The design of PN series molded case circuit breaker (hereinafter circuit breaker)indicates the newest current-limiting principle and manufacturing technology with the characteristics of compact structure, modulization,high breaking capacity, no flashover. It is used for infrequent exchange and startup of motor in the circuit AC50HZ of which rated insulation voltage is 750V，rated working voltage 690V or less, rated working current upto 1600A. Cirucit Breaker has the overload, short-circuit, and undervoltage protection device, which can protectthe circuit and power-supply device from damages. Circuit Breaker can be devided into N,S,H type.This circuit breaker can be installed vertically ( Erect), and horizontally installed( Level). The line of this circuit breakercan not be connected reversely, that is, 1,3,5 line connected to power line, 2,4,6 connected to the load line.This circuit breaker has isolation function, using the mark to refer to.