Pianificazione di un'installazione di cavi sotterranei? One of the most critical decisions is choosing between armored and unarmored cables. La scelta sbagliata può portare al guasto prematuro del cavo, costose riparazioni degli scavi, o gravi rischi per la sicurezza. Questa guida analizza le differenze strutturali, livelli di protezione, norme CEI applicabili, and real-world use cases — so you can select the right cable type for your project.
Core Structural Differences Between Armored and Unarmored Cables
The fundamental difference between these two cable types lies in their physical construction — and that difference directly determines how they perform underground.
Armored cables (also written as armoured cables outside North America) include an additional metallic reinforcement layer between the inner insulation and the outer sheath. This armour is typically made from:
- Steel wire armour (SWA) — the most common type for direct burial, offering high radial crush resistance (typically ≥3,000 N/cm per IEC 60502-2 requirements)
- Armatura in nastro d'acciaio (STA / DSTA) — double steel tape for high-pressure environments
- Aluminium wire armour (AWA) — used for single-core cables to avoid eddy current losses
Al contrario, unarmored cables consist only of conductor, isolamento, and an outer polymeric sheath (PVC, LSZH, or PE). They contain no metallic reinforcement layer and rely entirely on conduit or duct systems for mechanical protection when installed underground.
Both types are manufactured across a wide voltage range — from 0.6/1kV low voltage (covered by IEC 60502-1) Attraverso 6kV–30kV medium voltage (CEI 60502-2) fino a 66kV–150kV high voltage (CEI 60840) — in conductor cross-sections from 1.5mm² to 1,000mm² in copper or aluminium.
Mechanical Protection: How Armored and Unarmored Cables Handle Underground Stress
Underground environments present constant mechanical threats: sharp rock fragments, shifting clay soils, root growth, and surface load pressure from vehicles or structures above. The mechanical protection gap between these two cable types is substantial.
Armored cables are engineered for direct burial without conduit. Steel wire armour provides radial crush resistance typically exceeding 3,000 N/cm, sufficient to withstand compacted backfill pressure, rocky subsoil, and the stress of mechanical excavation nearby. Inoltre, armored cables resist tensile loads during pulling installation — steel wire armour on large HV cables can sustain pulling tensions exceeding 50 kN depending on conductor cross-section.
Unarmored cables, however, offer only minimal mechanical protection. Their polymeric sheath can withstand light surface abrasion during handled installation, but provides essentially no resistance to point loads from sharp rocks, root penetration, or compaction pressure. As a result, unarmored cables installed underground without conduit will typically fail within 2–5 years in all but the most benign soil conditions.
The practical implication is straightforward: for direct burial, armored cable is the only technically acceptable option under IEC 60502. Unarmored cables used underground must be routed through high-density polyethylene (HDPE) or rigid PVC conduit for their entire length, with conduit rated to the expected soil load.
Resistenza ambientale: IEC Standards and Underground Hazard Performance
Beyond mechanical threats, underground cable installations face moisture ingress, corrosive soils, biological attack from rodents and termites, and electromagnetic interference (EMI) from parallel power lines or industrial equipment.
Armored cables address all of these hazards simultaneously. The steel or aluminium armour layer provides:
- Moisture resistance: When combined with a lead sheath or moisture-barrier tape (required for cables ≥110kV under IEC 60840), armored HV cables achieve 100% radial waterproofing suitable for submarine or permanently flooded installations.
- Corrosion protection: An extruded polyethylene (PE) or PVC oversheath protects the armour from soil corrosion; bitumen-coated armour is available for highly aggressive soils.
- Rodent and termite resistance: The metallic armour layer physically prevents rodent chewing — a critical requirement in tropical and subtropical regions where cable damage from pests is a common cause of network failure.
- Electromagnetic shielding: The armour acts as a Faraday cage, significantly attenuating EMI from adjacent power circuits. This makes armored cables the required choice for installations near variable-frequency drives (VFDs), switchgear, or high-voltage transmission lines.
Unarmored cables, in contrast, offer limited environmental resistance. With no metallic layer, they have minimal water resistance beyond their sheath rating, no EMI shielding, and no defence against rodent attack. They are suitable only for dry, low-risk environments — typically indoors or inside pre-installed conduit in benign soil conditions.
Ideal Underground Use Cases for Armored and Unarmored Cables
Selecting the correct cable type requires matching the cable specification to the actual installation environment:
Choose armored cables (SWA / AWA / DSTA) for:
- Direct burial in soil, rock, or mixed geological conditions (minimum burial depth: 600mm for LV, 800mm for MV per typical IEC 60364 guidance — verify local grid codes)
- High-load utility trenches beneath roads, railways, or heavy equipment zones
- Rocky subsoil where mechanical excavation could damage unprotected cables
- Installations with high electromagnetic interference (zone industriali, sottostazioni, VFD environments)
- Underground wiring in explosive or hazardous classified areas (oil and gas sites, miniere) — use appropriately certified armored cables to IEC 60079 or equivalent
- Medium voltage (6kV–35kV) e alta tensione (66kV–500kV) underground transmission
Choose unarmored cables for:
- Installations inside pre-installed HDPE or rigid PVC conduit for the full route length
- Indoor wiring in cable trays, conduit, or trunking
- Short, controlled temporary surface runs with no burial requirement
- Low-risk, dry environments with no mechanical damage exposure
Cost and Installation Tradeoffs
Protection always involves practical cost and installation tradeoffs that must be factored into project budgets.
