The LV839305 is a Masterpact MTZ3 40 HB automatic switch disconnector rated 4000 A at 104 °F (40 °C) — that is the continuous current it carries without derating in a typical 40 °C ambient. For a main or tie breaker on a 4000 A bus, this is the frame size that matches the bus rating, not a derated step-down. Breaking capacity is 200 kA Icu at 240 V AC, 150 kA at 480 V, and 100 kA at 600 V per UL 489. Integral instant protection is rated 170 kA, meaning the magnetic trip element handles that level of short-circuit current without relying on the electronic trip unit alone. This is a selectivity and arc-flash coordination parameter — the breaker clears fast enough to let downstream devices ride through.
Drawout construction and panel integration
Drawout mounting means the breaker chassis stays bolted to the switchboard frame while the moving portion racks in and out. For a 4000 A main, this is the standard for maintenance isolation — you rack the breaker to the test or disconnected position without unbolting power cables. Chassis-mount support and a connection pitch of 9.06 in (230 mm) define the bus-bar centers and the cutout in the switchboard floor. Width 31.07 in, height 18.8 in, depth 16.8 in. Verify switchboard compartment depth before specifying.