Abstract: The following specification describes a bimetal in the limiter assembly of a circuit breaker to operate the trip crossbar for opening the main circuit breaker contacts. An arm is also provided on one blade of the current limiter contacts to also operate the trip crossbar for ensuring rapid opening of the main contacts of the circuit breaker in response to high fault currents. The bimetal is connected between the electromagnet winding and one of the current limiter contact blades in shunt with a path of selected resistance. The resistance is selected as desired by connecting pigtail conductors of desired size either in shunt with or to selected portions of the bimetal to control the current passing through the bimetal for controlling the heat of the bimetal in accordance with the rating of the breaker. A calibration assembly for the bimetal is carried by the electromagnetic assembly.

Abstract: The following specification describes a magnetic assembly for use in controlling the main contacts of a circuit breaker. The magnetic assembly includes a yoke, an armature for attraction to the yoke to move an operating lever and a pivotable adjustment arm. The lever operates the trip crossbar, which opens the main contacts and is in turn pivotably carried by the adjustment arm. One end of the operating lever is held against longitudinal movement relative the trip crossbar, when the adjustment arm is pivoted to calibrate the circuit breaker. The lever therefore pivots on the adjustment arm to move the armature towards or from the yoke to control the armature air gap without altering the lever travel distance to the crossbar. The armature is also mounted on the lever for relatively linear movement in relationship to the yoke.