The LV839091 is a Masterpact MTZ3 40 HC automatic switch disconnector from Schneider Electric, rated for 4000 A at 40 °C in a 3-pole drawout chassis configuration. It's built for main distribution in large industrial and commercial power systems where you need a single device that can both switch and isolate the incoming feed. Breaking capacity is 200.0 kA Icu at 254 V AC and 508 V AC, and 130.0 kA Icu at 635 V AC, per ANSI C37.50 with an external relay. The short-time withstand rating is 100 kA for 1.5 seconds (ANSI C37.50), which tells you this device can ride through a delayed trip coordination window — important for selective coordination downstream where you want the feeder breaker to clear first.
This is a drawout chassis unit, so the moving portion (the breaker itself) slides in and out of a fixed cradle. That's a big deal for maintenance — you can rack the unit out for inspection or replacement without disconnecting the main power cables. It mounts on a chassis support, not a DIN rail, so plan for a dedicated cubicle or switchgear lineup. Dimensions: 31.07 in wide, 18.8 in tall, 16.8 in deep. The connection pitch is 9.06 in. That's a large footprint — make sure your enclosure or switchgear bay has the clearance, especially for the drawout travel path.