The Schneider Electric A9N19863 is a 4-pole Acti9 C120L miniature circuit breaker rated 125 A at 30 °C with a D curve. That D-curve magnetic trip — 10 to 14 × In per GB/T 10963.1, or 12 × In ±20 % per GB/T 14048.2 — means it holds through motor inrush and high-starting-current loads without nuisance tripping.
Clip-on mounting to DIN rail, 12 module pitches wide (9 mm each — 108 mm total). The tunnel terminals accept 1 to 50 mm² rigid or 1.5 to 35 mm² flexible, with a tightening torque of 3.5 N·m. Strip 14 mm of insulation. That 4-pole footprint fits a standard panel layout; watch the fill factor if you're packing multiple high-current breakers — 125 A continuous through each pole generates heat that needs breathing room inside the enclosure.
Rated operational voltage 400 V AC, insulation voltage 500 V AC, impulse withstand 6 kV. Electrical endurance 5000 cycles, mechanical 20,000 cycles. Suitability for isolation is marked — the toggle and contact-position indicator give visible break confirmation. Thermal-magnetic trip technology covers both overload (thermal bimetal) and short-circuit (solenoid) protection in one unit.