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High Fiber Cables—Are They for You?

In my magazine column back in July, I mentioned I had been trying to learn more about the new fiber optic cables with very large fiber counts. Today you can buy cables with 1,728, 3,456 and 6,912 fibers. What I wanted to know is why such cables exist, how they affect the role of the installer and how one decides if they make sense for an application.

Since then, I have gotten samples to analyze, heard from instructors and certified fiber optic technicians who have worked with them and visited a vendor myself to see how people work with these cables.

To begin, these cables are not for everyone. Today there are usually two types of users: owners of hyperscale data centers using them to connect facilities in a data center campus and telecommunication operators that install them in cities where they need large numbers of fibers for fiber-to-the-home or small cells for wireless networks.

Take a look at a couple of these cables.

Fiber optic cables cut open to reveal layers inside.
Examples of Corning’s RocketRibbon, which contain 3,456 fibers (top) and 1,728 fibers (bottom).

From this viewpoint they don’t look very different from regular cables but take a look at the same cables with a ruler at the ends for scale.

Two fiber optic cables cut in half next to a ruler. The smaller cable on the left contains less fiber than the larger cable on the right.

These cables are big. The 1,728-fiber cable is about 1-inch in diameter and the 3,456 is 1 1/4 inch (32 mm). They are also heavy. The smaller cable weighs 0.3-pounds-per-foot (0.45kg/m) and the larger cable is 0.5-pounds-per-foot (0.75kg/m). And they are very stiff. The minimum bend radius is 15 times the diameter, so a 1,728-fiber cable has a bend radius of 15 inches (375mm).

These cables are big, stiff and heavy because they are mostly fiber. Look at the photo above. A normal 144 fiber loose tube cable is about 15% fiber with the rest in plastic buffer tubes, strength members, plastic jacket and some filler for water blocking. These cables are about 50–60% fiber, and that extra density of glass is what makes them stiff and heavy.

All this adds up to a lot of issues for the fiber optic network owner, designer, contractor and installer to consider. But, is it a better choice if you need many fibers? Here are some issues I see.

Simply receiving a cable like this can be a problem. Is the loading dock capable of handling a 6–7-foot (1.8m) cable reel that weighs about a ton because that’s what a typical cable like this is delivered on?

A cable like this is not designed to be pulled like regular cable. It’s typically installed in conduit by blowing or jetting and using high-pressure air with special installation machines.

A contractor needs plenty of space for service loops because of the large bend radius, and some of the cables bend in only one direction because the strength members are in the jacket on opposite sides. Figure-eight movements for intermediate pulls on long cable runs require space and personnel because it will have large loops and is very heavy.

Splicing a cable like this requires a ribbon or mass fusion splicer. Most of these cables are based on ribbon fibers anyway, but if you tried to splice 1,728 individual fibers, it would take the better part of a month. Even with ribbons it may take close to a week. Here is a table that shows typical splicing times under best case conditions.

Splicing Ribbon Splicing Single Fiber Splicing
Fiber Count 1,728 1,728
Number of splices 144 (12 each ribbon) 1,728
Time per splice (approx.) 8 minutes 4 minutes
Cost per splice (approx.) $40 $25
Total time (approx.) 19 hours 115 hours
Total cost (approx.) $6,000 $43,000

Don’t even think about termination. You purchase prefab racks with enough terminations and splice the cable to the rack. These cables are not for everybody. For applications they were designed for, they are superb solutions. But think carefully before choosing one for your network.

About the Author

Jim Hayes

Fiber Optics Columnist and Contributing Editor

Jim Hayes is a VDV writer and trainer and the president of The Fiber Optic Association. Find him at www.JimHayes.com.

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