What this 320 A MCCB carries — and where it holds the line
The Siemens SENTRON 3VA1332-5MH32-0AA0 is a 3-pole molded case circuit breaker rated for a continuous 320 A — and it holds that full rating from 40 °C right through 50 °C ambient, which is the real-world panel temperature for most industrial switchboards. Above that, the thermal derating is modest: 313 A at 55 °C, 306 A at 60 °C, 299 A at 65 °C, 292 A at 70 °C. That means you can load it at nameplate in a ventilated enclosure without having to oversize the frame for ambient headroom. The TM120M thermal-magnetic release provides fixed thermal and magnetic trip settings — no adjustment dials, no interchangeable trip units. For a protection engineer, that is a deliberate choice: the trip curve is locked at the factory, eliminating the risk of a field-adjustment error that could mis-coordinate with downstream breakers. The trade-off is that you cannot re-range it for a different cable size or motor FLA without swapping the entire breaker. Breaking capacity is where this frame earns its place in a high-fault installation: 187 kA at 240 V, 121 kA at 415 V and 440 V, 75.6 kA at 500 V, and 11.9 kA at 690 V. Those numbers cover most industrial LV distribution — 240 V single-phase taps, 400 V three-phase common in European and Asian plants, and 480/500 V North American services. At 690 V the 11.9 kA figure is still adequate for many motor control centre applications, but you will want to verify the available fault current at the point of installation. Rated insulation voltage is 800 V, and the operating temperature range spans -25 °C to 70 °C, with storage from -40 °C to 80 °C. The front face carries IP40 protection — sufficient for a closed switchboard or MCC bucket; not rated for washdown or outdoor exposure without an additional enclosure. Maximum power loss at rated current is 80.1 W, which factors into the thermal budget for a densely packed panel.
Physical fit and panel integration
The 3VA1332-5MH32-0AA0 measures 248 mm high, 138 mm wide, and 110 mm deep — a 3-pole frame. It mounts via screw-on lugs or a DIN-rail adapter plate; the 138 mm width fits a standard MCC bucket or panel cutout.