In complex electrical engineering projects, cables function much like the vascular system in the human body - they carry vital energy that powers entire systems. Selecting the appropriate cable type is as crucial as maintaining healthy blood vessels, directly impacting the safety and efficiency of the entire electrical infrastructure. Among armored cable options, Steel Wire Armored (SWA) cables play a pivotal role in power transmission, with insulation material selection being particularly critical. But how does one choose between thermoplastic (PVC) and thermosetting (XLPE) SWA cables?

Steel Wire Armored (SWA) cables feature a protective layer of steel wire that provides exceptional mechanical protection against impacts, crushing forces, and tension. This makes them ideal for demanding environments including direct underground burial, conduit installations, and industrial settings requiring robust protection.

The core components of SWA cables include:

• Conductor (typically copper or aluminum)
• Insulation layer
• Inner sheath
• Steel wire armor
• Outer sheath

The insulation material critically affects the cable's electrical performance, temperature resistance, and service life. The two primary insulation materials for SWA cables are Polyvinyl Chloride (PVC) and Cross-linked Polyethylene (XLPE).

As a thermoplastic material, PVC offers good electrical insulation, chemical resistance, and flame retardancy at relatively low cost, making it historically popular for low-voltage cables including early SWA cables. However, PVC has significant limitations:

• Maximum continuous operating temperature of 70°C
• Prone to aging and deformation at high temperatures
• Potential toxic gas emission under extreme heat
• Lower mechanical strength and abrasion resistance

Through a specialized cross-linking process that creates a three-dimensional molecular structure, XLPE achieves:

• Continuous operating temperature of 90°C (130°C short-term overload)
• Enhanced mechanical strength and chemical resistance
• Superior aging resistance and crack prevention
• Longer service life

Modern SWA cables predominantly use XLPE insulation compliant with standards including:

• BS 5467: Thermosetting insulated armored cables for fixed installations (600/1000V & 1900/3300V)
• BS 6724: Low-smoke, low-halogen cables for fire-sensitive environments
• BS 7846: Fire-resistant cables maintaining circuit integrity during fires

Compared to PVC alternatives, XLPE SWA cables offer:

• Higher current capacity: Enables use of smaller cable sizes for equivalent loads
• Enhanced thermal stability: Maintains performance in high-temperature environments
• Superior insulation resistance: Reduces leakage current risks
• Improved mechanical protection: Better withstands physical stresses
• Chemical resistance: Suitable for corrosive environments like chemical plants

Even XLPE-insulated SWA cables may use PVC for inner/outer sheaths. For indoor installations with strict fire safety requirements, Low Smoke Zero Halogen (LSZH) sheaths are recommended to minimize toxic emissions during fires.

Key factors when specifying SWA cables:

BS 7671 Appendix 4 provides current ratings:

• Table 4D4A: Thermoplastic (PVC) cables
• Table 4E4A: Thermosetting (XLPE) cables

BS 7671 512.1.5 requires equipment compatibility verification when connecting to conductors rated above 70°C. This may necessitate either:

• Selecting PVC cables with equivalent current capacity
• Using equipment rated for 90°C operation

Thermosetting insulation allows higher k-values (143 vs. 115 for PVC) when calculating fault current effects, providing greater safety margins.

Recommendations for specific applications:

• High-load/high-temperature environments: XLPE preferred
• Fire-sensitive locations: XLPE with LSZH sheath
• 70°C-rated equipment: Equivalent PVC or upgraded components

Professional electrical engineering consultation and adherence to relevant standards (BS 7671, IEC 61439) remain essential for optimal cable selection and system safety.