What Is the Function of a Cable Armor Layer?

The armor layer in electrical cables is a critical component designed to enhance the durability and safety of cables used in power distribution, industrial applications, and other demanding environments. Typically found in low-voltage (0.6/1 kV) and medium-voltage (3.6/6 kV to 26/45 kV) cables, the armor layer protects the cable’s inner components from external stresses, ensuring reliable performance and compliance with standards such as IEC 60502. This guide details the functions, types, applications, and considerations of cable armor layers, presented in a formal and structured manner.

Table of Contents

1. Overview of Cable Armor Layer

The armor layer is a protective covering in electrical cables, typically placed between the inner insulation (e.g., XLPE, PVC) and the outer sheath (e.g., PVC, PE). It is made of materials like steel wire, steel tape, or aluminum, designed to withstand mechanical and environmental stresses. Armored cables are used in applications requiring enhanced protection, such as underground installations, industrial plants, or areas prone to physical damage. The armor layer ensures the cable’s conductors and insulation remain intact, maintaining electrical performance and safety over a lifespan of 25–30 years.

2. Functions of the Armor Layer

The armor layer serves multiple functions to enhance cable performance and safety:

• Mechanical Protection:
  • Shields cables from physical damage, such as impact, crushing, or abrasion, during installation or operation.
  • Protects against external forces, e.g., heavy machinery in industrial settings or rocks in underground burials.
• Environmental Protection:
  • Resists moisture ingress, rodents, and termites, which can degrade insulation in harsh environments like underground or outdoor installations.
  • Enhances durability in corrosive environments (e.g., chemical plants) when combined with appropriate sheathing.
• Electromagnetic Interference (EMI) Shielding:
  • Metallic armor (e.g., steel wire) reduces EMI from external sources (e.g., motors, power lines), protecting signal integrity in control or communication cables.
  • Acts as a partial shield for radiated EMI, complementing dedicated shielding layers in sensitive applications.
• Structural Integrity:
  • Provides tensile strength to withstand pulling forces during installation (e.g., up to 50 kN for steel wire armored cables).
  • Maintains cable shape, preventing deformation under mechanical stress.
• Grounding Path:
  • Serves as a grounding conductor in some designs, dissipating fault currents to ensure safety (e.g., in MV cables per IEC 60502-2).

3. Types of Armor Layers

Armor layers vary by material and construction, each suited to specific applications:

• Steel Wire Armor (SWA):
  • Construction: Galvanized steel wires wound helically around the cable core.
  • Features: High tensile strength (e.g., 50–70 kN), excellent for underground or direct burial applications.
  • Use: LV and MV power cables (e.g., XLPE/SWA/PVC for 0.6/1 kV).
• Steel Tape Armor (STA):
  • Construction: Steel tapes wrapped longitudinally or helically around the cable.
  • Features: Provides crush resistance but lower tensile strength than SWA; more compact design.
  • Use: Indoor or ducted installations where pulling forces are minimal.
• Aluminum Wire Armor (AWA):
  • Construction: Aluminum wires wound helically, used primarily in single-core MV cables.
  • Features: Lighter than SWA, non-magnetic to avoid eddy currents in single-core cables.
  • Use: MV cables (e.g., 8.7/15 kV single-core XLPE/AWA).
• Braided Armor:
  • Construction: Woven metallic wires (e.g., tinned copper) for flexible cables.
  • Features: Provides EMI shielding and moderate mechanical protection; flexible for dynamic applications.
  • Use: Control or instrumentation cables in industrial settings.

4. Applications of Armored Cables

Armored cables are used in environments requiring robust protection:

• Underground Installations:
  • SWA cables protect against soil pressure, rocks, and moisture in direct burial applications (e.g., 0.6/1 kV XLPE/SWA/PVC).
• Industrial Facilities:
  • Used in chemical plants, refineries, and factories to withstand mechanical damage from machinery or heavy traffic.
• Utility Networks:
  • MV cables (e.g., 8.7/15 kV with AWA) for power distribution in urban or rural grids, protecting against environmental hazards.
• Control and Instrumentation:
  • Braided armor cables reduce EMI in sensitive control systems (e.g., PLC networks in industrial automation).
• Marine and Offshore:
  • Armored cables resist moisture and mechanical stress in shipboard or offshore platform installations.

5. Practical Considerations

When selecting and using armored cables, consider the following:

• Armor Type Selection:
  • Choose SWA for high tensile strength in underground or heavy-duty applications; AWA for single-core MV cables to avoid magnetic losses.
• Installation Requirements:
  • Adhere to minimum bending radii (e.g., 12–15 times cable diameter for SWA) to avoid damaging armor or insulation.
  • Use proper glands to maintain armor continuity and grounding.
• Cost vs. Protection:
  • Armored cables are more expensive than unarmored ones. Use unarmored cables in low-risk environments to reduce costs.
• Environmental Compatibility:
  • Pair armor with corrosion-resistant sheathing (e.g., PVC, PE) for humid or chemical environments.
• Standards Compliance:
  • Ensure cables meet IEC 60502, BS 5467, or regional standards (e.g., CCC for China, CE for Europe).

6. Challenges and Solutions

7. Conclusion

The armor layer in electrical cables provides essential mechanical, environmental, and EMI protection, ensuring durability and safety in demanding applications like underground power distribution, industrial facilities, and utility networks. By selecting the appropriate armor type—such as SWA for tensile strength, AWA for MV cables, or braided armor for flexibility—and following proper installation practices, users can enhance cable reliability and compliance with standards like IEC 60502. Addressing challenges like cost and corrosion through strategic selection and maintenance ensures armored cables deliver optimal performance over a lifespan of 25–30 years.