What this 400 A MCCB is and where it lands
The Siemens 3VA1340-7GF42-0AA0 is a SENTRON molded case circuit breaker (MCCB) — line protection version, 4-pole, carrying 400 A continuous at 40 °C without derating. That 400 A holds steady up through 50 °C; at 55 °C it's 392 A, and at 70 °C still 367 A (–). The TM240 thermal-magnetic release handles the overload and short-circuit curves. On the interrupting side, it's rated 440 kA at 240 V AC, 242 kA at 415/440 V, 154 kA at 500 V, and 17 kA at 690 V (–). That kind of short-circuit capacity says this breaker is meant for high-fault locations — main feeders, transformer secondaries, or large bus risers where the available fault current is serious. It lives on a DIN rail or direct-mount in a panel; the 184 mm width and 110 mm depth (–) mean it fits standard MCCB cubicle cutouts, but verify the mounting centers if you're swapping into an older footprint.
What the key ratings mean for fit
The 400 A continuous rating at 40 °C is the headline number for sizing — it's the breaker's uninterrupted current-carrying capacity in a 40 °C ambient. If your panel ambient runs hotter, the derating curve is published: 392 A at 55 °C, 384 A at 60 °C, 376 A at 65 °C, 367 A at 70 °C (–). The TM240 release means the thermal element is calibrated for a 400 A frame with a 240 A rating plug — verify the actual trip setting matches your load's FLA. The 440 kA interrupting rating at 240 V is the SCCR you can claim downstream; at 690 V it drops to 17 kA, so if you're feeding a 690 V drive or transformer, the available fault current must be coordinated. The 4-pole design with 100% N-conductor protection means the neutral is fully rated and switched — essential for 4-wire systems where harmonic currents or unbalanced loads could overload a reduced-neutral path. Front IP40 is standard for indoor panel mounting; no washdown rating, so keep it behind a gland plate.