Steel Wire Power Cables Carry the Tensile Load That Tape Armour Cannot
steel wire power cables, steel wire armour SWA, BS 5467 armoured cable, riser cable tensile armour, galvanised steel wire armour
A steel wire armoured power cable exists for one duty no other sheath layer performs: carrying the cable's own weight, and the pull of its installation, in tension. Over the bedding sits a single layer of hot-dip galvanised steel wires laid in a close helix — BS 5467's prescription for multicore thermoset-insulated cable at 0.6/1 and 1.9/3.3 kV, mirrored in IEC 60502-1 construction practice. Wire count and diameter set the breaking force; heavier armour classes exist precisely so the mechanical margin scales with the route. The application list reads as a catalogue of tensile cases: vertical risers through buildings, mine shafts and steep inclines where tape armour is forbidden by load direction, submarine and river-crossing routes where the cable supports itself in water, and long duct pulls where pulling tension climbs with every bend. On a pull, the wire path carries tension the moment the cable straightens around a bend radius — which is why pulling calculations limit tension against armour capability and side pressure together, not conductor strength alone. Corrosion is a coating question. Galvanisation protects against neutral soil chemistry; acidic ground, alkaline landfill and coastal chloride demand a polyethylene oversheath over the armour or an additional barrier, because exposed steel wire rusts to section loss while rust-stained PVC hides the damage until terminations fail. Two electrical notes follow. Armour wire can serve as a protective conductor only after its metallic cross-section and low conductivity — orders of magnitude below copper — are checked with the adiabatic equation; the calculation, not convention, decides. And a single steel-wire sleeve around one AC core forms a magnetic short-circuited secondary that heats under load, which is why single-core circuits use aluminium wire armour instead: non-magnetic, and sized for the same mechanical duty. At termination, every steel wire power cable needs the armour clamped, bonded and sealed — compression glands sized for the helix, earth continuity proven, bends respected. Armour earns its weight only where tension is the design force.
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