Choosing The Right Optical Fiber Cable

While the same optical cable fiber may be used for many different applications, this is not the case for complete cables. The cable construction has to protect the fibers from many external factors such as the fibers from many external factors such as crushing forces, pulling forces, abrasion, corrosion and ageing, without any reduction in transmission performance of the fibers.

The fiber itself is sensitive to tensile forces and bending. The main purpose of the cable design is to protect the fiber during manufacturing, installation and operation. Critical parameters of the fiber such as service life and attenuation might suffer if the fiber is subjected to high external forces. There are two ways of coping with this problem. Firstly, the quality assurance system established at OPCOM Cables guarantees that only the right quality fibers are selected for production of cable. Secondly, the complete cable must be engineered and designed in an economical way to fulfill the demands imposed by the installation method and application.

When deciding on which cable design to choose for a particular application, a number of aspects must be taken into consideration. The following important points briefly describe these aspects.

Industrial standards
It is important that the cable complies with industrial standards for optical fiber cables, such as ITU-T (International Telecommunication Union-Telecommunication standardization sector) and IEC (International Electrotechnical Commission) to ensure quality and consistency. All OPCOM optical fiber cables are tested in accordance with these standards.

Transmission performance
When determining the transmission performance of the fiber, the fiber losses and the bandwidth of the transmission requirements should be taken into account. The performance should be chosen to meet the most stringent application for the location. The transmission performance should be stated for the cable and not the fiber.

Ease of handling and installation
The cable flexibility, colour coding, weight, resistance to bending, crushing and pulling forces make handling and installation quicker and more reliable.

Splicing and termination
Easily read cable and fiber identification makes splicing and termination easier and more accurate. The outer protection sheaths and coating should be easy to remove. The cutting of the fiber and the alignment of the fibers and cable is another important point to consider, as is the protection of the splice area.

Easy to repair
Easily read cable and fiber identification facilitates quick repairs and therefore shorter downtimes.

Environmental characteristics
The cable must meet the required performance in specific climatic conditions when installed. When considering the right cable design for a specific application, the demands the environment places on the cable must be taken into account.

For aerial cables, the span-width between the poles must be considered when choosing the strength member. Sometimes it can be more economical to have a stronger strength member increase the distance between poles. The cable resistance to wind-induced vibration is an important factor to consider as is the cable's ability to withstand ice loads in cold climates.

The environmental effect of an optical fiber cable is very small. To even minimize it further, OPCOM Cables avoids materials that may have a detrimental effect on the environment.

Water protection
Any cable may suffer damage, even if sheathed with the best design and quality material. When placed underground or in wet ambience, water and moisture may seep into the cable through the slightest sheath defects, thus causing damage to the cable. Sheath joints, if improperly attached may cause water to leak into the cable. Over an extended period, water vapour and moisture may even diffuse through a perfect plastic sheath.

When water enters a cable with a void between the cable elements, it can permeate along the cable core and accumulate at the lowest points of the cable network buried underground. This will reduce the lifetime of the fiber due to corrosion. There is also the risk of increased attenuation due to the high content of hydrogen in the cable.

There are two ways of preventing water penetration into a cable. One way is to fill all the interstices between the optical fibers, ribbons, loose tubes and the sheath with a water-resistant compound. Examples of such filling compounds are thixotropic gel and petroleum jelly. Another method is by using a water swellable tape wrapped around the cable core.

These materials are known for their outstanding performance and are specially developed for this purpose. They prevent water penetrating along the cable length, thereby eliminating any problems or limiting them to the point of damage.

The filling compounds used in OPCOM optical fiber cables do not flow or drip from open cable ends at temperatures normally encountered during cable installations. On the other hand they remain soft at low temperatures and do not interfere with the movements of the optical fibers or the flexibility of the cable.

For indoor cables and cables for short distance installation as in "city networks", water protection using swellable tape is recommended. Cables with swellable tape are called "dry cable".

Fire resistance
Selecting good flame resistance materials can prevent the spreading of fire along a cable. PVC is fireproof, i.e. fire does not propagate along a PVC sheathing after ignition. PVC grades used for sheaths contain special additives which impart flame-retardant properties (FR sheaths). These additives do not affect the other properties of the sheath compound.

All indoor cables are tested under fire conditions according to IEC-60332.

Ageing and resistance to chemical reaction
Other characteristic to consider when choosing the most suitable cable is the cable's resistance to ageing. The normal expected service life of a cable is 40 years. However, the environment can affect this, for example, by exposing the cable to strong sunlight or oil spillage. If the materials used in the cable are not chosen with these factors in mind, the service life may shorten. All the materials used in the cables manufactured by OPCOM Cables have excellent properties against premature ageing.

Comments on the cable data presented
All values are typical and may be varied, in specific cases, according to customer demands.