FOA Guide to Fiber Optics 


Topic: Fiber Optic Installation  Table of Contents: The FOA Reference Guide To Fiber Optics

Fiber Optic Installation

All fiber optic applications are not the same. At the FOA, we're mainly concerned with communications fiber optics - telco, CATV, LAN, industrial, etc., but fiber optics are also used in medical or nondestructive testing inspection and lighting

Even within communications applications, we have applications that differ widely in usage and in methods of installation. We have "outside plant" fiber optics as used in telephone networks, CATV, metropolitan networks, utilities, etc. or "premises" fiber optics as found in buildings and campuses. We have fiber on "platforms" like cars, planes and ships (and the space station.)  Just like "wire" which can mean lots of different things - power, security, HVAC, CCTV, LAN or telephone - fiber optics is not all the same.

Since all these applications require different installation procedures, let's look at them in more detail.

Outside Plant (OSP)

plowing fiber

Direct Burying Cable By Plowing It In

Telephone companies and the Internet (which started on the telco backbone) all use lots of fiber optics, all of which is singlemode and most of which is outside buildings. It hangs from poles (aerial), is buried underground directly or pulled through conduit or is sometimes even submerged underwater. Most of it goes relatively long distances, from a few thousand feet to hundreds or thousands of miles (or kilometers) mainly in point-to-point links connecting phone switches.

FTTH
FTTH Optical Network Unit Electronics

One telco application is different, FTTH (fiber to the home.) Here the connection is from a phone switch in a central office or pedestal to the home. Most systems use passive optical network (PON) architectures with signals going through splitters that allow up to 32 users to share one link and carry bidirectional signals. These bidirectional signals, some carrying CATV too, require APC (angled PC) connectors. FTTH in new home construction is virtually all run underground in conduit while rebuilds in older neighborhoods may use aerial or underground construction. One new development is the usage of prefab cabling already terminated with weather-sealed connectors. 

aerial

CATV Amps and Splices On Aerial Cable

CATV systems also use lots of singlemode fiber in the backbone, using an overbuild architecture, bypassing coax already installed to connect local nodes that serve fewer subscribers with higher quality signals. The big advantage for CATV is reliability, as fiber is much more reliable than copper systems. Most CATV is aerial except in newer residential developments. Most CATV systems are analog optical conversions of coax signals, so reflectance of connectors is a big  problem, requiring APC (angled PC) connectors.

opgw 

Coils of OPGW On A High Voltage Tower Spliced To Underground Fiber Optic Cable

Utilities also use lots of fiber. Many new high voltage distribution lines have optical fibers in the center of the ground wire (OPGW - optical power ground wire) that are used for grid management and communications, sometimes even leasing lines to telcos for long distance signals. Utilities also use fiber in substations for control signals, since fiber is not affected by high voltages or electrical noise. Unlike the long distance links, these fiber links generally use multimode fiber, sometimes even step-index PCS fibers for their low speed signals.

traffic signals  
Traffic Control Cable Spliced In Pedestal

Municipalities are becoming big users of optical fiber too. Rather than use lots of telco phone lines for data, it's usually cheaper to install their own town-wide network. Adding traffic controls and CCTV surveillance cameras is also common. Some cities have gone ahead and offered connections on their own data network to businesses and homes when telcos or CATV companies are not offering broadband services at adequate speeds. Again, most of these networks are singlemode fiber, often underground in existing conduits but sometimes on utility poles.


Outside Plant Installation

Most outside plant installations are singlemode fiber, and telco cables often have very high fiber counts, up to 288 fibers or more, with a growing percentage being ribbon cables. CATV or utilities use more loose tube cables with lower fiber counts. Cable designs are optimized for the application: cables in conduit for pulling tension and resisting moisture, buried cables for resisting moisture and rodent damage, aerial for continuous tension and extreme weather and undersea for resisting moisture penetration. Installation may require special equipment like pullers or plows, and even trailers to carry giant spools of cable. Undersea applications require special cable-laying ships.

