F·01Manufacturers, EPCs and utilities
Inside a subsea power cable
Conductor, insulation, sheath, jacket and armour: what each layer of a high-voltage subsea power cable does and what a buyer should check before buying.
A high-voltage subsea cable looks like a black pipe. Inside, it is built in layers, each with a precise job. Understanding them helps you specify well, review a bid and talk to the manufacturer. On our home page you can strip one, layer by layer.
From the inside out
Conductor
Copper or aluminium. In large cross-sections it is made segmented, in sectors separated from each other, to reduce the losses caused by alternating current. This is where the power flows.
Conductor screen
A semiconducting layer that smooths the electric field over the conductor’s surface.
Insulation
In modern AC cables, cross-linked polyethylene (XLPE). Its thickness grows with the voltage. Some DC links still use mass-impregnated paper.
Insulation screen and water blocking
Another semiconducting layer, plus tapes that swell with moisture to stop water travelling along the cable if it is damaged.
Metallic sheath
In subsea cables it is usually a lead alloy: the radial water barrier, which also carries fault current.
Jacket
Polyethylene that protects the sheath from corrosion and abrasion.
Armour
Metal wires that carry the mechanical tension of laying and protect the cable on the seabed. Three-core cables usually use galvanized steel; single-core AC cables use non-magnetic materials to limit losses. An outer yarn serving goes on top.
In a three-core cable, the three cores sit together inside the same armour, often with fibre optics in the gaps for communications and monitoring.
Why it matters to the buyer
- Armour depends on the route. Depth, currents, fishing and anchors decide how much protection is needed and whether the cable is buried.
- Joints and terminations are critical points. Specify and test them with the same care as the cable.
- Tests are documented. Factory, acceptance and after-lay: each with its protocol.
- Repairs are planned in advance. How much spare cable, where it is stored and who joins it.
What is coming in Panama
The largest subsea crossing in sight is the interconnection with Colombia: 500 kilometres, 120 of them subsea, with an estimated investment of USD 800 million, if it goes ahead (La Prensa, 2025-09-13).
