2.2 Specialty Cables

2.2 Specialty Cables

Standard tight-buffered and loose-tube cables cover the vast majority of local area networks and outside plant trunks. However, many fiber optic installations encounter challenging physical environments—such as high-density conduits, rodent infestations, high-voltage power lines, or deep-sea crossings. To address these scenarios, manufacturers produce specialty cables engineered with distinct structural layouts, strength members, and armoring.

Specialty Cables Comparison Table

Ribbon Cables

In applications demanding extreme fiber density within limited conduit space, such as metropolitan backbones and modern hyper-scale data centers, ribbon cables are the preferred solution.

Design and Construction

In a ribbon cable, up to 12 (or sometimes 24) optical fibers with 250 µm acrylate coatings are aligned side-by-side in a precise parallel plane. They are bonded together using a UV-curable acrylate adhesive matrix to form a flat, flexible ribbon. Multiple ribbons can be stacked on top of each other inside a single buffer tube or a central core. This stacked ribbon configuration allows manufacturers to pack thousands of fibers into a cable with a remarkably small outer diameter. For example, a single ribbon cable can house 3,456 or even 6,912 fibers.

Mass Fusion Splicing

The primary mechanical advantage of ribbon cable is its compatibility with mass fusion splicing. Instead of stripping, cleaving, and splicing each fiber individually—which is extremely time-consuming for high-fiber-count cables—a technician can prepare and splice all 12 fibers in a ribbon simultaneously. A mass fusion splicer uses a wide heating element to fuse all 12 pairs of fibers in a single electrical arc cycle. This reduces splicing labor times by up to 80% to 90%, turning a multi-hour splicing task into a process that takes just a few minutes.

Drawbacks

Ribbon cables exhibit preferential bending; they bend easily along their flat axis but resist bending along their edge. This makes them stiffer and harder to route through tight, multi-directional bends than circular loose-tube cables. Additionally, separating a single fiber from a ribbon for individual routing requires specialized ribbon-splitting tools to prevent damaging the fiber coating.

Armored Cables

For installations where cables are buried directly in the ground or routed through spaces prone to mechanical damage, armored cables are required.

Construction and Mechanical Protection

Armored cables contain a protective metallic sheath—typically corrugated steel tape or aluminum—located between the inner jacket and the outer polyethylene (PE) jacket. The metallic armor provides high crush resistance, protecting the optical fibers from heavy vehicle loads, soil settlement, and shifting rocks.

Furthermore, armored cables are the standard defense against rodent damage. Squirrels, gophers, and rats have a natural urge to chew on plastic cable jackets. Standard fiber jackets are easily pierced, but metallic armor stops rodents from chewing through to the delicate glass core.

Grounding and Bonding Requirements

Because the metallic armor is a electrical conductor, it can carry hazardous electrical currents. These currents may result from lightning strikes, static accumulation, or accidental contact with nearby power cables. Under the National Electrical Code (NEC) Article 770, all conductive components of a fiber optic cable—including metallic armor and steel strength members—must be electrically bonded and connected to an approved grounding electrode system at the point of building entry. Failure to ground armored cables poses a severe shock hazard to technicians and can damage network hardware during lightning surges.

Aerial Cables

Aerial installations involve suspending fiber optic cables from utility poles. These cables must withstand mechanical tension from their own weight, wind loads, and ice accumulation.

Figure-8 Cables

Figure-8 cables incorporate a built-in galvanized steel messenger wire running parallel to the fiber optic cable bundle, all enclosed within a single, continuous outer polyethylene jacket. When viewed in cross-section, the cable resembles the number '8.' The steel messenger wire bears all the mechanical tension of the span between poles, preventing any tensile stress from reaching the buffer tubes or optical fibers.

All-Dielectric Self-Supporting (ADSS) Cables

In environments where conductive steel wires cannot be used—such as on high-voltage power utility transmission poles—All-Dielectric Self-Supporting (ADSS) cables are utilized. ADSS cables contain zero metal. Instead of a steel messenger, they rely on layers of high-strength aramid yarns (such as Kevlar) wrapped helically around the inner buffer tubes to provide the necessary tensile strength.

Because they are fully dielectric (non-conductive), ADSS cables do not require grounding. They can be safely installed in the 'power space' at the top of utility poles, where high electromagnetic fields would induce dangerous currents in metallic wires, and they are immune to damage from lightning strikes.

Distribution vs. Breakout Cables

For indoor installations, two common multi-fiber tight-buffered configurations are distribution and breakout cables:

Distribution Cables

Distribution cables contain multiple 900 µm tight-buffered fibers bundled together under a single outer jacket, reinforced with aramid yarn strength members. The fibers share a common outer jacket and do not have individual jackets of their own. This makes distribution cables highly compact and lightweight, making them ideal for vertical riser shafts and horizontal backbone routing. However, because the individual 900 µm fibers are exposed once the outer jacket is stripped, they must be terminated inside a patch panel, wall outlet, or splice closure to protect the connection.

Breakout Cables

Breakout cables (sometimes called fan-out cables) are designed for rugged indoor environments. In a breakout cable, each individual 900 µm tight-buffered fiber is wrapped in its own aramid yarn strength member and enclosed in its own sub-jacket (typically 2.0 mm to 3.0 mm in diameter). All of these sub-cables are then bundled together under a heavy-duty outer jacket. While breakout cables are thicker, heavier, and more expensive than distribution cables, they allow individual fibers to be routed directly to equipment ports without the need for a patch panel or protective enclosure.

Submarine and Underwater Cables

Submarine cables are highly specialized, heavily armored assemblies laid across ocean floors to connect continents, or across riverbeds and lakes. These cables must withstand extreme hydrostatic pressure (exceeding 8,000 psi at ocean depths of several miles) and the corrosive effects of saltwater.

Construction

A submarine cable features a central optical core surrounded by a protective copper tube, which acts as a hermetic seal against water and hydrogen gas (which causes fiber darkening and attenuation). The copper tube also carries high-voltage direct current (up to several thousand volts) to power underwater optical repeaters (erbium-doped fiber amplifiers) spaced every 50 to 80 kilometers. Surrounding the core are multiple layers of high-tensile steel wire armor and a thick outer jacket of high-density polyethylene (HDPE). Near shorelines, where anchoring ships and commercial fishing nets pose a risk, submarine cables are extra-armored and buried in the seabed using specialized plows.