In low-voltage distribution backbone networks, the 400 A current rating shoulders the heavy responsibility of conveying electric power from transformer outlets to large sub-distribution circuits, acting as the core lever for the stability of the entire power supply system. The OFA-M1 series 400 A molded case circuit breaker (model OFAM1-400/3300), with a frame rated current of 400 A, inherits the series’ consistent high breaking and high insulation performance. It features a rated ultimate short-circuit breaking capacity of 35 kA, an insulation voltage of 690 V, and an impulse withstand voltage of 6 kV. With powerful and robust electromechanical characteristics, it provides reliable protection for the incoming supply and high-capacity feeders in industrial main distribution, commercial complexes and critical infrastructure. The product strictly complies with the national standard GB/T 14048.2 and is an indispensable backbone protective component in medium and large-scale low-voltage distribution solutions.