Abstract: Each raceway stretch includes a base section, external walls; one or more compartment walls providing for the existence of sub-raceways, folds capping the walls and forming longitudinal slots and a cover section for each sub-raceway. The internal bottom surfaces of each base section are coplanar and have juxtaposable end cuts over the whole extension thereof. The elbow includes for each sub-raceway, an angled closing member having skirts engageable simultaneously in longitudinal slots of both raceway stretches, closing portions of a sub-raceway of each stretch; and a covering member which, in said active position, covers said angled closing members from above and is provided with means for engagement with said base sections.