Top 10 Things You Should Never Do With Fiber Optic Cable

Written by Dave Harris, trueCABLE Technical Specialist, BICSI INSTC Certified

Fiber optic cable and copper twisted-pair cable share many similarities. They are both delivered in a coil or on a reel. They are installed in the same general location by the same people for the same general purpose. They even look similar, both before and after installation. But the physical difference in the copper and the glass conductors require different handling procedures. Imagine what happens when you twist a piece of wire, and compare that to what happens if you twist a piece of glass. It’s probably obvious that the glass fiber is more fragile, and should be treated with more care.

The transmission of data by light also presents other challenges, adding issues of safety and cleanliness. It might take some time and effort to get up-to-speed on fiber optic cable installation. We thought it might be useful to point out some things that many newcomers have to learn (or unlearn) on their way to fiber optic proficiency. You can learn more about installation of fiber optic cable in a related article, “How To: Install Fiber Optic Cable for Success.”

Feel free to check out the accompanied video below!

So, starting with some safety-related dont’s, here are the Top 10 Things You Should Never Do With Fiber Optic Cable.

1. Don’t look into the fiber end face.

The light produced by fiber optic lasers is invisible to the human eye. Nevertheless, it has enough energy to permanently damage a viewer’s retina. Even if the fiber appears dead, it might not be. It is crucial to form a conscious habit of absolutely never looking directly into that end face. It’s hard, but it’s okay. There’s really nothing there to see, anyway.

2. Don’t cut fiber optic cables without taking safety precautions.

Every time an optical fiber cable is cut in the field, small invisible glass shards can be produced. They are easily absorbed through the eyes, lungs and skin. Once this happens, our bodies have no way of removing them. This creates safety issues while processing fiber that are not present when working with cable made with metallic conductors. Always keep this in mind while working with optical fiber, and be prepared to work safely.

2a. Don’t mishandle fiber shards.

Although it is in everyone’s best interest to keep from producing fiber shards, sometimes it can’t be helped. While splicing optical fiber, the cleaving process produces unavoidable fiber waste. Anyone who cleaves fiber is also responsible for processing and accounting for this waste. So every cleaver should be accompanied by a sharps container for secure storage and identification of this potentially dangerous by-product.

Disposal container for sharps. (thorlabs.com)

2b. Don’t forget your PPE.

If your task will require you to cut fiber optic cable for any reason, you will need eye protection and airway protection. Even your skin is vulnerable to intrusion by tiny glass shards. Gloves should be worn while cutting, and during splicing procedures when feasible.

2c. Don’t expose others to unseen dangers.

You may have your PPE already in place, but others in the area might not. Be aware of the people around you while working with fiber optic cable. Make sure they are aware of any dangers they might be exposed to.

Consider a case where a company like yours has contracted to remove all of the equipment and cable from a data center so that the space can be upgraded or repurposed. It might be tempting to send in a crew of untrained laborers armed with Kevlar cutters to tear it all out as quickly as possible. But think about the environment that might be created for the unsuspecting demolition crew, and anyone else who needs to use the space in the future. In this scenario, people are depending on project managers and team leaders for their safety, and they probably don’t realize it without training. You can learn more about fiber optic safety in, “Comprehensive Guide to Fiber Optic Safety.”

2d. Don’t cut the fiber optic cable too short.

What’s the old adage? “Measure twice, cut once.” I know that cutting off too much cable isn’t actually a safety issue, but it is definitely something that should be avoided while cutting fiber cable. One will regret it if one does it, so this is a friendly reminder not to. And, it’s always good to end the safety briefing on a light note.

3. Don’t step on or otherwise crush your fiber optic cable.

Learning about how optical fiber works is one thing, but working with it is another. It might be necessary to examine old habits. We can toss a coil of copper cable in the truck bed without thinking, but we’d better think before we do that with a coil of optical fiber. To keep from crushing it, the trick is to protect your fiber from lateral (from the side) forces. So we try not to drop it, and we try to keep things off of it during storage and transportation. There are different constructions of fiber optic cable, and some can endure lateral forces better than others, but never assume that they can. The goal is to form some new cable-handling habits that minimize lateral forces and physically protect your fiber optic cable.

4. Don’t use pathways designed for copper cable.

Pathways for copper cable often make use of discontinuous supports that contact the cable every few feet or so. These supports, such as D-rings, bridle rings, and J-hooks work well for copper cable, but are not ideal for optical fiber. These supports end up causing the lateral force from the support to be localized, or concentrated in one spot on the cable. This can happen even if using ladder rack or basket tray. In most cases, the force is limited to the weight of the cable. But if the pathway is also occupied by other cables, especially heavy copper cables, the additional weight can cause signal loss in the fiber, and in extreme cases, the fiber can be crushed.

In the real world, we sometimes don’t get to engineer our own pathways and must use what’s already in place. If you are faced with this type of pathway, using flexible innerduct can provide a solution. The corrugated plastic tubing provides continuous support for the fiber, eliminating lateral force “hot spots.”

