I. A Frequently Underestimated Selection Issue

In cable selection, one question arises frequently but is rarely taken seriously:

"Do I need armor?"

Many overseas customers, when inquiring about prices, either assume armor is required outright—"Adding a steel strip is better than nothing"—or completely disregard armor—"The cable is buried in the conduit anyway."

Both extremes can lead to problems.

If armor is not added when it's needed, the cable may be chewed through by rats, damaged by stones, or strained during installation after a few months of operation. Adding armor when it's not needed not only increases unnecessary costs—armor typically accounts for 15% to 25% of the total cable cost—but also increases the cable's rigidity and weight, making installation more difficult.

So, when should armored cables be used? And when can they be omitted?

II. The Core Function of Armor: More Than Just "Pressure Resistance"

Many people associate armor with "pressure resistance." However, armor provides multifaceted protection.

First, compression and impact protection.

This is the most obvious function of armor. The steel tape or wire armor layer can disperse externally applied point pressure, preventing localized forces from concentrating on the insulation layer. When the cable is buried directly underground, the armor can effectively withstand soil pressure from above, occasional passing light vehicles, or accidental impacts during construction.

Second, enhanced tensile strength.

For steel wire armor (SWA), it not only resists compression but also withstands considerable axial tensile force. This makes steel wire armored cables ideal for vertical installations—such as extending from the electrical room of a high-rise building to various floors, or hanging on overhead supports. Steel tape armor (STA) has weaker tensile strength and is mainly designed for compression applications.

Third, rodent and termite protection.

This is a particularly important but often overlooked function in tropical and subtropical regions.

Ordinary PVC outer sheaths are like soft cheese to rodents (rats, squirrels) and termites. Rats can gnaw through a standard sheath within hours, directly accessing the insulation. Once the insulation is damaged, a short circuit is inevitable.

Steel tape or wire armor acts as a physical barrier. Rats and termites cannot gnaw through the metal. In termite-infested areas such as the Middle East, Southeast Asia, and Africa, armor is almost standard on underground cables.

Fourth, the "last line of defense" after outer sheath damage.

Even if the outer sheath is accidentally scratched during installation or operation, the armor can still temporarily prevent moisture and contaminants from directly contacting the insulation. This provides a window of opportunity for inspection and repair.

III. When Armor Must Be Considered.

According to international engineering practice and the requirements of IEC 60364, armored cables should be prioritized in the following scenarios:

Scenario 1: Direct Burial. When cables are directly buried in the soil without conduit or sand protection, armor is the recommended configuration.

The soil may contain stones, construction debris, or even sharp objects discarded by humans. Over time, freeze-thaw cycles and subsidence alter the stress environment around cables. The armor layer protects against these long-term mechanical stresses.

Furthermore, once buried cables are installed, excavation and repair costs are extremely high. Adding an armor layer is like buying "prevention insurance."

Scenario Two: Areas with Potential Rodent or Termite Infestations

This is listed as a "recommended condition" in many technical specifications, but in practice, it should be considered a "necessary condition" in many areas.

If your project is located in an area known to have termite activity—such as around rainforests or underground pipe networks in old urban areas—or if site staff have reported rodent infestations, then not adding armor is tantamount to taking a known risk.

A case from a Middle Eastern project illustrates this: a batch of directly buried armored cables and a batch of unarmored control cables were laid on the same route. Two years later, multiple short-circuit faults occurred in the unarmored control cables. Upon excavation and inspection, dense rodent bite marks were found on the outer sheath. The armored cables, however, remained intact.

Scenario 3: Vertical Laying or Laying with Large Drops

When cables need to be laid vertically along shafts or cable trays, or on terrain with significant slopes, the cable's own weight will generate continuous axial tensile force.

In this situation, wire armor (SWA) should be chosen instead of steel tape armor (STA). Wire armor can withstand axial tensile force, while steel tape armor is prone to "coiling" or "detaching" under tension.

In high-rise buildings, vertical cables extending from the basement distribution room to more than 20 floors, without wire armor, may cause the copper conductor to thin and the insulation layer to become thinner over time due to the cable's own weight.

Scenario 4: Environments with Potential Chemical or Electrolytic Corrosion

In some industrial environments, such as chemical plants, sewage treatment plants, and areas near DC traction systems, cables may face the risk of chemical corrosion or stray current corrosion.

PVC outer sheaths offer some resistance to chemical corrosion, but are not foolproof. Armor layers (especially galvanized steel tape or wire) provide an additional barrier. For highly corrosive environments, non-metallic armor (such as fiberglass tape) or stainless steel armor can be chosen.

Scenario 5: Applications Requiring Electromagnetic Shielding

While armor layers are not specifically designed for electromagnetic shielding, metallic armor does provide a degree of shielding.

