The LV839058 is a Masterpact MTZ3 40 HF automatic switch disconnector rated 4000 A at 104 °F (40 °C) — that is the continuous current it carries without derating, so for a 4000 A bus or feeder this is the frame size. The 100 kA Icu at 254 V AC (with external relay, per ANSI C37.50) tells you it can interrupt a fault up to that level without failing; the 85 kA Icw for 1.5 s is the short-time withstand, which governs selectivity coordination with downstream breakers. Four poles, fixed mount, push-button control. This is a distribution-class device, not a motor-protection breaker — it goes on the main or tie bus.
Fixed mounting means the breaker bolts directly to a mounting plate or bus structure — no draw-out cradle. The 39.2 in (996.3 mm) width and 13.9 in (352.2 mm) height define the cutout and clearance envelope; depth is 11.7 in (297.1 mm) including the push-button operator. Connection pitch is 9.06 in (230 mm) between phase centers, which matches standard bus-bar spacing for 4000 A switchgear. Plan for front-access cable or bus connections; the fixed chassis does not slide out for maintenance.