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Choosing Your Fibre Cable
4 March 2019
Fibre Optic
When you purchase a cut length of fibre cable from your distributor you will likely to be thinking about the basic features you require. Top of the list will be the fundamentals such as transmission performance and compatibility with your optics. This usually comes down to Multimode OM3 / OM4 or single mode OS2 depending on the transmission distance and data speeds required. 

Next will come fibre count which will include ‘lit’ circuits and dark fibre for future use.  The environmental features will also be important to specify such as sheath type (Internal or external), overall diameter and possibly crush resistance. The bend radius is usually of importance to the specifier. There needs to be flex in the cable to be able to change direction within the confines of the cable containment whether being installed on a cable tray or in an external duct. External cables with PE sheathing or armouring will be significantly less flexible and may need duct pits where they need to be pulled into a duct, terminated or change direction. Tensile strength, if being pulled into ducts will also be a factor to be reviewed.

If the cable is being installed internally, other choices may need to be made such as the flammability rating and construction of the cable. Tight-buffered cable construction tends to be used more frequently for cabling inside buildings because it can be used in both vertical and horizontal cable pathway without additional measures. It can also be easier to prep / terminate than gel-filled loose tube types. However, it is limited in core count usually to 24 fibres and tends to be more expensive than loose tube. Loose tube or Unitube is where the fibres are contained within a semi-rigid plastic gel-filled tube. More recently a dry tube version has been introduced which eliminates messy gel and reduces the weight. Care must be taken with loose tube cable types if installing in the vertical plane e.g. building backbone. Loops will need to be added at intervals (typically every other floor) to avoid the risk of fibres breaking under tension and to prevent the gel from moving. The CPR flammability rating of cables has now precluded the use of universal cables (Internal/external) which were always loose tube type previously.

With so many attributes it goes without saying that there is a wide variety of fibre cables to choose from overall.  Distributors generally stock fibre cable in 1km or 2 km drums which are very bulky so they may be selective as to which lines they keep in stock. This means that unless a customer can order a 2km drum and accept a long lead time, there may be no alternative but to select a cable that is not perfectly suited e.g. higher fibre count (and unnecessarily higher cost).  In the past, with internal/ external cables this was less of a problem but now that they are not an option, distributors must ideally stock both internal and external cables. Networks Centre has one of the largest selections of LAN fibre cables in stock in the UK so customers can usually order the fibre cable they need without compromise.

With so many variables for a buyer to consider, one could be forgiven for overlooking the physical properties of the bare fibre itself. Whilst fibre is quite forgiving of bending, there can be issues caused by exceeding the specified bend radius e.g. if a cable is kinked. This is called macro bending and introduces unwanted losses.  Bend-insensitive and bend tolerant fibre reduces this effect and therefore are more robust for handling and managing. Review of a manufacturer’s specification will reveal the specific type of fibre and whether it is bend insensitive.  All Leviton Multimode OM3 and OM4  fibres are Bend Insensitive as standard as specified by IEC 60973.  Single Mode OS2 fibre cable is also specified G657.A1 ( ITU-T, the Telecommunications recommendations body)  which is Bend Tolerant on their internal Dry Loose Tube CPR compliant cables as standard. Both Bend Tolerant and Bend Insensitive Fibres give far better bending properties than non-bend insensitive types. Importantly, they are also backward compatible with non-bend insensitive fibres.

There are many reasons to choose to buy Leviton fibre cable from Networks Centre. Our extensive stock of 97 different types of fibre cable coupled with the superior specification are just two good reasons. The next time you need fibre cable call Networks Centre. We are fibre specialists and can provide advice to help you make the right choice.