OSP cables are generally loose tube, ribbon or slotted core design. Jackets are chosen to withstand an outdoor environment appropriate for the application, usually black polyethelyne (PE.).  Strength members must be strong enough to absorb all the tension loads in the installation process or long term loads from aerial installation. Cables usually include fiberglass rod stiffeners in the center to prevent kinking. Jackets may be doubled with armor between them to prevent rodent penetration or crushing or strength member to allow pulling by the jacket. More on cables:  1,  2

Cables should be pulled with swivel pulling eyes to prevent causing a twist in the cable. OSP installations in conduit may require lubrication to reduce frictional loads and/or intermediate pulls. Intermediate pulls require pulling the cable to a point, laying onthe ground in a "figure 8" pattern to prevent putting a twist in the cable, then pulling the next section. Care should be taken to not pull cable around courners too tightly, with a minimum bend radius of 20 times the cable diameter under tension, although cable can have a bend radius of 10 times the cabel diameter under no tension.

Long distances mean cables are spliced together for higher reliability and lower loss, since cables are not manufactured longer than about 4-12 km (2.5-7 miles) depending on cable type, and most splices are by fusion splicing. Splices are placed in sealed splice closures designed for the particular application (buried, pedestal, aerial, etc.) Singlemode cable is generally not field terminated, since polishing for low loss and reflectance requires much care and is hard to do by hand. Connectors (generally SC or LC styles) on factory made pigtails are usually fusion spliced onto the end of the cable.

After installation, every fiber and every splice are generally tested with an OTDR and data stored for future reference in case of damage requiring restoration.
For outside plant networks, the installer usually has a temperature controlled van or trailer for splicing and/or a bucket truck for aerial work. Installation equipment may include fusion splicers, OLTSs, OTDRs and other special cable handling equipment which can be quite expensive.

Many outside plant telephone installs for the big telcos are done by the telco themselves, while a small number of large, specialized installers do installs for independent telcos, CATV companies, utilities and municipalities.



Premises Cabling

By contrast, premises cabling- cabling installed in a building or on a campus - involves shorter lengths, rarely longer than a few hundred feet, with fewer fibers per cable typically. The fiber is mostly multimode, except for the forward-thinking user who installs hybrid cable with both multimode and singlemode fibers for future high bandwidth applications. Premises cabling standards, also called structured cabling standards, are covered in the TIA-568 standard for commercial building cabling, installed in a "star architecture" Fiber has become so popular for premises applications that the appropriate industry standard, TIA-568, allows fiber in the backbone, to the desktop, in zone cabling and centralized fiber cabling.  Centralized fiber cabling uses no copper cables at all and allows siting all the electronics in the main computer room and at the user, not requiring hubs or switches in telecom closets. Centralized fiber cabling therefore needs no power, grounding or AC in telecom rooms, nor in fact, even a telecom room itself, and thereby offers considerable potential for cost savings if properly designed.

LAN

Typical LAN Fiber Equipment

LANs - local area computer networks - are one of the most common premises applications for fiber. Since fiber was first used for LANs, speeds have increased from 10 Mb/s (millions of bits per second) to  10 Gb/s (billions of bits per second) with 40 or even 100 Gb/s on the horizon. During that time, most fiber installations used 62.5/125 (OM1) or FDDI-grade fiber (FDDI was the first 100 Mb/s network based solely on fiber) while copper went through 2 grades of coax cable, shielded twisted pair and Categories 3, 4, 5, 5E, 6 and 6A unshielded twisted pair copper (UTP.)

LANs today combine fiber backbones, Cat 5e or Cat 6 to desktop computer users and fiber or copper to wireless access points, generally  following the TIA-568 standard's guidelines. With more users choosing wireless for mobility, not only for laptops but for mobile wireless devices like smart cell phones, desktop wiring is becoming less common and multiple wireless access points more widely deployed. Many telecom rooms (which used to be called telecom "closets" before they became filled with LAN electronics, still contain large amounts of copper (blue in the photo below) and fiber (orange.) A new type of optical LAN based on fiber to the home (FTTH) passive optical LAN technology is becoming popular too. More on OLANs.

