Manufacture of mineral insulated cables

A process for the manufacture of mineral insulated electric cable which comprises continuously forming a sheath from travelling metal strip, by bending the strip into tubular form and seam welding the abutting edges of the bent strip together, while the said edges and travelling along a predetermined path, and simultaneously introducing powdered insulating material and at least one conductor wire into the sheath so formed, and then passing the resulting assembly through a series of reduction means to compact the insulant powder and to reduce the diameter of the sheath, each reduction step being followed by annealing and quenching, wherein a said conductor wire is introduced into the sheath by being passed through a guide tube extending into the sheath to a point beyond the region in which said welding is effected, which guide tube has an aperture in its wall located adjacent to the path of travel of the said edges in the said region, and wherein the assembly of said conductor wire and guide tube and the insulant powder is so arranged within the bent sheath-forming metal strip that the powder is excluded from the said welding region and that the said conductor wire is directly exposed, through said aperture, to heat generated by the welding operation.