At a recent fiber optic technician training class, I heard some interesting stories about using existing pre-installed fiber optic links for various types of data communication.

The students for the class worked for a well-established Chicago-area installing and servicing contractor that focuses on fire alarm systems along with related technologies such as voice evac, building annunciation and other functions. This company was having difficulties with a particular installation where the fiber optic links for their equipment was connected.

There are literally millions of unused fiber optic links in the U.S. and Canada. The most common type of fiber cables that have been installed have either six, 12 or 24 fiber strands under one jacket.

Let’s use the six count as an example. If a client wanted to connect their 10/100/1000 Ethernet network from one telecommunications closet (TC) to another, they typically will only need two fibers to make the transmit/receive connections between the UTP to fiber interfaces. So, in this example, there might be six ports on the patch panel front, with two having jumpers connected and the other four covered with dust caps (hopefully).

So theoretically there are four fibers that could be used for additional connectivity. That thinking makes a very critical assumption that the existing fibers were properly installed, terminated with connectors and tested.

It is important for your companies’ sales engineers to understand that while using existing fiber links can greatly reduce installation costs — which should make the system more price attractive — it is quite possible that the fiber links in question may need to have new connectors installed; and it's possible that the cable was damaged during installation. Even if the client’s computer connection works that doesn’t mean the other fibers are any good.

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There’s been a lot of sloppy fiber optic work done in past years, and installation companies need to take caution when planning to use existing fiber links on a job. Here are a few of the installer errors I have personally seen:

Poor connector installation — Connectors have high loss, broken fiber faces or weren’t cleaned properly.

1. Slack cable management — At each end of a fiber link there should be between 20 and 30 feet of excess fiber cable at each end of the run. The excess should be properly mounted onto cable hooks and, after stripping off the outside jacket, the inner jacketed fibers should be coiled up inside the termination box. It is absolutely critical that proper fiber optic termination boxes be used; if the existing fiber links are not in a fiber-specific patch panel or box, that’s a dead giveaway of a poor installation.
2. Fiber links not terminated — In many cases a contractor taking a short cut will only terminate enough fibers for the client’s current usage requirements. If they want to connect a typical Ethernet network, they need two fiber links. Some contractors would only terminate two of the six fibers in a cable, leaving the other four loose and unusable until someone puts connectors or splices onto the spare fibers. In this example the client likely won’t check and won’t know that the other fiber links aren’t complete, as their computer network is working. Such negligent installation practices might not be discovered for years, until a company like yours asks to use the existing fibers for life safety or security connectivity.
3. Non-testing of installed fiber links — I have personally experienced this problem. A client had a six-count fiber cable pulled between their two telecom closets, and were using two to connect their network. I was working with a contractor friend and we were planning to use two of the existing fiber links to connect IP video cameras and a recorder. I was testing the existing fibers with an Optical Loss Test Set (OLTS), basically an 850 nm light source and meter. As most multimode fiber connections use 850 nm transmitters, testing the fibers at that wavelength tells the installer that the link is suitable. All of the six fibers tested very poorly, and because Mr. Murphy had been there first, the client had hooked up their computer network to the two worst fiber links that I had tested. I told the customer that all of the connectors should be replaced, but in the meantime, he could connect his network to the two “best” fibers, which tested as the best of the six. This greatly improved their network connection. And no, they didn’t call me back to replace their connectors at $100 each installed and tested good. Don’t look, maybe the problem will go away….

‘It is important … to understand that while using existing fiber links can greatly reduce installation costs — which should make the system more price attractive — it is quite possible that the fiber links in question may need to have new connectors installed.’

What needs to happen, before your company’s contract is signed where existing fiber links are to be used, is that a knowledgeable person come out to the client’s location to inspect and test the fibers that are planned to be used.

I think the first thing to do is to open up the fiber patch panel by pulling off the cover or opening the fiber connection box. Look at how the fibers have been terminated, and particularly how the cable and slack fiber have been stored. If you pull off the patch panel top and see a messy spaghetti of 900-micron jacketed fibers, you should be very suspicious of the fiber links’ quality.  Sloppy cable work indicates that sloppy connector installation is likely.

Here’s how it should look:

Orderly cable management within a fiber patch panel is some indication that the installer was competent. // IMAGE COURTESY OF DAVE ENGEBRETSON

While you’re staring at the patch panel, check the body style of the connectors on the backplane of the fiber connections. Today most patch panels will have “SC” style square connectors, but older panels may have the round “ST” type. Either one can work fine, as long as you plan to use the correct body style to match those in the patch panel.

If the patch panel cabling looks OK, the next step is to look at the outside jacket of the cable that in most all cases is stamped with the manufacturer, number and type of fibers (multimode or singlemode), NFPA fire rating for indoor cable, and a foot marker in either feet or meters.

If the cabling is multimode and was installed after 2005 it is likely to be labeled “50/125.” This is the current multimode fiber size in use; older multimode will be labeled “62.5/125.” Don’t be afraid to use older fiber cables IF they test good enough. Fiber is glass, doesn’t corrode, doesn’t rust, and unless the cable or connectors were damaged by accident or on purpose, older fiber strands will work just fine. Just be sure to use the correct internal sized fiber, i.e. use 50 micron connectors on 50 micron fiber, 62.5 on 62.5, etc.

If so far things are looking good, carefully remove one of the connectors on the backplane and put the face of the connector right on the lens of a bright flashlight. Another technician needs to be at the other end of the fiber links. Once the light is on the fiber, the light should be visible at the far end after the tech removes the dust caps.

You might have to move the fiber tip around on the flashlight lens to get the light to pass through.

The light test is the “no go” test. If a flashlight won’t pass from one end of a fiber link to the other, either one or both of the connectors are NG or the cable has been severed. If the light is visible, there is hope for that particular fiber link; it might test poorly but if it passes visible light the cable isn’t cut. One or both of the connectors will likely need to be replaced to achieve proper functionality.

All of this might sound complex, but it’s really easy if you know what to look for. Was the installation sloppy? Were all of the connectors installed in the patch panel? Does light pass through the link to the far end? Keep in mind that if a fiber is connected to port No. 4 on one patch panel, it may well be on another port in the far patch panel.

This is the important part. If your company plans to use any existing fiber links for an installation, the system contract must contain language something like: “ABC Installations plans to use existing fiber optic links as permitted by the system buyer for this system installation. ABC will test the fiber links and if they do not meet accepted industry standards there will be a time and materials extra cost for ABC to either repair or, if necessary, replace the fiber optic cables.”

This clause should be pointed out to the customer and they should be informed that there’s the possibility that the fibers may need some extra work to function properly.

Although my mother always wanted me to be a lawyer, please check with your own legal assistance to make sure your contracts and this clause are enforceable.

Fiber optics is great technology and can carry signals for thousands of feet or even 50 miles. Don’t be afraid of it; just be prepared to investigate existing fiber links that are to be used to verify their functionality. //