What this breaker carries — the ratings that matter underground
The LV839101 is a 3-pole MasterPact MTZ2 drawout breaker rated 2000 A continuous at 40 °C. That continuous rating is the number you size the bus and cable to — it's the thermal limit the frame sheds without tripping on a hot mill floor or in a packed switchgear lineup. Interrupting capacity is the real story: 200 kA Icu at 254 V and 508 V AC, and 130 kA Icu at 635 V AC, all per ANSI C37.50. That means this frame clears a bolted fault at the main lug without the arc flashing over to the next section — built for the pit where fault current is high and the gear has to hold. Short-time withstand current is 22 kA for 0.5 s (ANSI C37.50), so it coordinates downstream with feeders that need a deliberate delay before the main opens. Integral instantaneous protection is set 49.5–55.5 kA — that's the magnetic trip that catches a direct short without waiting.
Drawout mount and panel fit
Drawout mounting means the breaker racked out isolates the line and load — no need to unbolt bus when swapping a unit underground. Mounting support is base plate rails; the chassis sits on a dedicated sub-base, not cantilevered off the door. Footprint is 17.5 in wide by 17.3 in tall by 16.8 in deep. Connection pitch is 4.5 in between phases. That depth matters when the enclosure back wall has a gland plate or a rear-exit bus duct — you need the 16.8 in plus the racking clearance.
Durability for the duty cycle
Mechanical endurance is 12,500 cycles; electrical endurance under load is 2,800 cycles at rated current per ANSI C37.50. Maximum breaking time is 9 ms, and closing response is 70 ms — fast enough to limit arc energy on a motor start or a feeder fault. Rated making and breaking capacity is 50 kA — that's the close-and-latch rating for the mechanism when closing into a fault. The L1F breaking capacity code tells you the specific interrupting rating variant for this frame.