A power busway interposer enables a power busway assembly of energized busway segments to be extended, via coupling additional busway segments to the assembly, while maintaining energization of the assembly. As a result, a power busway assembly providing power support to electrical loads can be extended while maintaining power support to the electrical loads. The interposer includes separate sets of connectors that couple with separate busway segments and a switching device which selectively electrically couples the connectors, so that a power busway connector can be de-energized while another separate power busway connector is coupled to an energized busway segment and then subsequently energized. Extending the power busway assembly can include coupling separate sets of connectors to separate busway segments, where the separate sets of connectors are electrically isolated, and adjusting the switching device to electrically couple the separate sets of connectors, so that power is distributed between coupled busway segments.