What this 400 A MCCB does for your main feeder
The Siemens 3VA2340-6JQ32-0AG0 is a 3-pole SENTRON molded case circuit breaker rated for 400 A continuous (Iu) with an ETU560 electronic trip unit. It's built for line protection on a main feeder or large subfeed — the kind of breaker that sits between your transformer and the distribution bus, where you need adjustable long-time, short-time, instantaneous, and ground-fault protection in one package. The interrupting ratings are serious: 242 kA at 240 V, 187 kA at 415 V and 440 V, 121 kA at 500 V, and 40 kA at 690 V — so it handles high available fault current without cascading upstream. This breaker includes a communication function and comes with one auxiliary switch plus one trip alarm switch. That means it can report its status back to a PLC or BMS — useful for a motor control center or switchgear lineup where you want remote indication of trip events without adding separate control relays. The ETU560 trip unit gives you adjustable protection curves and a local trip indicator so when it does open, you know why.
How it fits in a panel
Dimensions are 248 mm high, 138 mm wide, 110 mm deep — a standard 3-pole MCCB footprint for this class. Mounts on a DIN rail or direct to a backplate with the supplied hardware. The 110 mm depth is worth checking against your enclosure depth, especially if you're retrofitting into an existing panel that was spec'd around a different breaker like the 5SQ2370-2YA05 family; the Siemens sits shallower than some older frames, so gland-plate clearance is usually fine, but always confirm the bus-bar connection points line up with your existing risers.
Thermal derating — what 400 A really means at your ambient
The 400 A continuous rating holds from 40 °C up to 50 °C — no derating needed in a typical panel that stays under 50 °C. At 55 °C it's still good for 375 A, at 60 °C for 350 A, and so on down to 300 A at 70 °C. If your switchroom runs hot, this gives you a clean derating curve to work with instead of guessing.