The flat bus bars of the tap-off section are outwardly offset in their central portions from their closely spaced relationship in the adjoining portions. Connectors having relatively wide rectangular contact plate portions are electrically connected respectively to the centra1 portions of the bus bars in a singlebolt type joint. Each connector has a relatively narrow offcenter connecting strap portion, the free end portion of which extends perpendicularly to the contact plate portion. The lengths of the perpendicularly extending free end portions of the connecting strap portions vary according to the distances of the contact plate portions from a side of the tap-off section. In a four-pole tap-off section, two connecting strap portions are disposed at the top of the tap-off section and spaced from each other longitudinally of the tap-off section, and two connecting strap portions are disposed at the bottom of the tap-off section and spaced from each other longitudinally of the tap-off section. In a double run of parallel connected feeder bus duct sections, each connector of a tap-off section is electrically connected to a pair of corresponding bus bars connected respectively in the two runs.