For control cables or instrument cables laid near strong interference sources such as large variable frequency motors, welding equipment, and high-power rectifiers, using armor layers can help reduce electromagnetic interference. For these applications, wire armor typically provides better shielding than steel tape armor.

IV. When Armor Can Be Delayed

Not all projects require armor. In the following scenarios, unarmored cables may be a more reasonable choice.

Scenario 1: Cables Run Through Conduit (Conduit Protection)

If the cable is laid in a sufficiently strong metal or PVC conduit, and the conduit is properly installed (no sharp bends, no damage), then the conduit itself provides mechanical protection, making armor redundant.

However, it should be noted that the effectiveness of conduit protection depends on the integrity of the conduit and the quality of installation. If the conduit has loose joints, is damaged, or flattened by stones, the protective effect will be greatly reduced.

Scenario 2: Cable Tray or Cable Tray Installation

In indoor environments, cables are laid in covered metal cable trays or cable troughs, which provide sufficient mechanical protection. In this case, unarmored cables can be chosen to reduce costs and installation difficulty.

However, there is an exception: if there are a large number of cables in the tray, the weight of the upper cables may compress the lower cables. In this case, it is still recommended to armor the bottom few cables.

Scenario 3: Aerial Installation

When cables are suspended from steel strands or overhead supports, the cables themselves are not subjected to external mechanical pressure and do not require compression protection. Aerial cables are typically unarmored to reduce their weight and wind load.

Scenario 4: Dry Indoor Environment

In dry, enclosed indoor environments such as power distribution rooms, control rooms, and computer rooms, free from rodents, cables are typically laid in cable trays, cable ducts, or conduits, and are regularly inspected. The risk of mechanical damage is very low, and unarmored cables are sufficient.

V. Steel Tape Armor vs. Steel Wire Armor: How to Choose

Many customers know they need armor, but are unsure whether to choose steel tape (STA) or steel wire (SWA). These two have significantly different uses.

Steel Tape Armor: Steel tape armor consists of two layers of galvanized steel tape spirally wrapped together, primarily providing compressive strength protection. It is suitable for direct burial, conduit, and cable tray installations where axial tensile forces are not required.

Steel tape armor has a relatively small bending radius, offering better installation flexibility. However, it performs poorly under axial tensile forces—the steel tape can undergo plastic deformation or even detach under tension.

Steel Wire Armor: Steel wire armor consists of one or more layers of galvanized steel wire spirally wrapped together, providing both compressive and tensile strength protection.

Steel wire armor is suitable for vertical laying, laying with large drops, or scenarios requiring tensile strength. It offers higher mechanical strength, but is also more expensive, has a larger bending radius, and increases laying difficulty.

Quick Selection Guide: If you only need protection from stones and rodents during direct burial, steel tape armor is sufficient.

If your cable needs to be laid vertically upwards for more than 20 meters, or if there is significant tensile force along the laying path, you must choose steel wire armor.

VI. A Common Misconception about Armored Cables

Some engineers believe, "With armor, the cable will never break."

This is incorrect.

The armor layer only provides mechanical protection; it does not solve electrical problems. If your cable has incorrect selection (insufficient current carrying capacity), installation problems (too small bending radius), or environmental issues (long-term immersion in water, chemical corrosion), the armor layer will not help.

Furthermore, the armor itself can also have problems.

In humid environments, steel tape or steel wire armor will still rust if the galvanized layer is of poor quality or scratched during use. Corroded armor expands, exerting inward pressure on the outer sheath, eventually causing it to crack and allowing moisture to enter the cable.

Therefore, when selecting armored cables, don't just look at whether they are armored; also pay attention to whether the armor material, galvanizing quality, and thickness meet the requirements of the operating environment.

VII. Summary: A Simple Decision-Making Framework

When you need to determine whether a cable should be armored, ask yourself the following questions in order:

First, in what environment will the cable be laid?

If directly buried, with rodent/termite risks, or potentially subject to mechanical impact, armoring is recommended.

Second, are there vertical sections or significant drops in the laying path?

If the cable needs to travel a long distance upwards, armoring is recommended, and it must be steel wire armor.

Third, are there other forms of mechanical protection?

If the cable is entirely within a high-strength metal conduit or in a covered cable tray, armoring may not be necessary.

Fourth, how do you weigh the costs and risks? Armoring increases costs by 15% to 25%, but it reduces downtime and maintenance risks due to mechanical damage. In critical routes or situations where maintenance is difficult, this is usually a worthwhile investment.

If you are still unsure, please send me a simplified diagram of the laying path and the site conditions. After reviewing the drawings and photos, I can provide more specific suggestions.