Walk into any large construction site, industrial facility, or infrastructure project and you will find armoured cable running through it. Underground, along walls, through cable trays, buried in the ground. It is one of the most widely used cable types in electrical installation work, and yet it is also one of the most commonly misunderstood.
Contractors sometimes specify armoured cable out of habit on every project. Others skip it in situations where it is genuinely needed and end up dealing with damaged cables, safety issues, and costly repairs down the line. Neither approach is ideal.
This guide will give you a clear, practical understanding of what armoured cable actually is, how it is built, what the different types mean, and when you genuinely need it versus when a simpler cable will do the job. If you are sourcing electrical cables for your next project, understanding this distinction will save you time, money, and headaches.
What Is an Armoured Cable?
An armoured cable is an electrical cable that has an additional layer of mechanical protection built into its construction. That protective layer sits between the inner core assembly and the outer sheath, and it is made from either galvanised steel wire or aluminium wire wound tightly around the cable.
The purpose of this armour layer is straightforward: it stops the cable from being crushed, cut, punctured, or damaged by the external environment. Without it, standard insulated cables are vulnerable to physical impact, ground movement, rodent attack, and a range of other hazards that exist in outdoor, underground, and industrial settings.
Armoured cables are also commonly referred to as SWA cable (Steel Wire Armoured), AWA cable (Aluminium Wire Armoured), mains cable, or power cable, depending on the context and the specific type being used.
It is worth noting something that surprises many people: the armour itself does not make the cable waterproof or weatherproof. It provides mechanical protection. The cable still needs appropriate insulation and sheathing materials if it will be exposed to moisture, chemicals, or UV radiation.
How Is an Armoured Cable Constructed?
Understanding the construction of an armoured cable helps you make sense of the product specifications you will see on data sheets. A typical armoured cable is built in layers, each serving a specific function.
Layer 1: The Conductor
At the centre of the cable are the conductors, which carry the electrical current. Most armoured cables use plain stranded copper conductors to Class 2 standard (as defined in BS EN 60228), which means they are rigid stranded copper rather than finely stranded flexible conductors. Some versions use aluminium conductors as a lower-cost alternative, though copper remains the standard choice for most applications where reliability is the priority.
Layer 2: The Insulation
Each conductor is individually insulated. The most common insulation material in modern armoured cables is XLPE (Cross-Linked Polyethylene), which offers excellent electrical properties, good resistance to water and chemicals, and a maximum conductor operating temperature of 90°C. Some older specifications and lower-cost products use PVC insulation, which has a lower temperature rating of 70°C.
Layer 3: The Bedding
After the insulated cores are laid up together, a bedding layer is applied over them. This is typically an extruded PVC compound. The bedding serves two purposes: it provides a smooth, circular form for the armour to sit on, and it acts as a protective cushion between the inner cores and the armour wires.
Layer 4: The Armour
This is the defining layer of an armoured cable. Galvanised steel wires or aluminium wires are wound helically around the bedding layer. This armour provides the mechanical protection that the cable is known for, giving it resistance to crushing, impact, rodent damage, and high tensile pulling loads during installation.
The choice between steel and aluminium armour is not arbitrary, and we will explain that distinction in the next section.
Layer 5: The Outer Sheath
The outermost layer is the outer sheath, which protects the armour and inner construction from the environment. The sheath material is typically PVC (black, with carbon loading for UV resistance in outdoor applications) or LSZH (Low Smoke Zero Halogen) for installations in enclosed public spaces where fire safety is a priority.
LSZH sheathing became mandatory in the London Underground following the King’s Cross fire in 1987, and is now recommended or required in many public buildings, tunnels, and high-density occupied spaces.
SWA vs AWA: What Is the Difference and Which One Do You Need?
This is the question that catches a lot of people out. Both SWA and AWA are armoured cables, but they are not interchangeable, and using the wrong one in the wrong application creates real problems.
Steel Wire Armoured (SWA) Cable
SWA cable uses galvanised steel wires as the armour layer. Steel provides excellent mechanical strength: it resists crushing, cutting, and impact extremely well, and it allows the cable to withstand high tensile loads, which is important during installation when cables are pulled through conduits or cable trays.
