Cable Armouring Wire — What It Is, Why It's Used & How to Specify It
Cable armouring wire is a galvanized steel wire (round or formed) applied helically around power and telecom cables to provide mechanical protection, rodent resistance, and electrical grounding. IS 3975:1999 mandates a maximum resistivity of 14.5 Ω/km, tensile strength 300–500 MPa, and minimum 10% elongation.
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. |
All specifications should be verified against BIS IS 3975:1999 standard requirements.
Key Takeaways
- Cable armouring wire provides mechanical protection, rodent resistance, and electrical grounding for underground cables
- Two profiles exist: round wire (SWA) for multi-core cables and formed wire (SFA) for high-voltage cables
- IS 3975:1999 mandates max 14.5 Ω/km resistivity, 300–500 MPa tensile strength, and min 10% elongation
- Copper sulfate dip test verifies zinc coating continuity with no bare steel spots
- Formed wire offers better cable coverage and material efficiency than round wire
Author
Technical Team, Khemji Wire & Wire Pvt. Ltd.
IS 280 & IS 3975 certified wire manufacturing since 1988
This article was reviewed by Khemji Wire's engineering team and reflects IS 280:2006 and IS 3975:1999 standard requirements.
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