An electrical switching apparatus for housing a pair of opposing circuit breakers includes a panelboard having a first longitudinal axis and configured to support the pair of opposing circuit breakers to define a gap therebetween, the gap having a second longitudinal axis extending generally parallel to the first longitudinal axis. An insulative barrier is arranged to define a plenum region having a third longitudinal axis, and is operatively disposed in the gap, wherein the third longitudinal axis extends generally parallel to said second longitudinal axis.