Circuit breaker comprising a current transformer with a partial air gap

The present invention relates to current transformers and, more specifically, to current transformers for use in circuit breakers. A circuit breaker assembly having an electronic trip unit used to detect an overcurrent condition in a protected electrical circuit. The electronic trip unit being electrically connected to a current transformer used to sense electrical current and provide operating power to the electronic trip unit. The current transformer comprising a metal core having a top surface and a bottom surface where the difference between the top and bottom surfaces defines a height of the core. The core having a concentrical opening extending through the height so that the distance between an outside point on the concentrical opening and the closest outside point of the core defines a thickness of the core at that point. Passing through the core opening is a primary winding and encircling the thickness of the core is a secondary winding. To optimize usage of the current transformer, a partial air gap is added to the metal core so that the range of operation is maximized while at the same time minimizing the remanence attenuation.