400 A MCCB with ETU350 — what the ratings mean for your panel
The Siemens SENTRON 3VA2440-5HN32-0AE0 is a 3-pole molded case circuit breaker rated for 400 A continuous current (Iu) with an ETU350 electronic trip unit. At 240 V it interrupts 187 kA; at 415 V and 440 V that drops to 121 kA, then 75.6 kA at 500 V, and 17 kA at 690 V — so the available fault current at your service voltage is the number that governs SCCR compliance, not the 240 V headline. The ETU350 provides adjustable long-time, short-time, instantaneous, and ground-fault protection curves, which means you can coordinate downstream feeders without nuisance tripping on motor inrush. Rated insulation voltage is 800 V (Ui), and the breaker carries a maximum power loss of 63.5 W — relevant for enclosure thermal rise calculations when grouping several breakers in a single panel. The 138 mm width, 248 mm height, and 110 mm depth fit the standard SENTRON 3VA footprint, so a panel laid out for a 3VA frame accepts this unit without re-drilling the mounting plate.
Temperature derating — don't lose capacity at the bus
The 400 A rating holds at 40 °C, 45 °C, and 50 °C ambient. At 55 °C it derates to 384 A, at 60 °C to 376 A, at 65 °C to 368 A, and at 70 °C to 360 A. If your panel ambient runs above 50 °C — common in enclosed switchgear with multiple heat sources — size the breaker one frame up or verify the actual load current against the derated figure. Operating range is -25 °C to 70 °C; storage range is -40 °C to 80 °C.