5. Don’t pull or bundle optical fiber with copper cable.

Pulling fiber optic cable along with copper cable is not recommended. The fiber can become braided among the copper cables, and that leads to lateral forces. Even if the fiber is being pulled alone, the natural tendency is for a cable to twist while it moves. Always attach your pulling apparatus using a swivel connector. This provides relief from torsional forces, so it keeps the cable from twisting, and helps to navigate conduit bends.

After installation, the fiber should still be kept separate from copper cable bundles. Flexible innerduct can help with this. It will not only keep them separate, but it also provides a ready pathway for installation of additional fiber cables.

A look above the ceiling in an old hospital building after decades of high-tech upgrades and retrofits. Optical fiber is protected within the orange corrugated flexible innerduct on the left.

6. Don’t pull bulk fiber optic cable by the armor or jacket.

The corrugated armor that is often found protecting a fiber optic cable looks like it is perfectly textured for a hand-hold. But don’t pull the fiber off the reel by grasping the armor. The armor covers the cable, but is not bonded to it in any way. It is possible to pull the armor right off the cable, especially if it is a long, heavy run.

The fiber cable should only be pulled by its strength member, which runs the length of the cable. The strength member is usually made of aramid (Kevlar) yarn, or sometimes metal. Its main characteristic is that it will not stretch or break, and pulling it will not damage the fiber. Pulling by the jacket or armor can pull the cable apart, and pulling by the optical fiber strands will destroy them.

In some cases, the aramid fibers are incorporated into the cable jacket. That allows the cable to be pulled by the jacket, because the jacket is the strength member. So, it can be important to know how your cable is constructed.

7. Don’t pull fiber optic cable too hard.

The maximum amount of pulling force that should be applied when pulling bulk fiber optic cable is 50 lbf. For pre-terminated fiber, the maximum tension for the pull sock is 16 lbf. Force exceeding this should be avoided as it may damage the cable jacket or break the glass fibers. If you feel a large amount of resistance or a “hard stop,” then stop pulling and investigate. Remember to make sure that you are pulling by the strength member.

8. Don’t bend it too tight.

Take care to keep from overbending or kinking the fiber optic cable. Every fiber cable we sell has its minimum bend radius listed in its specification sheet. Bending the cable too much will result in signal loss, as light passes through the tightly-bent jacket and escapes. Bending the fiber even further will cause the optical fiber to break.

Use sweeping bends when preparing conduit to avoid overbending the cable. Also, make sure fiber cables are adequately secured to avoid bending or kinking if disturbed while in service.

The development of “Bend-Insensitive Fiber” has led to cables that are less likely to break when bent, but even bend-insensitive fiber has a minimum bend radius that must be observed.

9. Don’t twist it.

Twisting optical fiber is another way to break it. As mentioned earlier, pulling cable without the use of a swivel attachment often leads to twisted cable. If that cable is composed of optical fiber, it is subject to damage by breakage, especially if the pull also involves copper cables.

There is another way to twist fiber cable that might not be obvious. If you have a coil of fiber, and you attempt to straighten it by pulling it apart like an accordion, you are twisting the fiber. Whether you are installing bulk fiber from a reel, or a fiber patch cord from a small coil, always make sure you straighten it by rolling it off the reel or coil.

10. Don’t remove the cap from your fiber end face without inspection and cleaning.

The #1 cause of fiber optic cabling failures is dirt on fiber end faces. I don’t know if there is some force (static charge, maybe?) that physically attracts dust particles to fiber end faces, but it sure seems like it. If you work with fiber optics, you are probably already in the habit of cleaning fiber end faces every time you remove the dust caps. If you are not already in the habit, you will be, if you want your fiber connections to function as expected.

Isn’t it possible that a speck of dust can land on the end face right after it’s cleaned but before it’s installed? Absolutely. It’s also possible to transfer a speck of dust from the cleaner itself. You can be reasonably sure of the condition of your end faces by including use of an inspection scope in your fiber cleaning procedure.

Fiber inspection scope

The inspection scope provides microscopic imaging of the fiber end face in real time. This can reduce the number of unnecessary cleanings and can help diagnose hard-to-find performance problems.

Conclusion

There are many, many things that you should never do with fiber optic cable, and it doesn’t take much imagination to conjure up a few more, some of which can be entertaining. But I really think that these are the top ten, with a few more thrown in for safety. Most of the installation requirements that are peculiar to fiber optic cable are actually included in these ten. After all, “Don’t use optical fiber to tow your truck” would just be an entertaining reminder to observe proper pull tension, and “Don’t tie it in a knot” is not an issue if you keep from exceeding bend radius limitations.

In general, what makes installation of fiber optic cable different to copper cable installation is the fragility of optical fiber. So the bottom line is, Be careful, and…

HAPPY NETWORKING!

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