C, 355 A at 65 °C, and 340 A at 70 °C. That means in a warm panel enclosure you size for the ambient, not the nameplate. The interrupting ratings are the real story here: 242 kA at 240 V, 187 kA at 415 V and 440 V, 121 kA at 500 V, and 40 kA at 690 V. These are high-fault numbers — this breaker handles utility-grade available fault current without cascading upstream.
Maximum power loss is 98.5 W at rated load — account for that heat in your enclosure ventilation calculation, especially if you're grouping multiple breakers in a row.