Two ways to armour a cable
An armoured power cable has the same core as an unarmoured one: conductors, insulation, fillers and a binder. Over that sits an inner sheath, also called bedding, then a metal armour layer, then the outer sheath. The armour is what changes the cable's mechanical behaviour, and it comes in two common forms for multicore low voltage cable.
Steel wire armour (SWA) is a layer of galvanised steel wires laid helically around the bedding. Steel tape armour (STA) is usually two steel tapes wound over the bedding with overlapping gaps, so that the second tape covers the gaps in the first. Both forms are permitted in IEC 60502-1. In Chinese designations, YJV22 denotes copper, XLPE, PVC and steel tape armour; SWA versions use a different code, and the desk always writes the full construction on the spec sheet rather than relying on the code alone.
Reference construction and comparison
The partner plant catalogue behind our armoured cables page covers steel tape armour. Its reference model is a 0.6/1 kV Cu/XLPE/PVC/STA/PVC 4x35 mm2 cable with 0.9 mm XLPE insulation, a 1.2 mm PVC inner sheath, 0.2 mm steel tape, a 1.8 mm outer sheath, an overall diameter of about 30 mm and a weight of about 2,067 kg per kilometre. SWA constructions to BS 5467 (PVC) or BS 6724 (LSZH) are matched to plants that specialise in them.
| Aspect | Steel wire armour (SWA) | Steel tape armour (STA) |
|---|---|---|
| Form | Galvanised steel wires laid helically | Steel tapes wound with overlap |
| Main protection | Crushing and impact, plus some tensile strength | Crushing and impact; little tensile strength |
| Pulling and vertical runs | Better suited; wires carry part of the load | Not for heavy pulling or long vertical drops |
| Flexibility | Moderate; bending radius per standard or datasheet | Stiffer in some sizes; per datasheet |
| Typical markets | UK-style specifications (BS 5467, BS 6724) and many export projects | Chinese catalogues (YJV22 type) and IEC 60502-1 projects |
| Use as protective conductor | Often considered by the designer; armour resistance must be verified | Rarely relied on; designer's decision |
| Reference source on this site | Matched plant, per datasheet | Partner plant catalogue, 4x35 mm2, OD approx. 30 mm |
Where each one fits
STA is a good fit for direct burial and fixed installation where the cable is laid into a trench rather than pulled a long way. The tape resists crushing from backfill and impact from tools. It can withstand external mechanical forces, but it is not designed to carry a large tensile load, so long pulls through ducts or vertical drops in shafts are better served by wire armour.
SWA is the default armoured cable in UK-influenced markets and in many project specifications in the Middle East and Africa. The wires add tensile strength, so the cable copes better with pulling, with vertical runs and with ground movement. On cable trays outdoors and in industrial plants, SWA is also the form that most gland systems and site electricians expect. If the drawings or the client's standard say BS 5467 or BS 6724, the armour is steel wire by definition.
For single-core cables in AC circuits, neither steel option is normally used: steel around a single conductor carrying alternating current heats up through induced currents. Single-core cables use aluminium wire armour instead, explained in the AWA armour article.
Armour, earthing and glands
Armour is a continuous metal path along the cable, so it is bonded to earth at the gland. Whether the armour may also serve as the circuit protective conductor is a design decision under BS 7671 or the local wiring rules, and it depends on the armour's resistance compared with the phase conductor. That is one reason the armour itself must be checked. BASEC has warned about SWA cable whose effective conductor cross-section was up to two sizes smaller than marked, with conductor and armour resistance both out of specification. A cable like that may look correct from the outside and still fail the designer's assumptions. The undersized conductor article covers how that happens.
Gland size follows the bedding diameter and overall diameter of the cable, so the final dimensions on the spec sheet should be shared with the installer before the order is confirmed. Mixing an STA cable with glands intended for SWA is a common site problem.
Comparing armoured cable quotes
Armoured cable quotes are harder to compare than plain power cable quotes, because there are more layers where a supplier can save material. Two offers for '4x35 armoured' can differ in conductor resistance, insulation thickness, bedding thickness, armour wire diameter or tape thickness, and outer sheath thickness, and each of those changes the price per metre. The weight per kilometre is a quick first check: a cable that is much lighter than the reference construction for the same size and armour type usually has less copper, less steel or thinner sheaths somewhere.
The desk compares armoured offers layer by layer against the standard the client named, and asks each plant for the same documents: conductor resistance records per drum, dimensional checks on a sample, and armour resistance where earthing depends on it. Only then does price per metre become meaningful. Steel price also moves separately from copper, so an armoured quote can change at renewal even when copper is flat; quote validity is stated on each quotation.
What to put on the order
- Armour type: SWA, STA or AWA, and the standard (IEC 60502-1, BS 5467, BS 6724 or the national equivalent).
- Sheath materials: PVC or LSZH for bedding and outer sheath, and any flame-retardant requirement per test report.
- Dimensions: nominal armour wire diameter or tape thickness per the standard, plus overall diameter for gland selection.
- Tests: conductor resistance per drum, and armour resistance where the armour will be used for earthing.
- Drums: drum length and drum type; armoured cable is heavy, so drum size sets how much fits per drum. See packaging and drums.
Typical MOQ for armoured cable is around 500 m per size from many plants, confirmed in writing for each order; details are on the MOQ and lead time page. Send your cable schedule through the quote form and the desk will confirm which armour route each line needs.