For underground installation, overall, SWA armored cables are a better choice than AWA cables. Specifically, they offer higher mechanical strength and better resistance to external pressure and physical damage.
Choosing Between SWA and AWA for Underground Power Distribution
For typical 3-phase underground circuits using multi-core cables (e.g., BS 5467 or IEC 60502), SWA is the technically superior and most cost-effective choice.
Multi-core cables: The industry standard for underground installations is Steel Wire Armor (SWA). It provides superior mechanical protection and high tensile strength. As a result,these properties resist crushing and longitudinal stress during burial.
Single-core AC cables: Aluminum Wire Armor (AWA) is mandatory. This is because,aluminum is non-magnetic, so it prevents eddy currents and induced heating. In contrast,steel armor would cause these problems around a single conductor.
Technical Parameter Comparison: SWA vs. AWA
The following matrix outlines the critical physical and electromagnetic differences between galvanized steel and aluminum armoring layers.
Mechanical Protection and Environmental Durability
The armor serves two key functions: fault current path to earth and mechanical protection for XLPE insulation.
Thermal Performance: Both SWA and AWA cables with XLPE insulation support 90 °C continuous operation and 250 °C short-circuit temperature.
Impact Resistance: SWA offers superior protection against excavation damage.
Chemical Stability: PVC/LSZH sheaths provide basic underground protection. However, lead or chemical-resistant bedding is needed for high-hydrocarbon environments.
Electromagnetic Considerations for Single-Core Cables
In high-voltage or high-current AC applications, using SWA on a single-core cable is a critical failure point. When a single conductor carries AC, it creates a fluctuating magnetic field. This field induces a current in the magnetic steel armor.
This leads to:
Inductive Heating: The armor acts like a shorted transformer turn, potentially melting the outer sheath.
Voltage Drop: Increased impedance due to magnetic losses.
As a solution, Aluminum Wire Armor (AWA) is used. Because aluminum is non-magnetic, the magnetic field passes through it without generating significant heat. Thus, it is the only viable choice for single-core underground feeders.
