Originally published by Sheri Dahlke in “Cabling Installation and Maintenance Magazine,” Oct 30, 2020 Issue. Reproduced with permission.
Best-practice measures help ensure your cable pull is as smooth and successful as possible.
Just one year ago, few of us would have guessed that our business practices would radically change to enable us to manage during a pandemic. While health professionals, epidemiologists, and perhaps movie directors may have envisioned the chaos of a highly infectious, deadly disease, our business plans were not developed based on this unforeseen event.
Although some of our plans have been upended, the planning process continues to help us navigate this “new reality.” Winston Churchill said, “Plans are of little importance, but planning is essential.”
Both history and experiences taught us that business planning improves our odds of success and reduces our chances of failure. Planning includes assessing the current state and preparing for future outcomes. This preparedness allows a faster response if things do not go as planned.
We do not plan to trip and fall while hiking. However, our packed first aid kit will help us return home safely. Planning allows us to protect our assets and to grow our retirement savings and investments.
In addition, planning can open the door to other opportunities, including cost savings. Consider when mapping a road trip that by researching multiple routes, we may discover the most efficient, safest, and most successful route, including a new stopping spot along the way.
Why do we skip planning? It takes time. Planning time is not lost time. Though it can be challenging, it is always worth the effort, because it gives us a sense of what is ahead, including obstacles and opportunities. A well-researched and considered plan can prevent chaos, squandered resources, and loss of money, particularly in projects where there is a major outlay of financial resources and materials.
Adjusting and adapting
In the event a situation changes, our plans need to change. If our tactics are outlined in the strategy, we can then implement them and adapt as conditions evolve.
Consider the example of fiber-optic cable projects. While fiber-optic cable is relatively robust, it can still be damaged. This damage may not be apparent until testing is done after the cable is installed. Fiber-optic cable is expensive, especially when adding labor costs. This is an instance where planning before the work is started prevents a “redo” and saves in replacement costs.
Following is a suggested beginning-to-end process from planning to cable installation.
Route survey and cabling plan
Create a detailed plan with pulling, intermediate assist points, and cable feed locations. A careful route survey is one of the first elements to complete. Consider elevation and offsets and determine optimum splice points.
Indoor installation: You will need to determine the type of building structure or environment and specific locations of running cable, such as under floors, in the ceiling or through conduit. In addition, determine the accessibility of the raceway.
External environments: Develop and review a comprehensive safety and Occupational Safety and Health Administration (OSHA) regulatory checklist to ensure that no components are omitted, from protections to traffic to maintenance hold ventilation.
Cable design and handling
Review cable specifications, as all fiber-optic cables have a maximum load or pull tension, which subjects them to being easily damaged by excessive pull, bend or crush. Ways to avoid the aforementioned damage are outlined in the steps that follow. Staying below this limit will avoid hidden damage that may surface only after the installation is complete.
Based on the maximum cable load, use a breakaway swivel, tension-limiting capstan, or other tension-monitoring equipment.
Attach pulling grips to the jacket, aramid fiber, and strength member to distribute the force. A swivel is a key piece of equipment. Use of a swivel between the pull line and grip keeps the cable from twisting.
Review the swivel breakaway load so that the cable tension limit is not exceeded. Even for hand-pulled cable, care must be taken so that pull tension limits are not exceeded.
• Crush strength is the ability of the fiber to withstand compression force. In cable pulling, it can also be described as the sidewall force.
• For fiber-optic cable, that is rarely the problem. If both the maximum pull tension and bend radius are observed, it is unlikely the crush strength will be reached.
• It is important not to stack material on top of the cable, including the large quantities of the cable itself. This is especially true if the weight of the material is not distributed through a long length of cable.
• Although some cables are designed to be crush-resistant, that does not mean that they are indestructible.
• Fiber optic cables have a minimum bend radius, typically specified as a multiplier of the outside diameter. Some cables are considered bend-insensitive. These cables are designed with a fundamental change to the glass chemistry and even these cables will have a minimum bend radius.
• Bend radius is found in the cable specification and determined by the cable manufacturer.
• Bending the cable past its limit during installation, or afterwards, may damage the fiber, resulting in attenuation.
• It is possible to break individual fibers without any visible physical damage. Be aware of and manage the bend radius when designing your raceway.
• Ensure lip rollers or quadrant blocks meet minimum bend radius requirements.
• Innerduct size should be chosen to allow for optimum cable fill ratio. High fill ratios tend to increase tension due to greater surface of rubbing.
• When bundles of cables are pulled, there is less shifting room, especially as the cables are pulled through a bend.
• Cable fill guidelines are dependent on cable number. This allows for proper clearance, which is a related factor that ensures cables will fit into the conduit.
• Innerduct type and the way it is laid or routed could also impact cable tension. Innerduct memory or helixing can increase pulling tension as it increases pulling bends.
• When splicing innerduct sections, do not use couplers. Using couplers could reduce the inner diameter or add a lip that may scrape the cable.
• Cap innerduct before the pull to keep it free of contaminant.
• Once the pull is started, keep tension and pulling rate steady.
• Most cable manufacturers recommend using cable lubricant that is compatible with the cable jacket and its use is viewed as the most effective way to lower tension (force), to keep the cable from sticking, kinking, and twisting during the run. This steadies the pull and effectively limits further damage.
• Many substances can be used as a cable lubricant. However, generic materials, such as liquid detergents, are more likely to be noncompatible and can hurt the cabling.
• Best practices for lubricating include pulling a lubricant swab through the innerduct to clear the route and pre-lubricate. Other methods include pouring a lubricant directly into the duct or coating the cable as it enters the conduit.
• Cable lubricants lower the coefficient of friction and make it more predictable.
• These values can predict tension and sidewall forces.
• Understanding the forces on the cable will optimize the design and prevent damage to the cable.
Good planning ensures successful cable pulling and can increase efficiency while decreasing outlay of resources. Plans help you optimize your project design and installation while preventing damage to cable, which is costly. We have provided some step-by-step guidance and technical best practices to help you prepare for each cable project, large or small.
Sheri Dahlke serves as technical director for Polywater, where she provides strategic leadership in product development and technical service. Her career spans more than 30 years with Polywater, during which she has led industry efforts in research and development, global regulatory requirements, and new product development particularly in adhesives, cleaners and lubricants used in the communications and electrical industries.