SWA is used for multicore cables only. The reason is important: steel is magnetic. When alternating current flows through a cable, it generates a magnetic field. In a multicore cable, the magnetic fields from the different cores effectively cancel each other out, so very little current is induced into the steel armour. This means SWA works safely in multicore configurations.
The voltage rating of a standard SWA cable is 600/1000V. You will frequently see reference to British Standard BS5467 (PVC sheathed) or BS6724 (LSZH sheathed) when specifying SWA cable.
Aluminium Wire Armoured (AWA) Cable
AWA cable uses aluminium wires as the armour layer. Aluminium is non-magnetic, which is the critical difference.
In a single-core cable, there is no neighbouring core to cancel out the magnetic field. If you were to use steel armour on a single-core AC cable, the magnetic field would induce eddy currents in the steel wire. Because steel has higher resistance than aluminium, those induced currents would generate heat in the armour, creating a risk of overheating and cable failure.
Aluminium armour solves this problem. It is non-magnetic, so it does not behave the same way under a magnetic field. Any induced currents that do form are conducted away to earth efficiently rather than generating heat.
Key Rule: Single-core armoured cable always uses AWA (aluminium wire armour). Multicore armoured cable typically uses SWA (steel wire armour). If you see a single-core SWA cable specified, query it before proceeding. |
Steel Tape Armoured (STA) Cable
There is a third type worth mentioning: Steel Tape Armoured (STA) cable. Instead of individual wires wound around the cable, STA uses one or two layers of steel tape wrapped around the bedding. This provides excellent crush resistance but lower tensile strength compared to SWA. STA is commonly used for direct burial in trenches and for fibre optic cable protection, where longitudinal mechanical loads are less of a concern.
When Should You Use Armoured Cable?
This is the practical heart of the matter. Armoured cable costs more than standard unarmoured cable. It is heavier and less flexible, which makes it harder to handle and install. You should use it when the installation environment genuinely demands mechanical protection. Here are the situations where armoured cable is either required or strongly advisable.
Direct Burial Underground
This is the most common application for armoured cable. When a cable is buried directly in the ground without a protective conduit or duct, it faces genuine risks: ground movement, excavation by other trades, rodents chewing through it, and accidental damage from future digging work.Armoured electrical cables are designed to withstand all of these.
For direct burial applications, you also want to ensure the cable has an appropriate outer sheath for the soil conditions and any presence of moisture or chemicals in the ground. Black PVC with carbon loading (UV stabilised) is the standard outdoor sheath. In aggressive soil conditions, you may need to specify additional chemical resistance.
Outdoor Above-Ground Installations
Running cables along external walls, between buildings, along cable ladder or tray on the outside of a structure: all of these qualify as applications where armoured cable adds genuine value. Even when the cable is not underground, it faces UV radiation, temperature cycling, and the risk of physical impact or interference from vehicles, tools, or wildlife.
Industrial and Factory Environments
Industrial sites put cables through a lot. Forklift trucks, heavy machinery, falling objects, chemical splashes, oil exposure, high ambient temperatures. In these environments, standard unarmoured cable does not last. Armoured cable provides the layer of toughness that keeps the installation reliable over the long term.
For fixed power distribution in industrial facilities, SWA cable is the standard specification. It is used to supply distribution boards, machinery, lighting circuits, and motor control centres. Pair this with quality cable glands at termination points to maintain the integrity of the mechanical protection all the way to the equipment.
Power Distribution in Commercial Buildings
In commercial buildings, armoured cable is commonly used for the main power distribution runs between the incoming supply, main switchboard, sub-distribution boards, and major plant rooms. These are critical circuits that need to be robust and long-lasting. Running them in SWA cable gives the installation resilience and reduces the risk of accidental damage during building maintenance or future fit-out work.
Locations Exposed to Rodent Activity
Rodents are a genuine threat to standard PVC cables. Rats and mice will chew through unarmoured cables without much difficulty. In agricultural buildings, food processing facilities, warehouses, and anywhere with known rodent activity, armoured cable is a sensible baseline specification. The steel or aluminium wire armour is not impervious to a very determined rodent, but it is significantly more resistant than a PVC sheath alone.
Areas with High Mechanical Risk
Cable runs through plant rooms, service corridors, loading bays, and anywhere that sees significant foot and vehicle traffic are candidates for armoured cable. The additional mechanical protection reduces the risk of accidental damage that might be caused by someone dropping a tool on the cable, running a trolley over it, or catching it with equipment.
