Abstract: An electric conductor incorporates at least one optical fibre and has a central axial element with at least one layer of elements helically stranded about it. At least one of the elements, preferably the central axial one, includes at least one optical fibre which is enclosed in a longitudinally extending welded metal tube (typically stainless steel). A second metal tube of greater thickness and higher conductivity than the welded metal tube and having an unwelded longitudinal seam surrounds the welded tube. The second tube is typically of aluminium and served to increase the diameter of the element so that a greater range of useful conductor sizes can be formed by using it in conjunction with appropriately chosen wire diameters.