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Three suppliers quote the same medium voltage cable specification, with price differences exceeding 15%. The conductor, insulation, and voltage rating are identical.
The difference is the armour type: STA, SWA, or AWA.
Which one to choose? The wrong choice affects safety, service life, and total cost — not just the cable price.
Armour is the cable's protective layer. Each type fits different applications.
Armour Type | Material | Relative Cost | Best For |
STA (Steel Tape Armour) | Galvanized steel tape | Lowest | Fixed installations, crush resistance |
SWA (Steel Wire Armour) | Galvanized steel wire | Medium (10-20% higher than STA) | Direct burial, vertical runs, tensile strength |
AWA (Aluminium Wire Armour) | Aluminium wire | Higher (12-20% higher than STA) | Single-core AC (mandatory) |
Two factors beyond price:
● Weight: AWA is 15-20% lighter than SWA, reducing transport and support structure costs for long-distance projects
● Lead time: STA is shortest (steel tape is standard stock), SWA is medium, AWA requires checking aluminium wire inventory
This rule is the most overlooked and has the most severe consequences.
Why?
When AC flows through a single-core cable, it generates a magnetic field around the conductor. If the armour is steel (a ferromagnetic material), it induces eddy currents in the armour, causing heating. The heat continuously degrades the insulation, eventually leading to breakdown.
Why can multi-core cables use steel armour? The magnetic fields of three-phase currents cancel each other out, producing no significant eddy currents.
Quantified impact:
Eddy current losses from magnetic armour can cause significant derating. The same cable with steel armour may only carry 60-70% of its rated current, while aluminium armour allows full rating.
Regulatory requirement: IEC 60502-2 explicitly requires non-magnetic armour for single-core cables.
Selection Guide
Criterion | Choose STA | Choose SWA | Choose AWA |
Core count | Multi-core | Multi-core | Single-core (mandatory) |
Current type | AC or DC | AC or DC | AC (mandatory) |
Installation | Direct burial, tray, duct | Direct burial, vertical, underwater | Single-core AC |
Primary stress | Crush resistance | Tensile strength | Eddy current elimination |
Cost priority | Lowest | Medium | Function first |
Different environments require specific armour and sheath combinations:
Installation Environment | Recommended Armour | Recommended Sheath | Reason |
Direct burial | SWA/STA | PE | Low water absorption, crush resistance |
Tray / Cable trench | STA (multi-core) / AWA (single-core) | PVC | Cost-effective general protection |
Indoor / Buildings | Unarmoured or STA | LSZH | Fire safety priority |
Coastal / Corrosive | AWA | PE | Salt spray resistance |
Tunnels / Underground galleries | SWA/STA | LSZH | Mechanical + fire protection |
Different markets apply different standards. Confirm before purchasing:
Standard System | Applicable Regions | Typical Standard |
IEC | Europe, Middle East, Southeast Asia, Africa | IEC 60502-2 |
ICEA (North America) | USA, Canada | ICEA S-93-639, S-94-649 |
BS (UK) | UK and Commonwealth | BS 6622 |
AS/NZS (Australia/New Zealand) | Australia, New Zealand | AS/NZS 1429.1 |
Two key points:
● Non-magnetic armour requirement is global — IEC, ICEA, BS, and AS/NZS all require non-magnetic armour for single-core AC cables
● Compliance does not mean cross-market compatibility — an IEC-compliant cable may not meet North American AEIC/ICEA standards (additional aging tests required)
If you are unsure which armour type fits your project, or if you need support in reviewing your technical specification, contact our team for a no-obligation consultation.
Tel: +86-371-6054 7601
WhatsApp / WeChat: 0086 135 9887 3045
Email: Admin@cncablegroup.com
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