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.