The LV839311 is a MasterPact MTZ3 drawout circuit breaker rated for 4000 A continuous at 40 °C (104 °F). That 4000 A figure is the line-rated current — the breaker carries that load continuously without exceeding its thermal limits, per the datasheet. The H3 breaking capacity code means 100 kA Icu at 254 V and 508 V AC, 50/60 Hz per ANSI C37.50, and 85 kA Icu at 635 V. This is a 3-pole (3P) unit in drawout mount, meaning it slides into a cradle in the switchgear lineup — no hard wiring to the breaker itself, so you can rack it out for maintenance or replacement without de-energizing the bus. The drawout chassis mounts on base plate rails with a connection pitch of 9.06 in (230 mm). Note: the breaker ships without a Micrologic trip unit (per the description). That trip unit is ordered separately and plugs into the front — the breaker is just the power frame and ArcBlok arc chute. If you're replacing an existing MTZ3 frame, verify the trip unit model from your BOM.
Integration into the switchgear lineup
The breaker's short-time withstand rating (Icw) is 85 kA for 0.5 s per ANSI C37.50 — that's the current the breaker can carry for half a second while a downstream device clears a fault, without the breaker itself tripping or welding. That figure drives selective coordination: if your upstream transformer or feeder can deliver 85 kA for 0.5 s, this breaker holds in. Mechanical durability is 12,500 cycles; electrical durability is 2,800 cycles under ANSI C37.50 test conditions. For a main breaker that sees infrequent switching (maybe a few operations per year), that's essentially a lifetime mechanical rating. The 25–30 ms maximum breaking time and 70 ms maximum closing response time are the mechanical travel times — the actual arc extinction happens faster with ArcBlok.
Protection and application context
The device application is protection — this is a circuit breaker, not a disconnect switch. The integral instantaneous protection range is 171–209 kA, which is the magnetic trip threshold for the breaker frame itself (not the Micrologic trip unit, which is ordered separately). That range means the breaker's internal instantaneous element will clear faults above 171 kA without waiting for the trip unit. For a 4000 A main on a large industrial or data-center switchboard, that 170 kA figure is the ceiling for your available fault current study. The CT rating matches the line current at 4000 A.