Selection Guide · 9 min read · Updated 2026-10-12
How to Select Armoured Power Cable: Steel Tape vs Steel Wire
Armour is not a general-purpose upgrade. It is a mechanical layer chosen to resist one specific family of loads - crushing, impact, or tension - and choosing the wrong type either wastes money or fails on site. This article sets out what steel tape and steel wire each resist, where single-core cables break the rule, and the sequence of questions that produces the right code.
What the armour layer actually does
Between the laid-up cores and the outer sheath there is a metallic layer whose job is mechanical. Galvanised steel tape or galvanised steel wires sit over a bedding of extruded or lapped material, and they take the abuse that would otherwise reach the insulation. What they protect against is specific, and the two types are not interchangeable.
The armour also does things people forget. It carries earth fault current if it is sized for it, it resists rodent attack and impact from tools during backfill, and it lets the cable be installed with a smaller bending radius than an unarmoured cable of the same size. What it does not do is make the cable waterproof, or allow it to be hung, or substitute for a duct where a duct is required. Water can still migrate along the inside of the cable; if the route is permanently wet, specify a water-blocking construction as well.
- Steel tape resists crushing and lateral pressure: backfill, compaction, vehicle loading above a trench, impact
- Steel wire resists axial tensile load: vertical drops, long pulls, unsupported spans, sloping shafts
- Neither type makes the cable watertight; water blocking is a separate construction feature
- Armour reduces the minimum bending radius to about 12 × overall diameter, against about 15 × for unarmoured multicore cable
- Armour must be earthed at both ends if it is used as a protective conductor, and bonded at the glands in any case
Steel tape armour: the burial default
YJV22 is XLPE insulated, with a double layer of galvanised steel tape applied helically with a gap between turns, and a PVC outer sheath. The two tapes are applied in opposite directions so that the gap in one layer is covered by the other. That geometry is good at spreading a point load around the circumference, which is exactly what happens when a stone presses on a buried cable or when a spade strikes it. It is also light and easy to strip for jointing, which is why it is the default for direct burial and for indoor routes where mechanical damage is possible.
It does almost nothing for tension: pull a tape-armoured cable and the tapes simply open up. That single fact is the whole basis of the YJV22 versus YJV32 decision, and it is worth stating plainly because the two cables look almost identical from outside.
| Application | Why steel tape is the right choice | Comment |
|---|---|---|
| Direct burial in a trench | Resists crushing from backfill and stones, impact from digging | Most common armoured cable by volume |
| Industrial floor and outdoor yard routes | Handles vehicle wheel loading and impact | Use a duct under roads carrying heavy traffic |
| Indoor routes with mechanical risk | Protects against knocks in plant rooms and risers | Tape armour is lighter and easier to support than wire |
| Cable in concrete or screed | Withstands the pressure of wet concrete and vibration during pouring | Confirm the sheath compound resists the alkalinity |
| Riser with a short vertical climb | Adequate up to roughly the length where the cable weight is carried by cleats | Above that, move to steel wire armour |
Steel wire armour: when the cable is loaded in tension
YJV32 uses a single layer of galvanised steel wires laid helically over the bedding, which turns the cable into something that can carry its own weight under tension. This is the cable for vertical shafts, mine and tunnel applications, long unsupported runs between supports, steeply sloping routes, and anywhere the cable will be pulled hard during installation. Fine steel wire, the 3 code, is the common form; thick steel wire, the 4 code, is used where the tensile demand is higher, typically for submarine or river crossings and deep vertical shafts. Wire armour is also considerably heavier and stiffer than tape, which affects the drum length and the pulling tension during installation.
The engineering question behind the choice is simply the tensile load. Estimate the mass of the hanging cable: a 4-core 95 mm² armoured cable is around 6 kg/m, so a 60 m vertical drop puts about 360 kg plus a dynamic factor on the armour and the cleats at the top. Tape armour cannot take that. In addition, the wire armour has a much larger metallic cross-section than two tapes, which is one reason it is often a better earth return path for fault current.
Single-core cables break the magnetic rule
Alternating current in a conductor produces an alternating magnetic field around it. In a three-core cable the three fields cancel almost completely outside the cores, so a steel armour around them sees almost no flux and stays cool. Put the same steel armour around a single-core cable and it becomes a shorted single-turn secondary winding: the steel carries circulating currents and hysteresis losses, heats up, and can raise the conductor temperature enough to cut the ampacity by a substantial margin.
That is why a single-core armoured cable should not use magnetic armour. The standard answer is a non-magnetic metallic layer: aluminium wire armour, or in some constructions a stainless steel or brass tape. In the GB/T 12706 code this appears as the digit 6, so a single-core XLPE cable with aluminium wire armour and a PVC sheath is YJV62. Single cores should also be laid in a trefoil group, with the armour bonded at both ends, and the ampacity taken from the single-core columns of the table, which are higher than the multicore values for the same size because the cores are separated and lose heat more easily.
