From Fluke Networks, the fiber optic test equipment company

Guide to Fiber Optics


Fiber Optic Cable

The job of the cable is to protect the fiber. Fiber comes in lots of different types, depending on the number of fibers and the places it will be installed in. Choose fiber carefully, as the choice will affect how easy it is to install, splice or terminate and, most important, what it costs!
Choosing a cable
If you have to make the choice of cable to use instead of it being specified by your customer), you will be dazzled by the choices. Since the cable's job is to protect the fibers from the hazards encountered in an installation, there are so many types to choose from. It all depends on where the cable will be run. Inside buildings, cables don't have to be so strong to protect the fibers, but they have to meet all fire code provisions. Outside the building, it depends on whether the cable is buried directly, put in conduit, strung aerially or whatever.
Your best bet is to contact a few cable manufacturers (two minimum, three preferred) and give them the specs. They will want to know where the cable is going, how many fibers you need and what kind (singlemode or multimode or both in what we call hybrid cables.) Some cables have metal strength members or even metal signal or power cables, and we call them composite cables. The cable companies will evaluate your requirements and make suggestions. Then you can get competitive bids.
Since the plan will call for a certain number of fibers, consider adding spare fibers to the cable. That way, you won't be in trouble if you break a fiber or two when splicing, breaking out or terminating fibers. And request the end user consider future expansion. Most users install lots more fibers than needed, especially adding singlemode fiber to multimode fiber cables for campus or backbone applications.
Cable Types
All cables share some common characteristics. They all include various plastic coatings to protect the fiber, from the buffer coating on the fiber itself to the outside jacket. All include some strength members, usually a high strength "aramid" yarn often called "Kevlar" which is the duPont trade name, to pull the cable with without harming the fibers. Bigger cables with more fibers usually have a fiberglass rod down the middle for more strength and to limit the bend radius. Here is a quick rundown on the standard cable types so you will know what the cable maker is talking about:
Simplex and zip cord: One and two fibers, tight-buffered, with Kevlar strength member and jacketed. The jacket is usually 3mm (1/8 in.) diameter. Zipcord is simply two of these joined with a thin web. It's used mostly for patch cord and backplane applications, but zipcord can also be used for desktop connections.
 
Distribution cables: They contain several double-buffered fibers bundled under the same jacket with Kevlar or fiberglass rod reinforcement. These cables are small in size, and used for short, dry conduit runs, riser and plenum applications. The fibers are double buffered and can be directly terminated, but because their fibers are not individually reinforced, these cables need to be broken out with a "breakout box" or terminated inside a patch panel or junction box.

Breakout cables: They are made of several simplex cables bundled together. This is a strong, rugged design, but is larger and more expensive than the tightpack or distribution cables. It is suitable for conduit runs, riser and plenum applications. Because each fiber is individually reinforced, this design allows for quick termination to connectors. Breakout cable can be more economic where fiber count isn't too large and distances too long, because it requires so much less labor to terminate.

Loose tube cables: These cables are composed of several fibers together inside a small plastic tube, which are in turn wound around a central strength member and jacketed, providing a small, high fiber count cable. This type of cable is ideal for outside plant trunking applications, as it can be made with the loose tubes filled with gel to prevent harm to the fibers from water. It can be used in conduits, strung overhead or buried directly into the ground. Since the fibers have only a thin buffer coating, they must be carefully handled and protected to prevent damage.
Even More: There are other cable types like ribbon cable (and some different names for the ones shown above). Every manufacturer has it's own favorites, so it's a good idea to get literature from as many cable makers as possible. And check out the little guys; often they can save you a bundle by making a special cable just for you!
Cable Ratings and Markings
All cables must carry identification and ratings per the NEC (National Electrical Code) paragraph 770. Cables without markings should never be installed as they will not pass inspections! These ratings are:
OFN optical fiber non-conductive
OFC optical fiber conductive
OFNG or OFCG general purpose
OFNR or OFCR riser rated cable for vertical runs
OFNP or OFCP plenum rated cables for installation in air-handling plenums
OFN-LS low smoke density
Pulling Fiber Optic Cable
Pulling fiber optic cable isn't hard at all, since the manufacturer takes great pains to make sure the cable design protects the fibers during installation. Fiber cable can be pulled with much greater force than copper wire if you pull it correctly. Just remember these rules:
Do not pull on the fibers, pull on the strength members only! The cable manufacturer gives you the perfect solution to pulling the cables, they install special strength members, usually duPont Kevlar aramid yarn or a fiberglass rod to pull on. Use it! Any other method may put stress on the fibers and harm them. Most cables cannot be pulled by the jacket. Do not pull on the jacket unless it is specifically approved by the cable manufacturer and you use an approved cable grip.
Do not exceed the maximum pulling load rating. On long runs, use proper lubricants and make sure they are compatible with the cable jacket. On really long runs, pull from the middle out to both ends. If possible, use an automated puller with tension control, but we've seen jobs done with a mule providing the pulling force!
Do not exceed the cable bend radius. Fiber is stronger than steel when you pull it straight, but it breaks easily when bent too tightly. If you put a kink in the cable, you will harm the fibers, maybe immediately, maybe not for a few years, but you will harm them and the cable must be removed and thrown away!
Do not twist the cable. Putting a twist in the cable can stress the fibers too. Always roll the cable off the spool instead of spinning it off the spool end. This will put a twist in the cable for every turn on the spool! If you are laying cable out for a long pull, use a "figure 8" on the ground to prevent twisting (the figure 8 puts a half twist in on one side of the 8 and takes it out on the other, preventing twists.) And always use a swivel pulling eye, because pulling tension will cause twisting forces on the cable.

