Fibre cable Selection
Fibre Cable Selection Criteria
Selection of the right cable for the applicable environment is the key to long term survival of the cable. Several factors come into play when deciding which cable is best suited to your particular application.
For outdoor, loose tube constructions are preferred. These cables are typically stronger and more robust than their indoor counter parts. Tight buffered designs are preferred for indoor applications due to their lighter weight, smaller diameter and improved flexibility which makes them easier to install in tight spaces.
Garland Tight Buffered (GTB series) cables meet the AS/CA S-008 requirements for an outdoor cable. However, they must be protected from physical attack and excessive exposure to the environment.
Termites are a major problem throughout Australia. Used for over 40 years and accepted as the standard method of termite protection, the use of Nylon 12 as a termite barrier has been proven time and time again and is the method recommended by Garland.
Rodents such as mice, rats and some marsupials can also attack a cable. Rodent protection is normally in the form an armour or barrier.
Corrugated Steel Tape Armours (CSTA) offer the most secure option to resist rodent attack, as the rodent is unable to penetrate the steel tape. Steel tapes used by Garland also have an electrolytic chrome coating to help prevent rusting.
Where optical fibre cables are laid close to power cabling, the use a non-metallic armouring is preferred. This eliminates the risk of voltages being induced in the armour.
For areas with a low incidence of rodent attack, glass yarns may supply sufficient rodent resistance. Glass yarns add no additional mechanical strength, but rodents don’t like to chew it. When higher incidence of rodent attack is suspected, FRP rods are laid around the cable to provide both mechanical and rodent protection. However, neither type of non-metallic rodent protection offers security over several generations. This may result in an eventual breakthrough of the rodent barrier.
For indoor applications, it is a requirement of AS/CA S-008 that a flame retardant cable be used. In such applications a PVC or LSZH jacket is required. The use of PVC for cable jackets is on the decline due to the toxic and corrosive gases generated when PVC is burned. As a result, Garland uses Low Smoke Zero Halogen materials for the jackets on its indoor cables thereby meeting the flame retardancy requirements but without the risks associated with PVC under fire conditions.
UV present in sunlight can degrade the plastic used for jacketing optical fibre cables. To help address this, various UV stabilisers and blockers are added to the jacket compounds used in Garland optical fibre cables.
For fibre cable selection when installed underground, the cables can often sit in conduits, channels or ducts that can become filled with water. Over time, and when cable has been damaged by pests, this water can permeate into the cable effecting its performance. This can provide a path for water to travel along the cable and enter the cable termination equipment at the end.
For loose tube cables, jelly is injected into the tube along with the fibres to prevent water coming into direct contact with the fibres and to block the tubes. In between the tubes, water swelling compounds are applied. These expand when in contact with water providing a barrier to water traveling along the cable. Similar water swelling compounds are also used in the tight buffer cable constructions.