The LV839077 is a MasterPact MTZ3 drawout air circuit breaker, 3-pole, rated 4000 A continuous at 40 °C. It ships without a Micrologic trip unit — the buyer selects the protection relay separately. The frame carries an breaking capacity code, which means 200 kA Icu at 254 V AC 60 Hz per ANSI C37.50, 150 kA at 508 V, and 100 kA at 635 V. That is the fault-clearing ceiling; the actual interrupting rating depends on the installed trip unit and system voltage. This is a main or large-feeder breaker for ANSI-style switchgear — not a panelboard or MCC bucket device. The drawout cradle lets you rack the breaker between connected, test, and disconnected positions without pulling cables, which is standard for maintenance and arc-flash mitigation in industrial and data-center distribution.
The 100 kA Icw for 0.5 s (ANSI C37.50) is the short-time withstand — the breaker can carry 100 kA symmetrical for half a second while downstream breakers clear a fault. That is the number that governs selective coordination: if your upstream transformer or generator can deliver 100 kA, this frame holds long enough for the feeder breaker to open. The integral instantaneous protection is set at 243–297 kA, which is an arc-flash mitigation band — it clears bolted faults in under 9 ms (the listed maximum break time) before the short-time delay expires. Mechanical endurance is 10,000 cycles, electrical endurance 1,000 cycles under rated load per ANSI C37.50. For a main breaker that operates a few times a year, that is effectively life-of-installation. For a generator or process breaker that cycles weekly, track the count.