Armored or unarmored optical cable: which one to choose?

Introduction: Two Classes of Optical Cables

Optical cable transmits data through glass or plastic fibers. Based on the presence of protective armor, it is divided into armored and non‑armored. Armored optical cable contains a layer of steel tape or wire; non‑armored has only polymer sheaths and possibly aramid yarns. This single design element determines whether the line can be laid in the ground, overhead, or only indoors.

Armored cable withstands ground pressure, protects against rodents, and resists mechanical damage. Non‑armored cable is lighter, more flexible, and cheaper, but is suitable for laying in cable ducts, inside buildings, in trays, and in conduits. The choice of a specific grade depends on the environment, distance, fiber count, and reliability requirements. Detailed information on optical cable types and fibers is provided in the article about optical cable.

Comparison Table: Armored vs. Non‑Armored

Construction and Protective Covers

Armored optical cable is built around a central strength member: a fiberglass‑reinforced plastic (FRP) rod or steel strand. Around it, modules containing fibers are placed, filled with hydrophobic gel. Over the lay‑up, an inner polyethylene sheath is applied, followed by armor made of corrugated steel tape or round galvanized steel wires. The outer layer is a high‑density polyethylene jacket that protects the metal from corrosion and UV radiation. This multilayer construction withstands crushing loads, shovel digging, impacts, and vibration.

Non‑armored cable is simpler: fibers in a buffer coating or modules, aramid yarns for tensile strength, and an outer sheath of LSZH for indoor use or polyethylene for outdoor use. It may contain an FRP rod inside, but that serves to prevent shrinkage, not to protect against external impacts. Non‑armored cable is lightweight, flexible, and quick to prepare, but requires careful handling during installation. If the route runs through protected ducts, excess armor is unnecessary. On which cable to choose for indoor and outdoor use, you can read in the article indoor or outdoor.

Mechanical Protection and Laying Conditions

The main difference becomes apparent in the ground. Armored cable is laid directly in a trench on a sand bedding, without additional pipes. The armor absorbs soil pressure, impacts from stones, and protects against rodents. Laying depth is from 0.8 to 1.2 metres. This method is cheaper and faster to implement than building a cable duct system. Armored cable is also suspended on overhead line poles when high resistance to wind loads and ice accretion is required.

Non‑armored cable cannot be laid in the ground: sharp stones will pierce the sheath, moisture will reach the fibers, and rodents will chew through it. It is laid only in cable ducts made of asbestos‑cement or polyethylene pipes, in trays, conduits, or along walls. Inside buildings where there are no mechanical risks, non‑armored cable is preferable: it takes up less space, does not require grounding of the armor, and is easier to terminate into cross‑connect equipment. For outdoor aerial installation without armor, self‑supporting optical cable with a dielectric strength member can be used, but its tensile strength is limited.

Flexibility, Weight, and Bending Radius

Armored cable is stiffer. Steel tape or wire increases the minimum bending radius to 20 outer diameters, whereas non‑armored allows a bending radius of 10 diameters. When installing in tight spaces, cabinets, and splice cassettes, the stiffness of armor creates inconveniences: it is harder to store slack, and more space is required. The weight of armored cable is two to three times higher, complicating transport and lifting to height. Non‑armored is lightweight, easily pulled through pipes, and simpler to splice.

Flexibility is especially important for indoor distribution with many bends. For data centers and offices, non‑armored cables with multimode 50/125 fiber and fiber counts of 4, 8, or 12 are used. For long‑haul trunk lines, armored cable with singlemode 9/125 fiber and fiber counts of 16, 24, or 48 is standard. A comparison of singlemode and multimode fibers is given in the article singlemode or multimode.

Application Areas: Ground, Ducts, Indoors

For laying in the ground, on open routes, in swampy areas, and under roads, armored cable with wire armor that can withstand tensile forces during pulling is chosen. In cable ducts, non‑armored cable with a polyethylene sheath is acceptable, but if there is a risk of rodent damage or silting, armored cable is used. Inside buildings, including vertical risers, non‑armored LSZH cable complies with fire safety regulations and is easy to install.

Aerial installation on poles is done with self‑supporting or armored cable. If the line runs along a railway, in a forest area, or in regions with heavy snow, armor protects against falling branches and ice. In municipal ducts, armored cable is often replaced with non‑armored in pipes to reduce costs. The choice of a specific type depends on the project and customer requirements.

When to Choose Armored Optical Cable

• Direct burial in the ground without duct systems.
• Routes with high risk of mechanical damage: construction sites, mine workings, road crossings.
• Overhead lines in forested areas where falling branches are possible.
• Facilities with rodent issues: grain storage, warehouses, basements.
• Long‑haul backbone lines where reliability is critical and repair is difficult.

When Non‑Armored Is Sufficient

• Installation inside buildings, in trays, conduits, above suspended ceilings.
• Cable ducts with protective pipes.
• Data centers and server rooms where many bends and flexibility are needed.
• Local area networks indoors over short distances.
• Budget‑constrained projects where there are no external mechanical threats.

Typical Mistakes in Selection

• Laying non‑armored cable in the ground without a pipe. The first soil pressure or rodent will take the line out of service.
• Using armored cable indoors unnecessarily. It is more expensive, heavier, harder to prepare, and may not meet fire safety standards due to the flammable polyethylene outer sheath.
• Ignoring grounding of the armor. The steel tape must be grounded; otherwise, static charge accumulates, posing a hazard to equipment and personnel.
• Bending armored cable with a radius smaller than allowed. The steel tape breaks, creating sharp edges that damage fibers.
• Skimping on armor in areas with potential ground movement. In a few years, expensive repairs will be required.
• Ordering non‑armored cable for overhead installation without a supporting messenger. The cable will sag and break under its own weight and wind.

Frequently Asked Questions

What is the difference between armored and non‑armored optical cable?

The presence of metal armor – steel tape or wire. It protects against mechanical damage and allows laying in the ground, but increases weight, stiffness, and cost.

Can non‑armored cable be used underground?

Only in protective pipes or cable ducts. Without protection, non‑armored cable is quickly damaged by stones, rodents, and moisture.

Which optical cable is better for outdoor use: armored or not?

For suspension on poles, armored is preferred due to wind loads and possible falling branches. For duct installation, non‑armored with a polyethylene sheath can be used.

How many fibers are typical in armored cable?

From 4 to 48 or more. The most common are 8, 16, 24 fibers for trunks. For local branches, 4 fibers are used.

Does armor affect the fiber type?

No, armored cable can contain both singlemode 9/125 and multimode 50/125 fibers. The armor protects regardless of the fiber type.

What is the service life of armored cable?

In the ground – 25–30 years, with proper installation and grounding. Non‑armored indoors lasts 20–25 years.

Conclusion

Armored and non‑armored optical cables are not interchangeable without assessing the conditions. Armored is mandatory for ground and hazardous areas; non‑armored is for indoor distribution and protected ducts. Overpaying for armor where it is not needed is pointless, and its absence in aggressive environments leads to failures. The correct choice is based on the laying environment, required flexibility, and budget. Compliance with regulations and standards ensures reliable operation of the optical line for decades.