an improved metal - clad gas - type high - power circuit - breaker construction is provided involving two upstanding circuit - breaker assemblages electrically interconnected adjacent their upper ends , and connected into the series line transmission circuit , preferably , adjacent the mid - portions thereof to pressurized laterally - extending power - transmission lines . improved structure is provided for simultaneously supporting the interrupting modules , or units up in the air interiorly of an outer grounded metallic casing structure , and , additionally , providing a high - pressure gas - conduit path to the pressurized insulating casing structure surrounding the circuit - breaker modules , and spaced inwardly from the outer grounded metallic casing structure . improved means are provided for increasing the electrical power capable of being interrupted by such a structure , when desired , involving a series closing resistance , which is inserted into the circuit only during the closing operation of the interrupter . during the opening operation , the resistor is kept out of the electrical circuit and is not utilized . the invention is also applicable when high - voltage surges are not contemplated by utilizing a different type of circuit - interrupter unit within each interrupting assemblage , namely , for example , a single - break circuit - interrupter unit , involving only a separable pair of contacts and gas flow passing through one or both of said separable contacts , depending upon the rating of the breaker , to extinguish the arc . the invention moreover contemplates the arrangement of a pair of circuit - breaker assemblages disposed in generally - horizontal relationship , again the two circit - breaker assemblages constituting a single pole - unit , or one phase of a three - phase circuit - breaker structure . in such a horizontally - mounted arrangement , wherein instead of the two circuit - breaker assemblages extending up in the air , in this alternate embodiment of the invention , they are disposed relatively horizontally , with the connections again being made by , preferably , pressurized conductors , and , for example , the mechanism and gas - compressor equipment housing extending lengthwise , generally horizontally along one of the horizontally - arranged circuit - breaker assemblages of the structure .