3 pole thermal overload bkn circuit breaker mcb is used in lighting distribution system or motor distribution system for protection overload and short-circuit in the system. It has high breaking capacity, can trip quickly, and its case and items are adopted by high fire-resistant and shockproof plastics. The product, with long life, is mainly used in AC 50Hz/60Hz single pole 230V or two, three, four poles 400V circuit for overload and short-circuit protection as well as for infrequent on and off switching electric equipment and lighting circuit in normal case.