Fibre Optic Cable Specification

by Spring Ning FiberStore IN China

Tensile Strength

One of the goals in any optical fiber cable installation is to complete the installation with as little stress as possible to the fibers themselves. For this reason, all optical cables are provided with a carefully calculated tensile loading value which should never be surpassed. For optical fiber cables, the tensile strength is the value that represents the highest load that can be placed upon a cable before any damage occurs to the fibers or their optical characteristics. It is not the fiber optic cable breaking strength but a realistic allowable limit. Most manufacturers will specify two load values, installation and long term.

The installation maximum load will be a higher value than the long-term load. The installation or short term load is the load the cable can withstand during the actual installation process. It includes additional stresses caused by pulling cable through, over or around stationary objects such as ducts, corners and conduits. Many installers will carefully meter the force with which they are pulling the cable throughout the installation to avoid accidentally pulling on it too hard. After the cable has been installed it will be subject to lower loads. This value is referred to as the installed, long term, static or operating load.

The tensile strength of the cable will depend upon the cable construction, and the application for which it is designed. For example, FiberStore's outdoor cables are designed to be plowed directly into the ground and have an installation load rating of 600 ibs. Our duplex Interconnect Series cables which are typically used inside wiring closets have an installation load rating of 211 ibs. If you are ever concerned that you may be exceeding listed cable values or are not certain what they are, contact FiberStore.

Bend Radius

The minimum bend radius is the value determined by the fiber cable manufacturer to be the smallest bend a cable can withstand. Bending the fiber beyond recommended limits could cause an incresase in the fiber attenuation at those points. Sometimes straightening the cable out will improve performance, but the best policy is to not overbend the cable. Like tensile strength, there are two values associated with bend radius, installation and long term.

The installation bend radius, again the higher value, is the amount of bending the cable can withstand while under the load of installation. After the cable has been installed and the stress of being pulled is removed, the cable may actually be bent to a smaller radius. These outside plant cable mentioned earlier may have a minimum installation bend radius of 6.3" and long term bend radius of 4.2". The zipcord minimum bend radii are 1.8" and 1.2", for installation and long term, respectively.

There are several common handling mistakes that lead to cable bend radii being surpassed. One of the most frequent errors is pulling cable through conduit with too small of a bend radius. Similarly, cable must never be over-bent going through trays, between tray sections, or when making transitions between locations. Cables should be "swept" to prevent sharp bends or corners. Optical fiber cables are designed for extra flexibility in closets or work areas. Unfortunately, it is often tempting to bend the cables tightly over corners, to keep the cables closer to equipment. Bending cable over corners, sharp or not, can cause serious damage to the performance of the cable. Care must also be taken to prevent wrapping the cable tightly around itself to be stuffed behind walls at the user end. Cables should never be kinked or knotted.

Crush and Impact

Cable crush and impact are often listed but rarely understood details of optical fiber cables. They do, however, provide some legitimate guidelines for cable installation. Crush and impact are important not as laboratory guidelines but as they apply to real life installation situations. For example, according to Bellcore 409, an interconnect riser rated cable must withstand a compressive load of 200 N/cm with an average increase of attenuation of not more than 0.4 dB. This means that every centimeter (.3937") of cable length can tolerate 200 newtons (44.9 ibs.) of pressure. That translates to 114 ibs. per inch tolerable pressure.

Optical fiber cables can be run in the same duct or tray as much heavier power cable. It is desirable to avoid placing excessive crushing forces on the fiber cables, however, by limiting the 
amount of "crossovers" or placing the heavier cables to the side or beneath the fiber cables. Consider the fact that a cable may be supported by ½" rungs in a runway or tray. If numerous heavy cables are placed on top of a fiber cable a force or pressure is exerted on the fiber cable, pressing it into the rung, causing potential damage at that point. Moving or shifting already installed cables that have large weights on top of them greatly increases the chance of damaging the cables.

FiberStore provides a wide range of quality optical fiber cables with detailed specifications displayed for your convenient selecting. Per meter price of each fiber cable is flexible depending on the quantities of your order, making your cost of large order unexpected lower. If you want to know more about fiber optic cable cost or fibre optic cable specification, please visit our website.

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