3VM1332-4EE32-0AA0 SENTRON MCCB, 320 A, 3-pole, TM220 releas

It's rated 320 A continuous at 40 °C (same at 45 °C and 50 °C, so you get full ampacity through typical enclosure ambient temps), then derates to 292 A at 70 °C. That's the number you care about for a hot panel in summer — the breaker doesn't force a derate until you're past 50 °C. Interrupting capacity is 121 kA at 240 V AC and 76 kA at 415 V AC — that's a high-fault rating for a 320 A frame, meaning it can handle a dead short on a transformer secondary or a large motor bank without the arc flash escalating upstream. The TM220 thermal-magnetic release gives a fixed thermal curve and magnetic trip, no electronics to fail, no adjustment knobs to walk off. Insulation voltage is 800 V, operating voltage 690 V AC, so it's comfortable on 480/277 V and 600 V systems with headroom. It's a straightforward thermal-magnetic main breaker: mount it, land the lugs, and it protects.