Make sure the cable is long enough for the run. It's not easy or cheap to splice fiber and it needs special protection. Try to make it in one pull, possible up to about 2-3 miles.
Conduit and Innerduct: Outside plant cables are either installed in conduit or direct buried, depending on the cable type. Building cables can be installed directly, but you might consider putting them inside plenum rated innerduct. This innerduct is bright orange and will provide a good way to identify fiber optic cable and protect it from damage, generally a result of someone cutting by mistake! The innerduct can speed installation and maybe even cut costs. It can be installed quickly by unskilled labor, the fiber cable pulled through in seconds. You can even get the innerduct with pulling tape already installed.
Cable Plant Hardware: This is much too much of a discussion to include here. There are tons of types of hardware and tons of manufacturers who make it. Gather up catalogs from the hardware makers and/or distributors to see the variety. Look at the places where you will put it and pick termination boxes or patch panels appropriate for the location. If you can, choose panels that have the connections behind locked doors, since the biggest problem we see is connectors broken at the back end by people messing around in communications closets! Fiber doesn't need maintenance or inspection. Lock it up and only unlock it when you have to move something!
Designing Networks
I guess this is too big a topic for a comic book! But we'll pass along some hints to make life easier. First and foremost, visit the work site and check it out thoroughly. Know the "standards" but use common sense in designing the installation. Don't cut corners which may affect performance or reliability. Consider what are the possible problems and work around or prevent them. There ain't no substitute for common sense here!
Fiber's extra distance capability makes it possible to do things not possible with copper wire. For example, you can install all the electronics for a network in one communications closet for a building and run straight to the desktop with fiber. With copper, you can only go about 90 meters (less than 300 feet), so you need to keep the electronics close to the desk. With fiber, you only need passive patch panels locally to allow for moves. Upgrades are easy, since the fiber is only loafing at today's network speed!
 
A big item is install spare fibers. If you are trying to get 48 fibers and you break one near the cable, you're out of luck if you don't have a spare. Fiber is cheap! Add a few extra fibers in as insurance, and maybe convince the user to add some singlemode fibers to a multimode fiber for future high speed networks.
Estimating and Bidding
These are two different topics. Estimating is necessary to figure out what the job will cost you. The goal of bidding is getting the job at a price that will allow you to make a profit. BIG DIFFERENCE! We can't teach you either here. We suggest you read Chapter 12 & 14 in The Fiber Optic Technicians Manual carefully and try to understand what it really costs you to do any task you must bid. Whatever, never bid blind - make a site visit.
Remember setup time! A manufacturer say you can terminate his connector in 3 minutes, and you can do it yourself in the office. But how long does it take to get the equipment to the site, set up, and do the terminations, clean up, pack and go home? Add that to the termination time to get a realistic time.
And finally, consider yield. You will never get every connector or splice right the first time. If you get 90% good in the field, you are a hero! Consider that, plus lost cable lengths, etc. when you bid.
If you bid accurately, you will never regret losing a job to a lower bidder, 'cause you know that the winning bid is close to or losing money, and that is not the goal of running a business. Bid accurately and you will stay in business!
Responding to RFQs
Before you quote a job, make sure you really know where the cables will be installed. Look for difficult places you must work. You must know what types of cable, connectors, splices, hardware, etc. the customer wants (including brands - if specified). Put it all together, then get a co-worker to evaluate where you missed something. Don't be afraid to talk to the customer and suggest things that will save him (and you) money.
If you see a specification that doesn't make sense (like the all-too-common one of asking for OTDR test data on short LAN cable runs), tell the customer before you bid. Don't bid blindly. If you need equipment or training for the job, make darned well sure you know what it really costs.
We said it before and we'll say it again: make a site visit yourself and look for problem places. Trust us, we have seen every mistake made we mention and more! You want to get a top quality working installation at the best price, so you have to remember all the gruesome details. Double- then triple-check everything. You won't regret it!
Documentation
Knowing where every cable, connector, splice, patch panel, etc. goes and the length of every cable is more than helpful. It can help you in bidding, buying, installation, testing and restoration. After installation, keep test data to refer back to when you have problems. Users understand the value of documentation and understand it can lead to higher bids, but good documentation pays for itself.
Don't Get In Over Your Head! Never try to do an installation when you are not fully familiar with the particulars of the installation: location, components, procedures, etc. We know contractors who have lost hundreds of thousands of dollars because they took jobs without proper training or experience. If you want to take a job in a new arena, find an expert in that specialty and hire them to help at least in the beginning. Mistakes are very expensive in this business...