Fiber optic cable is strong, reliable and built for long-term performance, but it still needs to be handled correctly during installation. Most fiber damage does not come from normal operation after the system is live. It happens during installation, when excessive pulling force, tight bends, crushing or poor pathway planning place unnecessary stress on the cable.
The following article explores best practices when pulling fiber optic cables and cable assemblies. Following these guidelines will help protect your system's optical performance, reduce installation failures and extend the overall life of the network.
Cleerline also offers a short video that details cable pulling best practices.
Plan the Pull Before You Start
A successful fiber installation starts before the cable ever enters the conduit, pathway or cable tray. Installers should review the route, identify potential problem areas and confirm that the pathway is ready for cable installation.
Before pulling any fiber optic cable, check for:
- Sharp bends or tight turns
- Damaged conduit
- Obstructions or debris
- Overfilled pathways
- Improperly sized conduit
- Long pull distances
- Elevation changes
- Areas where the cable may be crushed, kinked or abraded
Whenever possible, use a pulling plan. For longer or more complex runs, calculate estimated pulling tension and compare that to the cable's recommended specification.
For example, Cleerline ruggedized cables (a common construction for long outdoor pulls through conduit and duct) support a pull rating up to 600 lbs, whereas standard indoor micro-distribution cables support a pull rating up to 225 lbs.
Always confirm the manufacturer’s published specifications prior to installation and do not assume one cable’s limits apply to another cable.
Never Pull Directly on the Fiber Strands
Fiber optic cable is designed with strength members that carry installation load. The glass fibers themselves should not be used as the pulling point. Nor should the cable jacket -- it can stretch, warp or tear when exposed to too much stress.
When pulling unterminated cable, attach a pulling grip or pulling-eye to the cable’s strength members (typically internal aramid yarn), not the optical fibers or outer jacket. Do this by removing a small portion of the cable's jacket with a cable stripper. Once exposed, the strength member can be looped inside a pull-eye, double-backed, then taped or knotted for security during the pull.
When pulling pre-terminated cable assemblies and patch cords, attach a pulling sleeve (also known as a pull-sock or pull-mesh) around the connectors and securely attach to the cable using the manufacturer's recommended guidelines. Never attach the pulling sleeve directly to the connectors, as they may disconnect during the pull.
Note that the pull strength of a pre-terminated cable is typically significantly less than an unterminated cable. Most pre-terminated cable has a 70 lb a pull rating or less.
Cleerline manufactures a variety of cable pulling kits that accommodate both unterminated and pre-terminated fiber optic cables. Heavy-duty solutions even support bulky armored and direct burial cables.
Respecting the pulling process is critical, as an improperly pulled cable can cause broken strands, increased attenuation, connector damage, microbends or macrobends, intermittent performance and ultimately failed certification testing. Even if a damaged cable appears intact on the outside, internal fiber stress can still degrade performance.
Respect the Cable's Bend Radius
Bend radius is another critical element during fiber installation. A cable that is bent too tightly can suffer signal loss, permanent fiber damage or long-term reliability issues.
There are usually two bend radius values: loaded bend radius and installed bend radius. Loaded bend radius is the minimum bend radius while the cable is under pulling tension, whereas installed bend radius is the minimum bend radius after the cable is installed and no longer under pulling tension.
The loaded bend radius is typically larger because the cable is under stress during installation. The Fiber Optic Association notes that a common recommendation is a minimum bend radius of 20 times the cable diameter while the cable is under tension during pulling.
When bend radius is a concern, installations typically turn to Cleerline's SSF and BendSafe fiber. Unlike traditional bend-insensitive optical cables, Cleerline SSF and BendSafe leverage patented constructions that greatly improve bend tolerances and, ultimately, cable durability. SSF in particular supports a minimum bend radius of 2.2mm compared to a typical bend-insensitive rating of 8.0mm.
Use Proper Lubricant When Pulling Through Conduit
Cable lubricant can reduce friction, lower pulling tension and help protect the jacket during conduit installations. However, not all lubricants are appropriate for all cable jackets. Use only lubricant that is compatible with the cable jacket material and the installation environment. Apply it evenly and follow both the cable and lubricant manufacturer’s recommendations.
Lubricant is especially useful for long conduit pulls, multiple bends, high conduit fill, underground duct installations and pulls with older or rough conduit.
Never use general-purpose oils, greases or chemicals unless they are specifically approved for cable installation.
Pull, Don’t Push — Unless the Cable Is Designed for It
Most fiber optic cable installations are designed around controlled pulling. Pushing fiber cable through a pathway can cause buckling, kinking or jacket damage, especially in longer runs.
Exceptions exist for certain air-blown fiber, microduct systems or specialty cable designs, but those systems have their own procedures and equipment requirements.
For standard conduit or pathway installations, use proper pulling equipment and controlled force. And if a cable does bind, stop immediately and never force the cable forward.
Finish the Installation
Once the cable has been successfully pulled, finish the installation by securing the cable run, installing a proper service loop and testing the cable's performance.
Fiber cable should not be stepped on, driven over, pinched under equipment or overly compressed with tight cable ties. Crushing can deform the cable structure and create microbends that increase signal loss. Only use cable mounting products that are designed for fiber optic installation and, when needed, choose a cable with a ruggedized or armored construction.
Service loops provide extra cable for future moves, adds, changes and repairs. However, service loops must be stored correctly. Always maintain the minimum bend radius and store the loop neatly. Avoid tight coils, but don't create excessive slack that can be snagged or damaged. Ideally, enclosures with loop trays should be used.
Finally, after the cable has been installed, test the fiber before turning the system over. Testing confirms that the cable was not damaged during installation and that the link meets performance requirements. Testing is not just a final checkbox -- it's the proof that the installation was completed correctly.
Final Thoughts
Fiber optic cable is designed for high performance, but performance depends on proper handling. The best installations are planned carefully, pulled under control and tested thoroughly after completion.
By respecting pulling tension, maintaining bend radius, protecting connectors and following the manufacturer’s specifications, installers can help ensure that fiber optic networks deliver the speed, reliability and longevity they were designed to provide.
Additional information on cable pulling kits and bend tolerant cable is available at Cleerline.com. A short video detailing cable pulling best practices is also available on the Cleerline website.