telecom closet

Telecom room with copper and fiber connecting network electronics

Since the advent of Gigabit Ethernet which uses VCSEL lasers for their high modulation speed, an old fiber design from 1980, 50/125 fiber (OM2), which is more compatible with lasers than 62.5/125, has become the fiber of choice for most LAN installations. Manufacturers have further developed 50/125 fiber into "laser optimized" fiber (OM3) that has higher bandwidth capability and is the ideal choice for current installations. Manufacturers are working on even higher performance 50/125 fiber (perhaps to be called OM4) for 40 or even 100 Gb/s networks. Still, many users install hybrid cables with both OM3 and singlemode fibers in backbones since SM fiber is cheap and provides virtually infinite bandwidth for currently unknown future uses.


cable trays

Fiber and Copper Cables in Cable Trays

Premises cables can be installed in cable trays, conduit, innerduct or special types of cable hooks. Installation of the cable must be carefully done to prevent snagging and kinking the cable as it is pulled among the numerous hazards in a typical building installation. Fiber optic cables should not be mixed with copper cables as the heavier copper cables can stress the fiber cables. Sometimes the fiber is hung below cable trays to protect it from masses of copper. Vertical cable runs are common in buildings. Vertical cables are preferably installed by dropping the cable down rather than pulling them up, using proper hangers and service loops to prevent stressing cables.

SANs or storage area networks in data centers are another popular fiber application. At 10 Gb/s, UTP transceivers consume vast amounts of power, 4-10 times more than fiber transceivers, so most data centers use coax for short links and fiber for over 10 meters. Data centers often run cables under the floor. Most false floor systems include cable trays for fiber optic cables.  An armored indoor cables is sometimes used in underfloor applications to protect the fiber from crushing by other cables.

underfloor Underfloor fiber optic cable in tray

 CCTV Cameras

Security systems use lots of fiber. Airports and many public buildings have CCTV cameras located too remotely for coax connections without repeaters, so media converters or fiber-compatible cameras are used. Where security is important, like airports, cables are usually run in metal conduit where fiber's small size is a big advantage. Fiber bandwidth allows multiplexing many cameras onto one fiber too. Most security systems offer fiber options or can be easily converted with a commercial media converter. Fiber can even be used for a perimeter intrusion sensor.

cctv

CCTV camera in Boston "Big Dig" tunnel

aerial cctv camera

Aerial CCTV camera installation

Industrial applications of fiber are widespread. Fiber's distance and bandwidth capability is less an issue here, but immunity to noise and ruggedness is very important. Data gathering and machine control (especially robots) are big applications. Power controls are another important application. For protection, cables are often run in metal conduit where fiber's small size is another big advantage.

Premises Installation

Common to all premises applications is short links compared to OSP. LANs typically have links shorter than 300m. Industrial systems are similarly sized. Even security cameras run only 1-2Km typically, except some links at major airports.

Splicing is practically unknown in premises applications. Building cables are generally installed in one piece. Cables between buildings can be bought with double jackets, PE for outside plant protection over PVC for building applications requiring flame retardant cable jackets, so cables can be run continuously between buildings. Today's connectors often have lower loss than splices, and patch panels give more flexibility for moves, adds and changes.

Premises fiber optic cable is usually tight buffer cable. Simplex or zipcord cable is used for some applications where only one or two fibers are needed. Backbone cables, which may contain 24-96 fibers, are usually distribution style cables. Smaller fiber counts and harsh (e.g. industrial) environments often require more rugged cables like breakout designs. All cables installed indoors must be rated for flammability per the NEC, CEC or similar safety organizations worldwide.  More on cables:  1,  2.   

Most connectors are SC or ST style with LCs becoming more popular since most transceivers of Gb/s speeds and above use LCs. Termination is usually by installing connectors directly on the ends of the fibers, primarily using adhesive or prepolished splice techniques. Testing is done by a source and meter, but every installer should have a flashlight type fiber tracer to check fiber continuity and connection.

Unlike the outside plant technician, the premises cabler (who is often also installing the power cable and Cat 5/5e/6/6A for LANs too!) only needs a termination kit and OLTS or source and power meter test kit. The premises installer probably has an investment of less than $2,000 in tools and test equipment.



The Installers

There are thousands of cabling installers who do fiber optic work. They've found out it isn't "rocket science," and their initial investment in training, tools and test equipment is rapidly paid back. Few installers do both outside plant and premises cabling because of the difference in the applications. The companies that do both are usually very large and often have separate divisions doing each with different personnel. Most contractors do nothing but premises cabling.


