Arc chute for an electric cuircuit breaker

Claim 1

An electric circuit breaker comprising an arc chute into which an arc is adapted to be driven for the purpose of extinguishing the arc, said arc chute comprising: a. a pair of spaced-apart sidewalls of a first insulating material extending along the length of said arc; b. a pair of conductive arc runners spaced apart within said chute for defining paths along which the terminals of said arc travel as the arc is driven into said chute; c. said runners having refractory metal surfaces along a major portion of the paths traveled by said arc terminals during circuit interruption; d. a pair of face plates of low-gas-evolving insulating material positioned on opposite sides of one of said runners between said runners and said insulating sidewalls, said plates being of a second insulating material that has a much greater surface resistivity under humid conditions than the material of said insulating sidewalls; e. said second insulating material containing one or more low ionization potential metallic components that will vaporize at temperatures produced at the surface of said plates by arcs on said one runner carrying high currents within the current interrupting rating of said circuit breaker, assuming said plate surface was bare; and f. and means for shielding the surfaces of said plates adjacent said one runner from said arcs comprising a thermally sprayed coating of refractory ceramic insulating material on said plate surfaces.