Vertical Cable Runs
When cables are run vertically over any significant height, they need to support their own weight. SWA cable can withstand the tensile loads involved in a vertical installation better than standard cable, which may deform or strain at the termination points if it is carrying its own weight over a tall run. This is relevant in multi-storey buildings and tall industrial structures.
When Do You NOT Need Armoured Cable?
Equally important is knowing when armoured cable is unnecessary. There is no point paying a premium and dealing with the handling challenges of armoured cable in situations where simpler alternatives work perfectly well.
You typically do not need armoured cable when:
- Cables are installed inside conduit or trunking: A cable running inside a rigid metal conduit or PVC trunking already has mechanical protection. Adding armour on top is redundant in most cases.
- Cables are installed in accessible, indoor locations: Cables clipped to a wall inside a building, running through a ceiling void, or installed in a clearly marked cable tray that is not exposed to physical hazard generally do not need armoured construction.
- Flexible connections to equipment: For short, flexible connections to machinery or equipment that moves, a rubber flexible cable is a far better choice than armoured cable. The armour adds stiffness that works against flexibility. Our rubber flexible cables (H07RN-F) are designed precisely for this kind of application.
- Low-voltage signal and control wiring in protected environments: For instrumentation and signal control cables installed inside control panels or in well-protected indoor locations, armoured construction is usually not required unless the environment specifically demands it.
Armoured Cable Core Configurations
Armoured cables come in a range of core configurations to match different circuit requirements. Understanding the typical options helps you select the right product for your application.
Single-Core
Used where a separate cable is run for each phase, or for high-current single-phase circuits. Always specified with AWA (aluminium wire armour) for AC applications. Commonly used in large power distribution systems where each phase conductor runs separately.
Two-Core
Suitable for single-phase circuits with a live and neutral conductor, or for DC circuits. Used in applications like garden power supplies, outdoor lighting, and small sub-circuits.
Three-Core
The standard choice for three-phase circuits without a neutral, or for single-phase circuits where a separate earth conductor is required alongside live and neutral. Widely used in motor supplies and three-phase equipment connections.
Four-Core and Five-Core
Four-core cable suits three-phase and neutral circuits. Five-core adds a separate earth conductor, which is increasingly specified in modern installations where you want a dedicated earth rather than relying on the armour as the circuit protective conductor.
Cable cores are also available in multi-core configurations up to 48 cores for auxiliary control and instrumentation applications, which links to our range of signal control cables for more complex systems.
SWA as an Earth Conductor: What You Need to Know
One detail that generates a fair amount of discussion among electrical engineers and installers is whether the steel wire armour of an SWA cable can serve as the circuit protective conductor (CPC), which is the technical term for the earth conductor.
The short answer is that the armour can function as a CPC, and this practice is widely used. However, there are important caveats. The armour is not a dedicated earth conductor. Its resistance characteristics are different from a copper earth conductor of equivalent cross-section, and there are conditions under which relying on the armour alone as the CPC may not meet the requirements of the wiring regulations for the fault loop impedance of the circuit.
In practice, many engineers and specifiers now prefer to use a four-core or five-core cable with a dedicated earth core rather than relying on the armour as the CPC. This removes ambiguity and ensures clear compliance with earthing requirements. It also makes testing and fault finding simpler.
If you are in any doubt about earthing arrangements for your specific installation, this is a topic
to resolve with your electrical designer or a qualified engineer before proceeding.
Installation Considerations for Armoured Cable
Armoured cable is designed to be robust, but it still needs to be installed correctly to perform as intended. Here are the key practical points.
Minimum Bending Radius
Armoured cable has a minimum bending radius that must be observed during installation and routing. Bending the cable too sharply can damage the armour wires, deform the insulation, or create stress at the point of bend that leads to early failure. As a general rule, the minimum bending radius is approximately six times the overall cable diameter for multicore SWA cable, though you should always check the specific manufacturer’s data sheet.
Minimum Installation Temperature
PVC-sheathed SWA cable should not be installed at temperatures below 0°C, as PVC becomes brittle in very cold conditions and may crack if the cable is bent. LSZH sheathed versions typically have a lower installation temperature limit. Check the data sheet for the specific product you are using.
