What this MasterPact MTZ3 brings to a switchboard
The LV839300 is a MasterPact MTZ3 50 H drawout circuit breaker from Schneider Electric, rated for 5000 A continuous at 104 °F (40 °C) on a 3-pole configuration. It's built for UL 489 applications up to 600 VAC, with an H breaking capacity code — meaning it delivers 100 kA Icu at 240 VAC, 100 kA Icu at 480 VAC, and 85 kA Icu at 600 VAC, all per UL 489. The drawout cradle lets you rack the breaker out for maintenance or replacement without pulling the whole enclosure apart — a real time-saver when you're working a line-down window.
Short-time withstand and coordination headroom
One spec that matters for selectivity studies is the rated short-time withstand current (Icw): 85 kA for 0.5 seconds per UL 489. That means the breaker can carry 85 kA through its main contacts for half a second without welding or damage, which gives downstream breakers time to clear a fault before this one trips. For a site electrical engineer working a coordination study, that 85 kA Icw figure is the number that decides whether you can use this as a main with smaller feeders downstream, or whether you need a higher-rated frame.
The breaker measures 31.07 in wide by 18.8 in high by 16.8 in deep (789.1 x 478.1 x 426.8 mm). The drawout mounting sits on a base plate with rails, and the connection pitch is 9.06 in (230 mm) between phases. That's a big footprint — plan your enclosure depth and door swing accordingly. The 5000 A rating also means you're looking at serious buswork; the lugs or bus connections need to handle that continuous current without derating.
Protection and durability specs
This breaker comes without a Micrologic trip unit — you need to specify and install the trip unit separately based on your protection curve requirements. The integral instantaneous protection is set at 153...187 kA, which is the magnetic-only trip level for bolted faults. Mechanical durability is rated at 5000 cycles per ANSI C37.50, electrical durability at 1000 cycles under the same standard. Maximum breaking time is 25...30 ms, and the maximum closing response time is 70 ms. The rated breaking and making capacity is 90 kA. That's solid for a main breaker that might see only a handful of operations per year but needs to clear a fault when it happens.