How power cables are made

Edison's first cables of 1882 were copper rods wrapped in jute, in pipes filled with a bituminous compound.

stations: 9
things upstream: 26
raw sources: 10
steps from the ground: 6

The short version

Copper is drawn through diamond dies into thin wires, and many wires are stranded into a flexible conductor. An extruder melts plastic granules and forms a layer around the strand, which is cooled in a water bath. Insulated cores are twisted together into a bundle, sometimes braided in tinned copper, and sheathed by a second extrusion. Each length is printed, then tested at high voltage in a Faraday cage.

Draw the copper

Copper is pulled through diamond dies on drawing machines until it is thin wire. The wire gets longer and finer with each die.

Goes in
Copper wire
Strand the conductor

Fine wires are twisted into a strand. The class of strand chosen here sets how flexible the finished cable will be.
Extrude the insulation

Plastic and color granules feed from hoppers into a heated screw that melts them. In the head, the melt forms around the passing copper strand.

up to 240 °C, in some cases 300 °C

Goes in
Polyethylene
Cool in water

The insulated wire runs through a water bath until it is cool to the core, so turns do not stick together on the drum.
Strand the cores

Colored or numbered cores feed into a stranding machine in set sequence, and rotary motion brings them together into a kind of cord. Stuttgart's tube strander is 50 m long.
Braid the shield

Servo and control cables get an inner jacket and then a tinned copper braid against electrical interference and mechanical load. The braid covers 80 to 85 % of the surface.

Goes in
Copper wire
Extrude the outer sheath

A second extruder lays on the protective plastic sheath, with a fleece winding underneath so it does not stick to the core.

Goes in
PVC
Print the legend

Type, specifications and traceability marks are printed along the sheath as it passes.
Test at high voltage

In a Faraday cage, simulated short circuits at up to 6,000 V check insulation between wires and against the shield. Passed cable is rewound onto wooden reels.

End of the linePower cable

Worth repeating

Thomas Edison's first power distribution system in 1882 in New York City used copper rods wrapped in jute and placed in rigid pipes filled with a bituminous compound.
Mass-impregnated paper-insulated medium-voltage cables were commercially practical by 1895.
Armored cable, known as BX, was introduced in 1906 with a flexible steel sheath around rubber-insulated conductors.