MasterPact MTZ2 — the 1000 A fixed breaker for main switchboard duty
The Schneider Electric LV846551 is a MasterPact MTZ2 fixed circuit breaker, 4 poles, rated 1000 A at 40 °C. It carries an H10 performance class: 50 kA rated service breaking capacity (Ics) at 1150 V AC 50/60 Hz, with a rated short-circuit making capacity (Icm) of 105 kA at the same voltage. That 50 kA Ics at 1150 V means it clears a fault at full rated voltage without needing to trip upstream — the breaker itself handles the interruption, so downstream coordination holds. This is a Category B breaker, which means it is designed for selectivity in distribution — it withstands a short-time current (Icw) of 50 kA for up to 3 seconds, allowing downstream devices to clear a fault first before this unit trips. That 3-second withstand window is what makes selective coordination practical in a main or tie breaker position. Mounting is fixed on rails or a base plate, with rear connections both upside and downside — typical for switchboard builders who want bus-bar stabs rather than cable lugs. The 115 mm connection pitch matches standard MasterPact MTZ bus-bar spacing.
Rated operational voltage (Ue) is 1150 V AC 50/60 Hz, with an insulation voltage (Ui) of 1250 V AC and impulse withstand (Uimp) of 12 kV. If the switchboard ambient runs hotter (say 50 °C), expect a derating curve — typical MasterPact MTZ2 guidance is to reduce by about 1% per degree above 40 °C. The sensor rating range of 400 A, 630 A, 800 A, and 1000 A means the breaker can be re-rated by swapping the electronic trip unit sensor, not the entire frame. Mechanical durability is 25,000 cycles with periodic preventive maintenance; electrical durability is 500 cycles at 1150 V AC. For a main breaker that operates a few times a year, that electrical endurance is effectively life-of-installation. For a breaker that sees frequent switching (e.g., capacitor bank or generator coupling), the 500-cycle figure is a real limit — plan for a contact inspection or replacement at that interval.
Lifecycle and sourcing — active, but plan ahead
For a critical-spare holding or a new switchboard project, it is worth getting a quote locked in early — the 1000 A H10 variant is a common spec, but lead times can stretch when global demand for MTZ2 frames is high.
Physical integration — what fits where
IP30 protection is standard for enclosed switchgear. Altitude derating starts above 2000 m. The neutral position is left — important when phasing bus-bar runs in a 4-pole switchboard. Control is via push-button and the breaker ships without a control unit, meaning the electronic trip unit (Micrologic X or similar) is ordered separately. Factor that into your BOM: the LV846551 is the frame and mechanism only.