Benefits and constraints of FTTH rollouts using figure-8 cables
The figure-8 telecommunications cables are self-supporting cables. They represent a cost-effective and easy to install overhead solution, while also offering stable performances in a large range of operating temperatures. These cables are built with a messenger (steel or dielectric) and an optical fiber or copper cable core, both of them protected by a sheath forming a Figure 8 cross-section. The upper part of the figure 8 cable that serves as messenger wire is designed to withstand mechanical and environmental loads to which the cable will be exposed once installed (frost, snow, wind, …).
Cable manufacturers define the allowable tensile force depending on the span and the temperature range in which the cable can be used. This tensile force can register lower values for the span rolled out between the last pole and the anchoring point placed outside the building to be connected. Thus, telecom installers must pay a special attention to this one in order to guarantee the respect of the minimum bend radius during the deployment of fiber optic networks.
How to install figure-8 overhead insulated cables ?
An overhead line always starts with an anchor on the first pole used for this matter. The cable is then uplifted and maintained onto the next pole with the use of a suspension device. The operation continues up to the fifth pole, at most, where a second anchor will be installed. However, cables can be anchored as many times as considered to be necessary, especially when the figure-8 cable installation involves a road crossing, rugged terrain network configuration or any other relevant situation.
In case of dead-ending applications performed on figure-8 overhead lines, when clamping, the jaws of the figure-8 clamp puncture the messenger insulator and anchor on the steel part. However, for the roll-out of fiber optic figure-8 cables, the messenger’s sheath must remain unaltered. Dead-ending or suspension of figure-8 cables must therefore be carried out without damaging the insulation of these cables.
Which cable clamp for figure-8 fastening applications ?
To ensure future-proof networks, the clamping of figure-8 cables must be carried out in accordance with the engineering rules established by the owners of the energy or the telecommunications networks on which the telecom lines will be rolled out. Thus, depending on the network configuration, the choice of an anchor clamp or a suspension device must also take into consideration:
- The technology used by the cable to be deployed (fiber optics or copper)
- The messenger type: steel or dielectric
- The maximum allowable range for the cable deployment
Other factors impacting the quality of the network such as climatic elements or tensile strength are also important to ensure reliable and future-proof networks.
Thus, for anchoring figure-8 cables with steel or dielectric messenger rolled out on distribution networks with maximum spans of 90 meters, compact anchor clamps are available. These clamps enable a cable clamping over a total length of 60mm as well as a maximum tensile strength of 200daN. For tensile strengths of up to 300daN, cable clamps with elongated body are more suitable solutions as they enable a cable clamping over 120mm.
Reinforced cable clamps are used for the dead-ending of aerial figure-8 cables or aerial figure-8 duct structures with FRP messenger. These anchor solutions offer very good mechanical performances as they resist to tensile loads of up to 750daN.
For the dead-ending of figure-8 cables with dielectric messenger rolled out on feeder or distribution networks with spans up to 180 meters, anchor clamps with aluminum body represent a relevant technological solution. Designed with a flexible bail of 500mm, these clamps offer up to 1200daN mechanical performances.
Dead-ending solutions for figure-8 copper cables
The dead-ending of figure-8 cables with steel messenger rolled out on overhead lines with spans up to 90 meters is carried out with compact clamps for figure-8 cables. When installing these clamps, their jaw comes perforate the messenger’s sheath so to reliably clamp onto the steel core of the cable. Automatic cable clamps are also available for performing simple dead-ending applications on figure-8 cables with steel messenger. These clamps are used for the maintenance of copper networks, as well as for setting up poles requiring the management of a bare wire.
For the termination of figure-8 copper cables or the stay wire used for the reinforcement of wooden or metal telecommunications poles, parallel groove clamps are the best solutions. Composed of two metal plates including 2 or 3 tightening bolts, depending on the model, parallel groove clamps enable simple and reliable anchoring applications.
Which suspension solution for aerial fiber optic figure-8 cables ?
The suspension of figure-8 cables is performed easily and reliably by using SC suspension devices. These pole hardware devices are both compatible with figure-8 fiber optic and coax cables with diameters 3-11mm, rolled out on access networks where spans do not exceed 90 meters.
Designed as universal suspension solutions, SC suspension devices install on all type of pole: wooden, metal or concrete. They are fuse devices: in case of abnormal vertical load (tree fall, car accident,…), SC suspensions free the
cable and prevent thus any damage that may be caused to the cable’s sheath or the optical fiber.
Depending on the chosen version, SC devices are engineered to enable an articulated suspension (SC37C and SC71C) or a fixed suspension (SC39B).