There have been two fundamental cable designs for the last couple of decades: Tight Buffered or Loose Tube.

Traditionally tight buffered would be seen as an internal design and loose tube an external design, there are exceptions, but it is a reasonable rule of thumb. Tight buffered is seen as easy and quick to install. The tight-buffered cables also had the appropriate sheath to conform to fire regulations prevailing at the time. In the early days, external cables were loose tube with a polyethene sheath, which was not acceptable for internal applications, fire regulations. This, coupled with Gel-filled tubes and interstices, made this cable design in-practical and costly for internal applications.

It is possible now to have a sheath on a loose tube that will conform to fire regulations. But there are practical difficulties with cable and fibre management that make the tight-buffered cable a far more efficient approach.

In this article, we will focus on Tight-Buffered cables and their applications.

Typical construction of a Tight-Buffered Fibre Cable

The basic construction of a 900u distribution cable or ODC Optical Distribution Cable consists of a number of fibres, strength & protection and an outer sheath. We generally see low fibre counts for ODC typical 4-24 fibre. It is possible to get higher fibre counts up to 144 fibre but not common in UK/Europe. The construction of any ODC starts with the Fibre 250u, which will be buffered to bring the diameter up to 900u. We have multiples of these with different coloured buffers or printed, giving each buffered fibre identity within the cable core.

The multiple buffered fibres form the core of the cable, where this is then surrounded by aramid yarns (Kevlar/Twaron or E Glass); this would normally be applied helically around the core. This would then pass into an extruder, where the sheath would be applied. Sheathing material will vary dependant on application and deployment; in UK/Europe, typically LSZH/ULSZH.


Diagrams 1 & 2 give a simplified view of the construction of a tight buffered Cable.

 

Typical Internal Applications of Tight Buffered ODC 

 

Having the right sheath specific for application is a legal requirement; understanding regulations is paramount when specifying cable sheaths for internal applications.
 

• CPR Construction Products Regulation 
• IEC 60794-1 / 60332-1-2 / 60331

Note. A detailed understanding of the above regulations is necessary before selecting a cable for a particular application. 

How to Select Tight-Buffered Fiber Distribution Cable

With a clear understanding of the technical specification and application you are now in a position to procure the cable. Tight buffered cables are available in a range of Fibre types, colours, counts, sheath type, colour and printing detail. 
 

1. First thing to consider is fibre type 

2. Application

3. Fibre Count 

Conclusion

TB cables are a mature product and have been available for many decades. As new fibre types come available OM4 & 5, then the TB range is refreshed, enabling the ability to service the high Bandwidth requirements. This particular product lends itself to inbuilding or campus environments. Linking floors or buildings, and relatively short distances. This product is also used extensively as a pre-terminated solution. However, this area of the market is now services by Pre-terminated solutions utilising MTP/MTO technology. We believe that TB cable will be with us for quite some time, but there is and will continue to see a steady migration to Pre Terminated MTP/MTO solutions.

CMW has a wealth of knowledge to help you specify the correct product for your project or a particular application. CMW also stock a comprehensive range of 900µ TB (Tight Buffered) cables, various fibre types, Fibre Counts & Sheaths. If your application is indoor, outdoor or Direct Burial.