Cable Armouring Wire — What It Is, Why It's Used & How to Specify It

Cable Armouring Wire — The Complete Buyer's Guide

In power distribution and telecommunication, cables are frequently buried underground or laid in harsh industrial cable trenches. To protect the insulated conductor cores from mechanical crushing, rodent chew, and installation strains, cables require mechanical armouring. This guide explains how to specify galvanized steel armouring wire as per IS 3975 standards.

Why Cables Need Armouring

• Mechanical Protection: Prevents physical damage from rocks, soil pressure, or accidental impact during excavation.
• Rodent and Pest Protection: Shields the insulation jacket from insect and rodent attacks which could trigger short circuits.
• Electrical Grounding: In high-voltage installations, the steel armouring serves as a structural earth continuity conductor (ECC) to ground faults.

Types of Cable Armouring Profiles

Underground cables typically use one of two wire profiles for armouring:

Round Steel Wire (SWA - Steel Wire Armour): Round galvanized wires wound helically around the cable. It offers high tensile strength and impact resistance, and is standard for multi-core cables.

Formed Steel Wire (SFA - Steel Flat Armour): Flat galvanized steel wire with a slight curvature. It is preferred for medium and high-voltage cables because formed flat profiles cover a greater percentage of the cable's circumference with less overall thickness and weight.

Key Technical Parameters to Specify

When purchasing armouring wire for cable production, procurement teams must verify and request these parameters in the mill test report:

Technical Parameter	Standard Requirement (IS 3975)	Importance
Electrical Resistivity	Maximum 14.5 Ω/km	Essential for grounding and earthing safety.
Tensile Strength (UTS)	300 to 500 N/mm²	Ensures the wire is ductile enough to bend without snapping.
Elongation Minimum	Minimum 10%	Allows the final cable to remain flexible during installation.
Zinc Coating Continuity	Passes CuSO₄ copper sulfate dip test	Ensures no bare steel spots remain exposed to rust.