Armored cables carry a 15–35% higher material cost per metre compared to equivalent unarmored specifications, depending on cable size and armour type. Their metallic layer increases cable weight and reduces flexibility — a 240mm² SWA cable typically weighs 5–8 kg/m, compared to 3–5 kg/m for an unarmored equivalent. During installation, a larger bending radius must be maintained (typically 12–15× overall cable diameter for SWA cables). The armour must also be correctly bonded and grounded at termination points to prevent induced current circulation.
That said, armored cables eliminate the need for conduit in direct burial applications. In large projects, the conduit cost savings often offset the higher cable material cost, making armored cable the more economical overall solution for buried runs exceeding 50–100 metres.
Unarmored cables cost less per metre and are lighter and more flexible — easier to handle in confined spaces and faster to terminate. Tuttavia, full conduit installation for underground use typically adds USD 8–20 per metre of run in materials and labour, depending on conduit type, trench depth, and local market conditions. For underground runs where conduit must be installed from scratch, the total installed cost of an unarmored system often exceeds that of a direct-burial armored cable solution.
Final Selection Summary
For the majority of direct underground burial projects, armored cable is the technically correct and often more cost-effective long-term choice. Unarmored cable is appropriate for underground use only when full conduit infrastructure is already in place for the entire cable route, and the site presents no mechanical, ambientale, or electromagnetic hazards.
When specifying cables for any project, confirm the applicable IEC standard (CEI 60502-1 for LV, CEI 60502-2 for MV, CEI 60840 or IEC 62067 for HV), the required armour type, materiale conduttore (rame o alluminio), and outer sheath material (PVC, LSZH, or PE) based on your soil conditions and environmental requirements.
FAQs
1. Can armored cable be buried directly underground without conduit? SÌ. Armored cables with steel wire armour (SWA) or double steel tape armour (DSTA) are specifically designed for direct burial to IEC 60502-2 e CEI 60840 standard. They withstand radial crush loads of ≥3,000 N/cm, making them suitable for rocky subsoil, high-traffic load zones, and deep trenching. Minimum burial depth is typically 600mm for LV and 800mm for MV cables, though local grid codes may specify greater depths.
2. Do I need conduit for unarmored cable underground? Yes — without exception. Unarmored cables have no metallic reinforcement and cannot resist point loads from rocks, root pressure, or soil compaction. CEI 60502-1 does not classify unarmored cables as suitable for direct burial. They require installation inside high-density polyethylene (HDPE) conduit or equivalent rigid duct for the entire underground run length.
3. What is the main advantage of armored cable for underground use? Armored cables provide simultaneous mechanical protection (crush resistance ≥3,000 N/cm), moisture resistance, corrosion protection, rodent resistance, and electromagnetic shielding — eliminating the need for separate conduit infrastructure in direct burial projects. For medium and high voltage applications (6kV and above to IEC 60502-2 e CEI 60840), armored cable is the standard specification for underground transmission worldwide.
4. Is unarmored cable cheaper than armored cable for underground projects? Per metre of cable, unarmored cable is typically 15–35% cheaper than an armored equivalent. Tuttavia, the mandatory conduit installation for underground use adds USD 8–20 per metre of installed cost. For direct burial runs exceeding 50–100 metres, armored cable is typically more economical overall, as it eliminates conduit costs entirely.
5. When should I choose unarmored cable for underground use? Unarmored cable is appropriate for underground installation only when: (a) full HDPE or rigid PVC conduit is already installed for the complete route length; (b) the soil is stable, non-corrosive, and free of mechanical hazards; (c) no significant rodent or termite activity is present; E (d) no electromagnetic interference from adjacent power circuits is expected. In any other scenario, armored cable is the safer and more reliable choice.
6. What IEC standards apply to armored and unarmored underground cables? The key IEC standards are: CEI 60502-1 (power cables with extruded insulation and accessories for rated voltages from 1kV up to and including 3kV), CEI 60502-2 (rated voltages from 6kV up to and including 30kV), CEI 60840 (rated voltages above 30kV up to and including 150kV), e CEI 62067 (above 150kV up to and including 500kV). Both armored and unarmored constructions are covered within each standard, with construction requirements for armour specified in the relevant annexes.
About XWA Power — Armored and Unarmored Cable Manufacturer
XWA Power Co., Ltd. is a professional power cable manufacturer based in Xiangcheng, Provincia dell'Henan, Cina, supplying both armored and unarmored cables across the full voltage range from 0.6/1kV to 500kV.
Our cable range includes steel wire armoured (SWA), aluminium wire armoured (AWA), double steel tape armoured (DSTA), and unarmoured XLPE and PVC insulated cables to IEC 60502-1, CEI 60502-2, CEI 60840, CEI 62067, Che cavolo 6622, and AS/NZS standards — suitable for direct burial, duct installation, cable tray, e applicazioni sottomarine.
All cables undergo 100% per-metre electrical testing in our in-house 500kV high-voltage laboratory before shipment. ISO 9001 certificato da allora 2007. Exporting to 60+ Paesi.