Current limiting circuit interruption devices such as molded case circuit breakers, generally employ a movable contact arm which is electrodynamically repulsed upon the occurrence of a short circuit overcurrent condition to drive the attached movable contact away from the fixed contact and rapidly disconnect the protected circuit. The same movable contact arm cooperates with an operating mechanism to separate the movable contact upon occurrence of overcurrent conditions less than short circuit intensity. In most current limiting circuit breaker designs, a flexible braid conductor is attached both to the movable contact arm and to the load terminal strap to insure good electrical continuity between the movable contact arm and the load terminal strap during such intense short circuit interruption.
U.S. Pat. No. 4,733,033, which Patent is incorporated herein for reference purposes, describes one such current limiting circuit breaker that utilizes a spring-clip contact arm retainer to insure good electrical continuity between the movable contact arm and the associated support structure.
U.S. Pat. No. 4,245,203 describes a movable contact arm arrangement wherein the contact arm support posts are bifurcated. The current paths through the bifurcated support posts generate complementary magnetic fields which, in turn, drive the support posts into good electrical connection with the movable contact arm pivot during intense short circuit conditions.
U.S. Pat. application Ser. No. 330,521, filed Mar. 30, 1989, now U.S. Pat. No. 5,004,878, entitled "Molded Case Circuit Breaker Movable Contact Arm Arrangement" describes a movable contact arm arrangement employing contact springs to increase the tension between the fixed and movable contacts under quiescent current operating conditions while contributing to prevent contact arm rebound during overcurrent conditions. This application is incorporated herein for purposes of reference and should be reviewed as indicative of the advanced state of the art of current limiting contact arm assemblies.
When the movable contact arm and the movable contact arm support base described within aforementioned U.S. Pat. No. 5,004,878 are attached to the circuit breaker case, it is important to maintain close tolerances between the sidewall surfaces of the circuit breaker case and the edges of the movable contact arms to insure maximum tension between the fixed and movable contacts and hence decrease the operating temperatures of the contacts during long periods of continuous operation under quiescent operating conditions.
One purpose of the invention accordingly, is to provide automatic means for accurately positioning the movable contact arm and movable contact arm support base within the circuit breaker case while at the same time compensating for any manufacturing tolerances that are accumulated between the contact arm support base and the circuit breaker case.
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USPTO Backgrounds