The LV839059 is a Schneider Electric Masterpact MTZ3 40 HF automatic switch disconnector. It's a 4000 A drawout unit, 4-pole, built for distribution duty.
Rated 4000 A at 104 °F (40 °C) ambient. That's the continuous current it carries without derating — if your switchgear room runs hotter, you'll need to apply the manufacturer's temperature correction. Short-time withstand (Icw) is 85 kA for 1.5 s per ANSI C37.50, which covers the coordination window for downstream breakers to clear. The drawout chassis lets you rack the unit out for maintenance without pulling the main bus.