Cable Glands
Armoured cable must be properly terminated using the correct cable glands. The gland grips the armour and maintains the integrity of the mechanical protection at the point where the cable enters equipment or an enclosure. Using the wrong gland, or failing to properly clamp the armour, defeats the purpose of using armoured cable in the first place.
Cable glands for SWA cable are available in brass, stainless steel, and nylon, with various IP ratings. For outdoor and industrial applications, brass or stainless steel glands with appropriate sealing are standard.
Cable Support and Cleating
For above-ground cable runs, armoured cable needs to be properly supported at regular intervals using cable clips, cleats, or cable trunking and trays. For single-core cables in particular, trefoil cable cleats are specified to manage the electromagnetic forces that develop between the phases under fault conditions. This is a safety requirement, not an optional extra.
Burial Depth
For direct burial applications, cables must be buried at the correct depth to avoid damage from surface activities. Typical minimum burial depths are 500mm under a footpath and 600mm to 900mm under a road or driveable surface, though local regulations and project specifications may require more. A marker tape should always be buried above the cable to warn future excavators.
Installation Tip: Always allow sufficient cable length at both ends before cutting. Armoured cable is difficult to extend or splice neatly once installed. Measure twice and cut once. It is worth the extra few minutes. |
How Long Does Armoured Cable Last?
When correctly specified for the environment and properly installed, armoured cable has an excellent service life. Industry guidance typically cites a lifespan of 25 to 40 years or more for armoured power cables in normal conditions.
The factors that most significantly affect cable lifespan are:
- Installation quality: Cables that are kinked, bent too sharply, or poorly terminated during installation suffer stress from day one. Good installation practice pays dividends over the life of the cable.
- Environmental exposure: Cables in aggressive chemical environments, extreme temperatures, or constant UV exposure will age faster than cables in benign conditions. Always match the cable specification to the environment.
- Loading: Running cables consistently at or near their maximum current-carrying capacity accelerates thermal ageing of the insulation. Size your cables generously if the load is expected to grow, or if the installation is in a location where heat dissipation is limited.
Mechanical damage: Cables that have been damaged during or after installation will have a shorter effective life. Periodic inspection of accessible cable runs is good maintenance practice.Lorem ipsum dolor sit amet, consectetur adipiscing elit. Ut elit tellus, luctus nec ullamcorper mattis, pulvinar dapibus leo.
Choosing the Right Armoured Cable: A Quick Reference
To bring everything together, here is a practical summary for selecting the right armoured cable for common scenarios.
- Underground garden or site cable: 2 or 4 core SWA, PVC sheathed, 600/1000V rating. Standard choice for supplying outbuildings, site compounds, and external power points.
- Three-phase industrial power supply: 4 core SWA (copper conductor, XLPE insulation), sized to the load. Use a dedicated earth core rather than relying on the armour as the CPC.
- Main distribution cable in a commercial building: Multicore SWA, XLPE insulated, sized to the load and voltage drop requirements. LSZH sheath if running through common areas or escape routes.
- Single-phase supply to external lighting or equipment: 2 or 3 core SWA, suitable sheath for outdoor installation.
- Large single-phase or single-core power circuit: Single-core AWA cable. Never specify single-core SWA for AC applications.
- High fire safety requirement (tunnels, stations, public buildings): SWA cable with LSZH sheath (BS6724). Confirm the specific fire performance standard required for the project.
If you are working through a project specification and want to discuss the right cable product for your requirements, our team at Translight can help. We carry a comprehensive range of electrical cables including SWA and AWA armoured cables from leading manufacturers. Get in touch via our contact page and we will work through the details with you.
Final Thoughts
Armoured cable is one of those products where getting the specification right really matters. Over-specify it and you waste money and make installation harder than it needs to be. Under-specify it and you end up with damaged cables, safety risks, and expensive remedial work.
The key principles to take away are: use armoured cable where mechanical protection is genuinely needed, choose SWA for multicore and AWA for single-core AC applications, match the sheathing to the environment, and terminate it properly with the correct cable glands and support systems.
If you found this guide useful, you might also want to read our overview of Nexans cable types which covers the full spectrum of power and data cable options available for modern electrical projects. And if you need support sourcing the right armoured cable for your project, our team at Translight is ready to help.
