By Chris Gemme and Rick Dvorak
Thousands of miles of high-density polyethylene (HDPE) communications conduit is installed every year. While deploying conduit is part of almost every cabling project, there is an important reason to deploy this protection. In addition to providing a permanent reusable pathway for future upgrades and repairs, conduit provides supplemental protection for valuable fiber optic cables. Fiber optic transmission cables are now an important part of everyday life. As technology advances, so does the need for increased bandwidth to support streaming video, online gaming and smartphone apps. Only fiber fed facilities can provide this bandwidth.
These advancements are driving broadband and cable operators to make major changes to their architectures. While their current architectures may be different, they all have one constant theme-push fiber deeper. While their drive is to push fiber deeper into their networks, conduit gives them peace of mind that their subscribers’ communications will not be interrupted by a cut fiber. How do operators push fiber deeper without incurring the expense of costly excavation to install more conduit? The answer is microtechnology.
Standard conduit sizes range from a 1-inch nominal diameter to a 6-inch diameter. Installation methods include opening a continuous trench and placing the conduit into it, horizontal directional drilling or boring, installing plow chute and pulling innerduct into larger existing conduit, such as between manholes, handholes or buildings. Conduit provides a permanently protected pathway for communication cables, whether they are copper, coaxial or fiber optic. The cost of building and/or reconstructing a network creates the biggest challenge. Operators are challenged to not only answer current needs, but also to plan for future needs. Because of their smaller diameters, microducts reduce right of way requirements for building such pathways, as well as saving on installation costs and rapid deployment. By creating a permanent HDPE microduct pathway, cables may be economically installed, removed or upgraded as needed with minimal disturbance to soil, rights of way, shrubbery, walkways or roadways.
What is a Microduct?
Microducts are small conduits that are suitable pathways for housing microcables and can be considered suitable replacements for larger conduit structures. Microduct sizes range from 8.5/6.0 mm to 22/16 mm (Outside Diameter [OD]/Inside Diameter [ID]). For proper deployment, one needs to select the cable type, determine the cable’s OD and select the microduct size based on fill ratio and possible future cable requirements. Microducts can be used in fiber-to-the-home (FTTH), fiber-to-the-business (FTTB), longhaul, backhaul, premise fiber deployments and nearly any location where traditional conduit installations occur.
Bundled microducts further expand the flexibility and total fiber capacity in any installation. Single microducts can be factory pre-installed with coaxial cable or fiber in a single conduit. They may also be pushed into existing conduits already in place. One microduct allows an operator to deploy up to 144 fibers or greater, while deploying additional microducts will provide additional pathways for future expansion. Each microduct can be coupled at various locations, allowing operators to jet cables at distances of thousands of feet in a single operation, while also minimizing splice points.
Microcables are made with the same glass as conventional single mode fiber cables and provide the exact same performance for the signal. Microcables provide enhanced fiber installation methods for efficiency and ease of handling. The new smaller cables can be jetted (air blown) at speeds exceeding 200 feet per minute, shortening deployment times, which equates to saving on capital and operational expenditures. These smaller cables also allow for smaller enclosures, enabling operators to place them in most existing vaults and pedestals, again saving time and money. New handholes can be smaller and placed at greater intervals for further cost savings.
What is Jetting Fiber?
Air is used as a means to reduce friction between the microfiber cable jacket and the inside wall of the microduct. There are two types of friction that must be overcome by the microfiber to efficiently move forward-static friction and dynamic friction. Static friction is the force that exists between the contact surfaces when an object is not in motion. It tells operators how much force is needed to start that object in motion. Dynamic friction is the force that exists between the contact surfaces when an object is in motion. It tells operators how much applied force is needed to keep the object in motion. The heavier the object is, the greater the friction is. Air pressure (bars or pounds per square inch [PSI]) is more critical than volume of air, which is typically referred to in cubic feet per minute (CFM). So, 15 bars (217 PSI) at 35 CFM is the ideal and maximum pressure that should be used, while 10 bars (145 PSI) at 180 CFM of pressure is the minimum. The greater the air pressure, the less tendency the surface of the microfiber will come in contact with the surface of the microduct.
To reduce weight and OD, the strength members and sheath design of microcables are modified to result in a smaller form factor while providing the same fiber strand capacity. Microcables are generally jetted inside a microduct. Overrides with microducts increase the capacity of existing empty or occupied conduit structures. The use of these smaller ducts and cables for communications and data solutions is generically referred to as microtechnology. Microtechnology is widely accepted in North America as an alternative to traditional cabling solutions.
The scope of a project and volume of work will dictate an operator’s jetting equipment needs. There may be little need to equip more than one or two crews with jetting equipment for a large system or possibly even a region. Jetting equipment suppliers can help match operators’ equipment performance and volume requirements to fit their demand.
While microducts are generally considered outside plant products, there are versions available for use inside buildings made of fire-resistant materials. Microducts deployed in an enterprise setting can be used effectively in various applications-from aerial to direct buried, horizontally directionally drilled (bored), plowed-in or pulled into new or existing underground conduit systems. They can also be placed into rack systems, pulled into rigid steel conduit or used as a stand-alone system in walls, ceilings or foundations.
Operators are at a point where they wish they had placed more conduit in the ground or added a higher fiber count the first time in specific installations. The reality is that no one can accurately predict the future. Throwing large amounts of conduit and fiber in the ground for the future is not a sound financial strategy. There must be a compromise. The North American market is primed to take advantage of microduct and microcables in the outside plant, extending bandwidth capabilities in a scalable approach. Microduct and microcables afford the compromise of cost savings now vs. future needs.
About the authors: Chris Gemme, CommScope: Chris Gemme is manager of global technical services, Broadband, for CommScope, a global provider of communications networks and infrastructure solutions. Gemme has more than 20 years experience in telecommunications. Prior to his current role, he served as an applications engineer and as product manager of coaxial cables. Before joining CommScope, he worked at Time Warner Cable. Gemme earned his BS degree from Troy State University and his MS in business administration at Regis University.
About the authors: Rick Dvorak, Dura-Line: Rick Dvorak has been with Dura-Line since 2008 as an Application Engineer, and prior to that on AT&T’s Technical Evaluation Team, BellSouth Construction Staff, and a total of more than 42 years in OSP experience.