What it is and what it does
The Siemens 3VM1332-5EE32-0AA0 is a 3-pole SENTRON molded case circuit breaker (MCCB) rated for line protection, with a TM220 thermal-magnetic trip unit that handles overloads and short circuits without external power. It's designed for panel-mount installation in commercial and industrial distribution boards where you need high fault-current interruption — the kind of part you spec into a main or feeder breaker position and forget about until a fault happens. The interrupting ratings tell the story: 187 kA at 240 V AC, 121 kA at 415 V and 440 V, and 76 kA at 500 V. That's serious fault-current capacity for a 320 A frame — it'll clear a bolted fault upstream of a big transformer or a service entrance without the arc flash getting worse than what the label says. The 690 V AC rated operating voltage and 800 V rated insulation voltage mean it's built for 480/277 V and 600 V systems with plenty of headroom.
Thermal derating — the real-world ampacity
At 40 °C, 45 °C, and 50 °C ambient, this breaker holds its full 320 A rating without derating. At 55 °C it drops to 313 A, at 60 °C to 306 A, at 65 °C to 299 A, and at 70 °C to 292 A. That's a gentle slope — about 1.4 % loss per 5 °C step above 50 °C — so you can run it in a warm enclosure without panic-derating the whole panel. The operating temperature range is -25 °C to 70 °C, with storage from -40 °C to 80 °C.
Panel fit and environment
Dimensions are 248 mm high, 138 mm wide, 110 mm deep — a standard MCCB footprint that fits most DIN-rail or direct-mount panel layouts. The front face carries an IP40 protection rating, meaning it's protected against tools and wires >1 mm but not against water ingress; keep it inside a panel, not on a washdown wall. Power dissipation at full load is 80 W, so factor that into your enclosure thermal calculation.