Abstract: A sealed lay-in electrical conduit duct which is oil-tight and is comprised of U-shaped sealing collars which telescope into adjacent ends of aligned open ended sheet metal duct sections which are troughs generally U-shaped in cross-section and have their open sides unobstructed throughout their length and closable by a movable sealing trough cover. The sealing collars and duct sections have telescoping bottom and side wall portions, each of which carries elongated cooperating interengaging rib and groove elements which are aligned and extend normally to the longitudinal axis of the duct sections. Each collar member carries a sealing element extending throughout substantially its entire length which covers and seals the line of juncture of the adjacent ends of trough sections held in rigid aligned relation by the collar member.