Abstract: An expandable raceway for electrical wiring is constructed of a main section which defines a main passage. In cross-section the main section includes a leg and parallel arms that extend in the same direction from opposite ends of the leg. Each arm is provided with an indexing formation to receive a cooperating indexing formation along the free edge of an arm of an L-shaped auxiliary section for mounting the auxiliary section to the main section without dismounting from a surface to which it is already affixed or dismantling the main section. In cooperation with one arm of the main section, the auxiliary section defines an auxiliary passage outside of the main passage. The auxiliary section includes one arm parallel to the arms of the main section and one arm coplanar with the base of the main section and the latter arm includes the indexing formation thereon covers over the open sides of the sections.