Undervoltage release device for circuit breakers

Claim 1

An undervoltage release device for tripping an electric circuit breaker automatically in response to an abnormal undervoltage condition, said device comprising, in combination: A. a frame for mounting attachment to a circuit breaker; B. a trip member mounted by said frame for movement between a latched position and a circuit breaker tripping position, said trip member being spring-biased to said tripping position; C. a solenoid mounted by said frame, said solenoid having 1. a plunger movable between a seated position and an extended position, and 2. a coil for developing a magnetic force sustaining said plunger in its seated position under normal line voltage conditions; D. a latch member linked to said plunger and mounted by said frame for movement from a first position latching said trip member in its latched position and a second position in response to movement of said plunger from its seated position to its extended position, thereby releasing said trip member for movement to its tripping position; E. a first spring calibrated to overpower the magnetic force of said solenoid in the event of an abnormal undervoltage condition such as to move said plunger to its extended position and said latch member to its second position; F. a reset member mounted by said frame for movement from a normal position to a reset position; G. a second spring positioned to be charged by movement of said reset lever to its reset position, said charged second spring biasing said plunger to its seated position; and H. means carried by said trip and latch members for inhibiting movement of said plunger to its seated position under the bias of said second spring until said trip member is fully returned from its tripping position to its latched position, whereupon said second spring abruptly discharges to snap said plunger to its seated position and said latch member to its first position.