Armored vs unarmored MV cable selection depends on the mechanical risk around the underground route, not only on voltage rating. Both designs can use XLPE insulation, 導体スクリーン, 断熱スクリーン, 金属スクリーン, and an outer sheath. The difference is the added armor layer, usually steel wire armor, スチールテープアーマー, アルミワイヤーアーマー, or another metallic protection layer designed to resist crushing, インパクト, pulling stress, and external damage.
For XWA Power & ケーブル, armor is specified when the route exposes the cable to mechanical stress that cannot be controlled by duct, 寝具, cover slab, 埋設深さ, or installation management alone. Unarmored MV cable remains valid when the route is protected by ducts, trays, controlled trenches, or indoor cable systems. The engineering task is to match construction to route risk, fault-current behavior, bending limits, とインストール方法.
The decision starts with route risk, not catalogue preference
Medium voltage cables are installed in many different underground conditions: direct burial in sand bedding, concrete cable trenches, ダクト, トンネル, 産業プラント, utility corridors, 採掘現場, renewable-energy substations, and public infrastructure routes. The same nominal voltage can face very different mechanical exposure. A protected concrete duct bank does not create the same risk as a rocky direct-burial route with future excavation activity.
Armor adds a physical barrier outside the cable core. It can improve resistance to crushing, インパクト, and accidental contact with soil pressure or installation tools. It can also make the cable larger, heavier, less flexible, and more demanding to pull. This is why armor is not a universal upgrade. It solves mechanical risk while creating handling, 曲げ, ボンディング, and cost consequences.
XWA normally reviews armor design together with MV電源ケーブル 工事, project voltage class, メタリックスクリーンの要件, シース材質, and factory testing. For voltage-specific project discussions such as 33kVケーブル, armor cannot be separated from short-circuit screen area, ケーブル直径, pulling route, and the installation plan.
Where armored MV cable makes engineering sense
Armored MV cable is generally suitable where the cable faces direct mechanical threat. Direct burial is the most common reason. Soil pressure, stones, construction activity, route crossing, vehicle load, and future excavation risk can justify an armor layer. Industrial sites also create mechanical hazards: moving equipment, heavy foundations, limited trench space, and possible contact with tools or structural edges.
Armor is also useful when route control is incomplete. A cable installed in a public utility corridor may be exposed to later civil work. A mining or heavy-industry route may face vibration and rough handling. A renewable-energy collection system may run across long outdoor trenches where consistent protection is difficult. In these cases, armor can reduce the probability that the sheath and insulation system are damaged by external force.
| ルート状況 | Armored MV cable relevance | Engineering note |
|---|---|---|
| 土壌への直接埋設 | Often preferred where mechanical exposure is high. | Bedding quality, 埋設深さ, warning tape, and cover slabs still matter. |
| Rocky or mixed backfill | Armor can reduce damage risk but does not replace proper bedding. | Sharp stones near the sheath should still be avoided. |
| Industrial plant route | Useful near equipment, foundations, and areas with future maintenance work. | Bending radius and pulling tension must be reviewed. |
| Duct bank or concrete trench | May be unnecessary if the duct provides reliable mechanical protection. | Thermal condition and pulling force may favor unarmored design. |
| Long single-core circuit | Armor material requires careful electromagnetic review. | Non-magnetic armor may be needed to control losses and heating. |
Where unarmored MV cable is the better engineering fit
Unarmored MV cable is not a weaker product by default. It is a cable designed for routes where external mechanical protection is handled by the installation system. In duct banks, cable tunnels, indoor trays, protected trenches, and controlled substation routes, an unarmored design can reduce diameter, 重さ, 引っ張る力, and bending difficulty. It can also simplify accessory preparation.
Unarmored design may be especially practical for long pulled runs through ducts. Lower diameter and weight reduce installation stress. A smoother outer sheath can move through ducts with less friction. When the duct, 寝具, and route protection are properly designed, adding armor may not improve the actual reliability of the route. It may instead increase pulling load and reduce installation margin.
The design choice therefore depends on the protection system around the cable. If the route already provides mechanical protection, the cable can focus on electrical performance, sheath suitability, 画面デザイン, thermal rating, and installation efficiency. If the route leaves the cable exposed, armor becomes more valuable.