- Never specify steel tape or steel wire armour on a single-core AC cable
- Use aluminium wire armour (code 6) or another non-magnetic construction for single cores
- Install single cores in a trefoil or flat touching formation and keep the three cores of one circuit close together
- Bond and earth the armour at both ends on single-core circuits
- Alternatively, use three-core cable: it avoids the problem, the termination cost and the extra installation discipline
Can the armour be the earth conductor
Yes, in principle, and it is common practice: the armour of YJV22 or YJV32 can serve as the circuit protective conductor if its cross-section is adequate for the fault current and it is properly bonded. The armour of a multicore cable is an earthed metallic layer surrounding the cores, which is a good geometry for a fault return path because it also contains the magnetic field of the fault current.
In practice there are three cautions. The steel cross-section is small compared with a copper conductor of the same current rating, so it needs checking with the adiabatic equation, using the appropriate K value for steel and a temperature limit for the sheath. Joints must bond the armour across, and every gland must make a low-impedance connection to it; a rusty or painted gland defeats the purpose. And where the design calls for a dedicated protective conductor inside the cable, or where the national code requires one, the armour is supplementary rather than primary. Voltcore supplies 3-core, 4-core and 3+1, 3+2 and 4+1 constructions so the protective conductor can be a full-size core when the project demands it.
The selection sequence
Work through the questions in order and the code comes out the other end. Start with the route, not with the cable, because the route determines the mechanical load. The electrical sizing is a separate step that has already been done: current, voltage drop and short-circuit have set the cross-section and the number of cores, and the armour decision does not change them.
The one question people skip is the single-core issue. If the size or the number of parallel runs forces single-core cable, the armour material changes to aluminium and the installation method changes with it. If the answer to any tensile question is yes, tape armour is out.
| Question | If yes | Resulting code |
|---|---|---|
| Is the cable buried directly or in a duct under traffic? | Mechanical crush and impact are the risk | YJV22 |
| Is there a vertical drop, shaft, or unsupported span over about 30 m? | Tensile load on the cable | YJV32 (or YJV42 for thicker wire) |
| Are the cores single-core construction? | Steel armour would heat up | YJV62, aluminium wire armour |
| Is the armour being used as the protective conductor? | Check the steel cross-section against the fault level | YJV32 preferred over YJV22 for fault capacity |
| Is the outer sheath exposed to sunlight or to aggressive soil? | PVC may not be enough | YJV23 or YJV33, polyethylene outer sheath |
| Is the cable in a fire-critical escape route? | Sheath must be low smoke and halogen free | WDZ-YJY23 or equivalent, LSZH outer sheath |
Specification mistakes seen in real RFQs
Most armour problems on site come from the specification, not from the cable. The recurring ones are listed below, and each of them is avoidable with one line on the drawing. The cost of the mistake is rarely the cable: it is the excavation, the jointing and the outage.
- Asking for armoured cable without saying which armour, then receiving tape where wire was needed for a riser
- Ordering single-core YJV32 with steel wire armour, which heats the armour and derates the circuit
- Assuming the armour makes the cable waterproof, then being surprised by water tracking into a joint
- Forgetting to state the outer sheath material, and receiving PVC where the route is in aggressive or chemically contaminated soil
- Using an unarmoured cable in a trench because it was cheaper, then paying for a failed section after the first backfill
- Neglecting the bending radius in a tight pit: 12 × overall diameter is a real constraint on a 240 mm² cable
Frequently asked questions
What is the difference between YJV22 and YJV32?
Both are 0.6/1 kV XLPE insulated with an outer sheath. YJV22 has two layers of galvanised steel tape, which resists crushing and is the standard choice for direct burial. YJV32 has a layer of fine galvanised steel wires, which resists tension and is used for vertical shafts, long unsupported spans and hard pulls. Tape armour will open up under tension; wire armour costs more.
Can I use YJV22 for a vertical riser?
For a short climb where the cable is cleated and its weight is carried by the supports, yes. Once the unsupported weight becomes significant, the tapes cannot carry the load and YJV32 is required. As a working guide, if the drop is long enough that you are calculating the weight of the hanging length, switch to steel wire armour.
Why can single-core cables not use steel armour?
The alternating field around a single conductor induces circulating current and hysteresis loss in a magnetic armour, heating it and reducing the allowable current. In a three-core cable the fields cancel and the effect disappears. Use aluminium wire armour, coded 6, for single-core armoured cable.
Is armoured cable waterproof?
No. The armour is a mechanical layer, and water can still travel along the inside of the cable and between the armour and the cores. For permanently wet routes, water crossings or long vertical runs, specify a construction with water-blocking tapes or powders and sealed conductors, and use water-blocking joints.
Need this worked out for a specific installation?
Send load current, route length, installation method, ambient temperature and the applicable standard — we will return a sized construction with the volt-drop and derating arithmetic shown.