What this 400 A MCCB delivers — and what to watch
The Siemens SENTRON 3VA2340-6JQ32-0JH0 is a 3-pole molded case circuit breaker rated for continuous 400 A at 40 °C ambient — that's the headline number for sizing a feeder or main. It holds that same 400 A all the way up to 50 °C, then derates linearly to 300 A at 70 °C, so if your panel runs hot you still have headroom without upsizing the frame. Interrupting capacity is the real selector here: 242 kA at 240 V, 187 kA at 415/440 V, 121 kA at 500 V, and 7.5 kA at 690 V. That 242 kA figure at 240 V means it can sit on a high-fault transformer secondary without cascading upstream — useful for a main breaker in a 240 V delta or 277/480 V wye panel where the available fault current is north of 100 kA. This is a line-protection design (not motor-protection), so the trip curve is set for cable and bus protection. It ships with a shunt trip (STL) and two auxiliary switches plus a separate trip-alarm switch — that alarm contact closes only on a fault trip, giving a clean signal to a PLC or annunciator without tying up an aux contact.
Panel fit and integration
Dimensions: 248 mm height, 138 mm width, 110 mm depth — that's a 9.76 x 5.43 x 4.33 inch footprint. It mounts on a DIN rail or directly to a backplate via the screw terminals. The 138 mm width means it occupies three 45 mm pole spaces, standard for a 3-pole MCCB in a distribution board. Leave at least 50 mm clearance above and below for arc-chamber venting and cable bending radius. Power loss is 96 W maximum at rated current. That's not trivial — in a sealed, non-ventilated enclosure, that heat has to be factored into the thermal budget. If you are packing multiple breakers side by side, derate per the manufacturer's grouping factors or add forced ventilation.