Armor types used in MV power cable
Armor is not a single construction. The common forms include steel wire armor, スチールテープアーマー, アルミワイヤーアーマー, and sometimes corrugated metallic sheath or special armoring systems. The cable voltage, コア配置, magnetic behavior, pulling route, 曲げ半径, and regional specification decide which form is reasonable.
Steel wire armor is common for multi-core armored power cable because it provides strong mechanical protection and good tensile support. Steel tape armor is often used where radial mechanical protection is needed and the cable design supports it. Aluminum wire armor or non-magnetic armor is often considered for single-core AC cables because magnetic steel around a single-core AC conductor can create additional losses and heating. This point is critical for larger MV and HV circuits.
| 装甲の種類 | Typical role | Main limitation |
|---|---|---|
| Steel wire armor | Mechanical protection and tensile strength, often in multi-core cables. | Adds weight and can complicate bending and handling. |
| Steel tape armor | Radial protection for certain cable structures. | Less suitable where high tensile load or repeated flexing is expected. |
| Aluminum wire armor | Non-magnetic armor option for single-core AC circuits. | Higher material cost and specification-dependent availability. |
| Corrugated metallic sheath | Moisture barrier and mechanical protection in special designs. | More complex accessory, 曲げ, and corrosion-control requirements. |
Mechanical protection is only one part of underground reliability
Armor can protect against mechanical damage, but it does not correct poor route design. The trench still needs suitable bedding, thermal backfill where specified, adequate burial depth, warning tape, cover slabs when required, and controlled cable pulling. Incorrect backfill can damage both armored and unarmored cables. Excessive pulling tension or sidewall pressure can deform the cable during installation. Small bending radius can stress insulation, 画面, 鎧, and sheath.
Underground cable engineering also includes thermal performance. A heavily armored cable can have different heat-dissipation behavior from an unarmored design. Duct installation can reduce ampacity because surrounding air gaps and duct materials affect thermal resistance. Direct burial can provide good heat transfer if soil thermal resistivity is controlled, but poor soil or dry conditions can reduce rating. Armor should be evaluated together with ampacity, not only protection.
General cable laying method discussions, such as engineering summaries on underground cable laying methods, are useful for understanding why route, trench, ダクト, and protection conditions shape the cable construction decision. XWA adds the factory perspective by tying those route conditions to manufacturable MV cable layers and release documentation.
How armor affects electrical behavior
Armor sits outside the cable core, but it can still influence electrical behavior. In three-core MV cable, magnetic effects are often less severe because the phases are grouped together and magnetic fields tend to balance. In single-core AC cable, magnetic armor around each phase can create induced currents, losses, and heating. This is why single-core AC armored cables often require non-magnetic armor or a different protection method.
Armor also interacts with grounding. Metallic armor may need bonding depending on the cable design and system practice. The metallic screen has its own electrical role, and armor does not replace the screen. The insulation screen, 金属スクリーン, 鎧, and sheath each perform different functions. Confusing these layers can create a specification that looks protective but does not meet fault-current or grounding requirements.
This topic connects directly with XWA’s existing technical article on MV cable screen types and metallic shield design. The screen manages electric field and fault-current paths; armor manages mechanical exposure. Some cable designs allow the armor to participate in bonding, but the two functions should still be specified separately.
Installation trade-offs created by armor
Armored cable is stronger, but it is also harder to install. The added metallic layer increases cable diameter and mass. Larger diameter raises minimum bending radius. Higher weight increases pulling tension and support requirements. The cable drum may become heavier, and route handling may require more lifting capacity. These practical details influence manufacturing, パッキング, transport, and site installation.
