Circuit breaker components and terminals are sized to provide adequate cooling when rated circuit current flows continuously through the circuit breaker. When such circuit breakers are used within load centers and other such enclosures, consideration is given to the ambient temperature within the enclosure and its effect on the components within the circuit breaker case. Of particular interest is the effect of ambient temperature on the temperature sensing bimetal trip unit which thermally responds to overcurrent conditions through the associated electric circuit to interrupt circuit current when the bimetal becomes thermally-displaced a predetermined distance. In extreme climatic conditions, the circuit breaker may be rated at lower current values when such circuit breakers are within enclosures to compensate for the climatic conditions. A circuit breaker within an enclosure within torrid desert conditions would otherwise interrupt circuit current when normal or rated current transfers through the circuit breaker. This so-called "nuisance tripping" of circuit breakers due to ambient temperature rather than electric circuit conditions can be problematic especially when such circuit breakers protect oil drilling rigs and the like.
U.S. Pat. No. 3,801,875 describes a circuit breaker support base and compact enclosure entirely made from a plastic material. U.S. Pat. No. 4,491,897 describes a similar compact circuit breaker base which can be installed within a metal enclosure. It would be economically advantageous to combine the cost benefits derived from a unitary plastic circuit breaker support base with the thermal advantages attainable with a complete metal enclosure.
Accordingly, one purpose of the invention is to provide a unitary plastic circuit breaker support base requiring fewer component parts along with thermodynamic features that cooperate with the metal heat sink enclosure for excellent electrical response over a wide range of ambient temperature conditions.
USPTO Backgrounds
USPTO Backgrounds