What the ratings mean for fit
The 3VA2340-6HN42-0AA0 is a Siemens SENTRON molded case circuit breaker rated for 400 A continuous current. The ETU350 electronic trip unit provides adjustable overload and short-circuit protection curves. Thermal derating matters when the breaker lives in a warm enclosure. At 40–50 °C it holds the full 400 A; at 55 °C it derates to 385 A, at 60 °C to 370 A, at 65 °C to 355 A, and at 70 °C to 340 A. If your panel ambient runs above 50 °C, size the load current against the derated number, not the nameplate 400 A. The 4-pole configuration suits three-phase loads with a switched neutral — common in generator incomers or IT systems where neutral isolation is required.