It carries a MicroLogic 1.3 M electronic trip unit — the 'M' suffix means it is calibrated for motor-starting inrush and overload curves, not just distribution. The 320 A rating holds at 65 °C, so you are not forced to derate in a warm enclosure. That is the same class as the old NS400b, but in a frame that fits a 140 mm-wide backplate mount. At 690 V it still interrupts 45 kA. For a motor starter fed off a large transformer or a weak grid with high fault current, this breaker gives you the headroom to avoid cascading upstream. It is rated Category A (no intentional short-time delay) and suitable for isolation per EN/IEC 60947-2 — so you can lock it out as a disconnecting means.
Backplate mount, 140 mm wide, 255 mm tall, 110 mm deep. Horizontal or vertical orientation, flat on the back. Front connections top and bottom — no rear-access bus work required. Six accessory slots for shunt trips, aux contacts, or motor operators. The IK07 impact rating and IP40 enclosure mean it handles the bumps and dust of a typical motor control center.
Electrical durability and real-world cycling
Mechanical endurance is 15,000 cycles; electrical endurance is 12,000 cycles at 440 V at half rated current, 6,000 cycles at full rated current. For a motor-starting application that cycles a few times per shift, that is years of service.