Unlike metallic power or copper communication cables, fiber optic cables have a unique distinction of having lightweight. One reason for the light-weight is the lack of metallic elements in fiber optic cables. However, some application environments demand metallic protection of fiber optic cables. Anyway, the use of metals or the after effects due to the presence of metal elements does not influence the optical transmission directly.
By the way, armoring of fiber optic cable is done to provide extra mechanical protection, which a normal outer plastic sheath alone may not be able to provide. For example, a heavy piece of stone falling on the cable or heavy vehicle traffic along the installed cable route etc.
We can classify the Armoring of optical fiber cables into two broad categories such as,
– Tape Armoring
– Wire Armoring
As the name indicates, the tape armoring is done by a tape, either metallic or non-metallic. Wire armoring is carried out by using wires that are typically round in shape. Flat or trapezoidal wires are also applied around the fiber optical cables.
A tape has a flat structure. It has a width and thickness. Width depends on the diameter of the bottom core over which it will be wrapped. There are two ways to wrap the tape; Horizontally along the cable length or helically over the cable. Both the horizontal and helical applications of the tape are done with an overlap. Overlap means crossing over. Typically a 10 percent of the tape width is considered to be a good overlap value.
The tape can be plain or corrugated. A plain tape is helically or longitudinally applied, while the corrugated tape is longitudinally applied. Some environments require two layers of tape (double tape).
Alternatively, instead of providing overlap, the tapes can be sealed over the inner core/cable to provide complete sealing of the inner layers. Bitumen can also be applied.
In summary, Tape Armoring can be made in two ways;
– Longitudinal (Corrugated tape)
– Helical (Plain or Corrugated tape)
There are several types of materials used for armoring;
Metallic (Stainless steel, ECCS tape, Copper tape, Aluminum tape)
Non-Metallic (Glass tape)
Wire armoring is done by helical wrapping over the core/inner sheath in order to securely tighten the wires. Helical stranding or wrapping is done with a lay length. The length of the lay or pitch depends on the wire diameter and bottom core/cable diameter.
Wires could be flat or round or trapezoidal and the material could be metallic or non-metallic. Commonly used wires are metallic, while some environments demand the use of non-metallic wires.
Metallic wires: Steel wires, Zinc coated GI wires, Copper or Aluminum wires
Non-metallic: Glass FRP or Kevlar FRP wires
Wire armoring is often done in combination with other protective layers such as plastic ropes or jute in order to provide additional protection against moisture or corrosion.
Applying a thick layer of glass yarns is also sometimes referred to as armoring. After all, Armoring is the method of protecting the inner layers same as the armors used by the warriors during the war.