400 A MCCB with TM240 release — what the ratings mean for your panel
The Siemens 3VA1340-6GF42-0AA0 is a SENTRON molded case circuit breaker rated for 400 A continuous current at 40 °C through 50 °C, with no derating needed in that band. Above 55 °C the thermal curve begins to pull back: 392 A at 55 °C, 384 A at 60 °C, 376 A at 65 °C, and 367 A at 70 °C. That matters if your enclosure runs hot — you lose roughly 2 % per 5 °C above 50 °C, so a panel at 65 °C derates the breaker to 376 A, and the downstream load must be sized accordingly. The interrupting ratings are the headline: 220 kA at 240 V, 154 kA at 415 V and 440 V, 121 kA at 500 V, and 17 kA at 690 V. For a 400 A frame, 220 kA at 240 V is high-end — it handles fault currents at the transformer secondary without cascading upstream. The 17 kA at 690 V is the weak point; if your system runs 690 V with available fault current above that, you need a current-limiting upstream device or a higher-rated frame.
TM240 overcurrent release and line protection design
The overcurrent release is designated TM240 — a thermal-magnetic type tuned for line protection (cable, busbar, distribution). That means the thermal element handles overloads with an inverse-time curve, and the magnetic element handles short-circuits instantaneously. It is not a motor-protection breaker (no adjustable magnetic pickup for inrush), so it belongs in a distribution board or feeder circuit, not directly upstream of a motor starter. Rated insulation voltage is 800 V, so the breaker is suitable for 690 V systems with margin. Maximum power loss is 92.1 W at rated current — that heat must be vented in a sealed enclosure. Front protection is IP40, meaning tools and fingers are kept out, but the sides and back rely on the panel enclosure for IP rating.
Physical fit and panel integration
Dimensions: 248 mm height, 184 mm width, 110 mm depth. The 4-pole body is 184 mm wide — that is the standard 4-pole MCCB footprint for a 400 A frame, so it fits existing cutouts and busbar spacing designed for that class. Depth at 110 mm is shallow enough for most 300 mm deep enclosures with wiring space behind. No undervoltage release, no shunt trip, no communication module, and no ground-fault monitoring on this variant. If your circuit requires UVR or GF protection, you need a different suffix in the 3VA1 series. The TM240 release is fixed — no interchangeable trip units on this order code.