What the ratings mean for fit
The Siemens 3VA2440-6HN42-0AA0 is a 4-pole SENTRON molded case circuit breaker (MCCB) rated for 400 A continuous current at 40 °C ambient, with an ETU350 electronic overcurrent release. The 400 A rating holds flat through 50 °C — only above that does it start to derate, dropping to 388 A at 55 °C and 352 A at 70 °C. So if your panel ambient runs at 55 °C, you're still good for a 388 A continuous load, not the full 400 A. The breaking capacity tells you where this breaker is comfortable: 242 kA at 240 V, 187 kA at 415 V, 85 kA at 440 V, 55 kA at 500 V, and 9 kA at 690 V. That 242 kA at 240 V is a monster — it's sized for high-fault transformer secondaries or large motor control centers where the available fault current is extreme. At 690 V the 9 kA is modest, so know your system voltage and fault level before committing.
Panel integration and footprint
The 3VA2440-6HN42-0AA0 measures 184 mm wide by 248 mm high by 110 mm deep. That 184 mm width for a 4-pole 400 A frame is typical for this class — it's a 4-module-wide footprint on the DIN rail or bolted to the backplate. The IP40 front protection means it's fine in a clean indoor panel; no washdown rating, so keep it behind the gland plate. Maximum power loss is 63.3 W, which matters for thermal management inside a sealed enclosure — that's heat that has to be vented or dissipated. Storage range is -40 °C to 80 °C; operating range is -40 °C to 70 °C, so it handles cold warehouses and hot panels alike.
ETU350 trip unit and protection capabilities
The ETU350 is an electronic trip unit with adjustable long-time pickup and delay. The long-time delay (tr) is adjustable from 0.5 s to 17 s, which lets you coordinate with downstream breakers and upstream transformers. The N-conductor protection is adjustable — OFF, 50%, or 100% of the phase pickup — so you can set it for a reduced neutral or full-rated neutral depending on the system. No ground-fault monitoring on this version (the 'Without' designation), so if you need GF protection, you'll add an external module or pick a different variant. The latching endurance is rated at 15,000 cycles, which is standard for a distribution MCCB — not a switching device, but fine for occasional manual operation or maintenance isolation.