Fiber Optic Cable Plant Installation

Fiber optic cable may be installed indoors or outdoors using several different installation processes.  Outdoor cable may be direct buried, pulled or blown into conduit or innerduct, or installed aerially between poles. Indoor cables can be installed in raceways, cable trays above ceilings or under floors, placed in hangers, pulled into conduit or innerduct or blown though special ducts with compressed gas. The actual installation process will depend on the nature of the installation and the type of cable being used.

Since there are so many types of fiber optic cable and so many different applications, it is hard to cover each application in detail. However there are some general rules that should be followed:

Safety

Safety on the job site must be the number one concern of everyone - installers, supervisors, owners, etc. Besides the usual safety issues for construction, generally covered under OSHA rules, fiber optics adds concerns for eye safety, chemicals, sparks from fusion splicing, disposal of fiber shards and more. Before beginning any installation, safety rules should be posted on the job site and reviewed with all onsite personnel. Chemical MSDS (material safety data sheets) for any hazardous substances should be available from the supervisor. All personnel must wear the usual construction safety gear plus everyone must wear eye protection whenever working with fiber. Here are safety rules for fiber optics.

Training

All personnel involved in any fiber optic installation must be properly trained and familiar with the tools, components and processes to be use during the installation. Training must also include all safety procedures. An installer should never use the job site to learn new products or techniques. Test equipment should be checked for proper operation, including condition of reference cables, charge level of batteries and tested to ensure proper measurements can be made. Personnel should have proof of basic knowledge, skills and abilities (KSAs) such as the FOA CFOT certification.


Pre-Installation

No installation should begin until there is a complete design, all equipment and components have been chosen, the cable routing is determined and any permits or coordination with other groups is ready. Cable documentation should be started before installation so the installation is properly documented and ready for labelling and recording test data. Documentation will facilitate installation, allow planning for upgrades and provide data needed for restoration.
Components must be ordered and delivered to the job site before installation can begin. Relevant personnel who will be affected by the install, for example those located in the installation area or who may lose communications services, must be notified. If the installation takes more than one day, arrange security to guard the equipment and components left on the construction site.


More on fiber optic network design.

REMEMBER: Safety rules should be posted on the job site(s) and reviewed with all supervisors, installation personnel and any affected parties. Download a FOA safety poster.

During The Installation

Inspect all installation workmanship during the installation itself so any problems can be identified and solved before they become major issues. Daily supervisors and installers should review processes, progress on the job and test data. All affected personnel should receive immediate notification of problems and solutions, shortages, etc.
Be careful when installating cables to avoid stress, hazards that may snag cables and kink them or installing cables where heavier cables may be placed on top of them.
Bundling cables for neatness is fine, but be careful using cable ties. Tightening them can put harmful stress on the fibers (or pairs in UTP copper cables), so hand tighten them and cut off the excess length. Even better, use soft "hook and loop" ties that can be reopened to move cables.

Safety and Building Codes

All installations must follow building and fire codes for safety. All components must be appropriately rated for the application (premsies or OSP) and properly installed. Indoor applications require rated fire-retardant components and firestopping at walls or floor penetrations. All metal components of a cabling system must be properly grounded and bonded. Documentation should include all issues required by building codes.
The National Electrical code now requries removal of all "abandoned" cabling as a fire hazard. This should be considered as part of the planning of an installation as cable removal should be done first if possible to avoid interference with newer cables.

After completion of cable plant installation

Inspect the workmanship of all parts of the installation. This includes visual inspection of the work site for neat installation workmanship and reviewing test data on cable plant. Appropriate personnel should set up and test the communications system that will operate over the fiber optic cable plant to ensure it is proper for that system.
Before the job is completed, it is important to update and complete documentation and the restoration plan. Cable and component remainders should be stored along with the restoration plan and documentation in case of future network outages requiring cable plant restoration.

Additional reading on specific areas of cabling installation: Premises Cabling Installation, Outside Plant (OSP) Cabling Installation  

Read more on installation.

Download a free copy of the NECA/FOA-301 Fiber Optic Installation Standard.


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Table of Contents: The FOA Reference Guide To Fiber Optics



 


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