Unarmored cable is easier to pull and terminate in many protected routes. It can reduce duct fill, improve handling, and simplify accessory preparation. しかし, it depends on the route protection system. If the duct cracks, if trench bedding is poor, or if future excavation is likely, unarmored cable may have less mechanical margin. The project risk moves from cable construction to civil protection.
| Factor | Armored MV cable | Unarmored MV cable |
|---|---|---|
| 機械的保護 | Higher resistance to external damage. | Depends on duct, トレイ, trench, or civil protection. |
| Weight and diameter | より高い, affecting drums and pulling load. | より低い, often easier for ducts and long pulls. |
| Bending radius | Usually larger due to increased diameter and armor stiffness. | Usually more flexible within the same voltage class. |
| Accessory preparation | Armor stripping and bonding may add work. | Simpler where no armor termination is required. |
| Cost structure | Higher material and transport cost. | Lower cable cost, but may require stronger route protection. |
| Best fit | 直葬, rough routes, industrial exposure. | Ducts, トンネル, protected trays, controlled trenches. |
Standards and project specifications
IEC 60502-2 is commonly used for extruded insulation power cables in the medium voltage range. It gives important construction and testing context, but a project specification often adds armor type, シース材質, fire performance, 防水要件, ドラムの長さ, and inspection documents. National utility specifications may also define preferred armor forms for direct-buried or duct-installed MV cable.
The standard reference should therefore be read with the project route drawings. A cable can be described as IEC 60502-2 type, but armor selection still needs route information. If the route calls for direct burial in a public corridor, a standard unarmored cable may not match the practical risk. If the route is a fully protected duct bank, a heavy armored cable may be unnecessary and difficult to pull.
Factory checks before confirming armored MV cable
When an armored MV design is specified, XWA reviews the cable construction from conductor to outer sheath. The armor layer must fit over the bedding or inner sheath without damaging underlying layers. The armor material, wire diameter or tape size, lay direction, カバレッジ, and outer sheath thickness must be controlled. The final cable also requires dimensional inspection, voltage testing, シース検査, and packing review.
Factory testing does not end at the armor layer. The cable still needs the same electrical discipline as unarmored MV cable. 導体抵抗, voltage withstand, partial discharge review where required, 画面の連続性, and document traceability remain important. Armor improves external protection; it does not reduce the need for electrical quality control.
Route data needed before final construction
A practical armored versus unarmored decision needs enough route data. XWA normally reviews these items before confirming the cable construction:
- 定格電圧, 導体材料, 導体サイズ, コア数, and insulation material.
- 設置方法: 直葬, duct bank, concrete trench, トンネル, トレイ, or mixed route.
- Mechanical exposure: soil type, stones, traffic load, 将来の発掘リスク, and industrial hazards.
- Required armor type, or the route reason for not using armor.
- Metallic screen area, 故障電流, clearing time, and grounding method.
- シース材質, 防水要件, flame-retardant or LSZH requirement if applicable.
- Pulling length, number of bends, duct size, sidewall pressure limit, および設置設備.
- ドラムの長さ, 梱包方法, delivery route, 保管状態, and test document list.
工学的な結論
Armored MV cable is appropriate when underground routes expose the cable to mechanical damage that civil protection alone cannot reliably control. Unarmored MV cable is appropriate when ducts, trenches, トンネル, trays, or protected routes already provide reliable mechanical protection and the installation benefits from lower diameter and weight.
The correct decision is not “armored is always better” or “unarmored is always cheaper.” The correct decision is a route-based construction choice. XWAパワー & Cable evaluates armor together with voltage class, 画面デザイン, 故障電流, 接地方法, route protection, pulling conditions, accessory preparation, テスト, and shipment documentation.
よくある質問
Is armored MV cable always required for underground installation?
いいえ. Underground routes can use armored or unarmored MV cable. Direct burial or rough routes often justify armor, while ducts, トンネル, and protected trenches may use unarmored cable when civil protection is reliable.
Does armor replace the metallic screen?
いいえ. The metallic screen controls the electric field and provides a defined electrical path. Armor provides mechanical protection. The two layers must be specified separately.
Can single-core MV cable use steel wire armor?
Single-core AC cable requires careful magnetic-loss review. Steel armor around a single-core AC conductor can create losses and heating, so non-magnetic armor or another protection method may be required.
Why can unarmored MV cable be easier to install?
Unarmored cable usually has lower weight, smaller diameter, and better flexibility. These features can reduce pulling load and bending difficulty in protected ducts or controlled routes.
What information decides armored versus unarmored construction?
The main information includes route type, mechanical exposure, duct or trench protection, 定格電圧, 導体サイズ, 画面領域, 故障電流, bending route, 引っ張り長さ, sheath requirement, and inspection documents.