PLANNING THE INSTALLATION

Transcription

1 C H A P T E R 12 PLANNING THE INSTALLATION THOMAS A. DOOLEY AND JERALD R. ROUNDS THE PROCESS OF PLANNING Planning is one of the most important parts of any project and is particularly critical in construction. One of the characteristics of construction is that it is not repetitive. Although specific activities such as pulling cable or making terminations appear to be repetitive, each is done under different circumstances. The cumulative result of these small differences is that jobs differ considerably. As a result, each job must be planned in detail to take its unique characteristics into consideration. In manufacturing, prototypes are designed and manufactured to test the design and the manufacturing procedures. When mistakes and oversights occur, another prototype is developed to solve the problems. This process is repeated many times over until both the product and the process of making that product are flawless, at which time the product goes into production. In the construction industry, you do not have that luxury. Designers must design correctly the first time. Constructors must build right the first time. Errors, either in design or construction, are costly to repair or replace and cause time delays. Some errors are hidden and do not become obvious until the system is operating. Then, the mistakes become not only costly and time-consuming, but 129

2 130 CHAPTER 12 PLANNING THE INSTALLATION are disastrous to those who depend on a fully operational and properly working system. The only way to produce a quality job is to avoid errors, omissions, and mistakes by properly planning and by establishing correct installation procedures. A side benefit of the planning process, of course, is that it improves the efficiency of installation, which results in higher profits for a contractor. Preplanning of every aspect of fiber optic installation is not an option; it is a necessity. MEASURING FOR CONDUIT PULLS Planning for proper cable lengths is extremely important in fiber optic installation for two reasons. The most important is that splices cause loss in both signal quality and strength this should be avoided. In fact, most designers specify point-to-point or device-to-device runs to avoid needless signal loss due to splices. The second reason, especially important to the contractor, is that splices cost time and money. Measurements must be taken by an experienced field hand who understands the importance of correct and accurate measurements. Often, this is done by the project engineer or the job site superintendent. There are three ways to measure the path to be used for the fiber. They are listed from least to most desirable. 1. Measurements taken from the set of prints. This works if you want to invest in a great deal of extra material. The objective of design drawings is to show generally where runs are supposed to be located. However, it is virtually impossible for the designer to anticipate all field conditions, and it is not the designer s intent to do so. Thus, taking accurate measurements from the design drawings is not possible and results in runs that are, at best, marginally long or short. Long pieces of fiber must be recut and short pieces are wasted. 2. Field measurements taken with a wheel. A site visit with a measuring wheel and a set of drawings will yield much better accuracy. Certain characteristics of the job site are given perspective with a field visit that are not obvious from inspection of the drawings alone. During the site visit, the drawings can be verified for accuracy, installation details such as pulling locations can be noted, changes such as variations in alignment or elevation can be identified, obstacles that might hinder the pull can be discovered, and termination locations can be recorded. 3. Measuring with measurement/pull tape. By far the most accurate and efficient method of measurement is with measurement/pull tape (sometimes called mule tape). This is a flat ribbon, consecutively numbered in feet, that is usually made with polyester or aramid yarn and sometimes

3 CHAPTER 12 PLANNING THE INSTALLATION 131 coated with plastic for waterproofing. It comes in different lengths and pull strengths. Completing the measurement process requires adding extra length for splices, terminations, and future access coils, if specified. The amount of additional cable needed for splicing depends on site conditions, splicing method used, and long range plans for cable usage. Termination needs only about 7 to 10 feet of additional cable beyond the place the terminal will be mounted. Access or repair coils generally range in length from 30 to 50 feet per span. A good guideline is to allow 1 percent extra for outside plant cable and 5 to 7 percent extra for inside cable. SPLICING Fusion splicing cannot be done in explosive environments such as manholes. Therefore, each end coming into the splice that will finally end up in the manhole will have to have enough length to reach a tent or van near the manhole where the splice will actually be made. Usually, about 30 feet of extra length should be added for each side of the splice resulting in additional 60 feet of cable. Mechanical splicing can be done inside manholes. Mechanical splices require only about 10 feet of overlap, instead of the 60 feet for a fusion splice. Remember that these measurements are in addition to whatever length will be required to properly rack the cable within the manhole. TERMINATIONS When terminating fiber, it is important to place the terminal in a safe, noncongested area. If the end user has no preferences, place the terminal as close as possible to the fiber optic transmission equipment. It is most important to protect the exposed fibers, so choice of a termination location must consider a working environment that allows adequate working space. EFFICIENT PULLING When installers first become involved in fiber optic installations, they can easily become overconfident about how much cable length can be successfully pulled at one time. This is probably because of the small size and weight of fiber optic cable. It is better to divide a pull in half, or even thirds, usually at corners or pull boxes, than to fail in pulling a long run. A pulling operation must be discontinued when the pulling tension reaches the cable limit. The discontinued pull will have to be aborted, the cable pulled back out and replaced on the reel, and the pull started again, either with shorter

4 132 CHAPTER 12 PLANNING THE INSTALLATION runs or better lubrication or both. The cable may be reused if the pull or extraction has not damaged it. Every effort must be made to plan the pull so that pulling locations have plenty of work space. The knowledgeable designer will designate several appropriate locations for breaking up the pull. The installer must ensure that if the designer has not indicated where multiple pulls are necessary, he or she can determine appropriate locations for intermediate pulls before work is begun in the field. It is better to tie up one lead technician before the pulling starts than the whole crew after it has begun. Most point-to-point pulls can be accomplished by crews of two or three people. One person pays the cable off the reel and into the duct in order to reduce tail load (the term used to designate that force required to get cable off the reel and into the duct). One or two people pull at the other end. The size of crew is determined by considerations such as: Length of pull Total degrees of bend Tail loading Use of lubricant Use of power pulling equipment When planning to start a pull, the installer must make sure there is enough time to finish the job the same day. It is unwise to leave half a reel of cable, worth anywhere from $5,000 to $375,000, lying around in unsecured areas. If a reel must be left exposed to the public, strong consideration should be given to assigning a security guard to watch over the reel. An occasional investment of $75 or $100 to avoid theft of an expensive reel of cable, to say nothing of the disturbance to the job if the cable is gone when installers arrive to begin work in the morning, is a wise investment Exact terminating locations must be identified in advance. This obvious though often overlooked step can lead to costly mistakes if forgotten. The cable must be pulled all the way to where it will be terminated, not just into the room. The designer should provide a fold-flat diagram (which results from folding out the walls of the room as if they were the sides of a box hinged at the intersections of the walls and the floor) for each terminating room as a part of the initial planning walkout. ADEQUATE DUCT SPACE Current industry practice, outside telephony, tends not to utilize available duct space very efficiently. As a result, one often finds a 1/2-inch fiber cable as the only cable in a 4-inch duct. As a matter of good design, cable should fill approximately 60 to 70 percent of the available duct space.

5 CHAPTER 12 PLANNING THE INSTALLATION 133 Since it is difficult to pull cable into a duct that is already occupied, it is very important to detail, on the print, where the different media will be pulled. Since most fiber cables are 3/4-inch or smaller in diameter, for efficient use, the larger 3- or 4-inch diameter conduits should be subdivided with innerducts. Innerduct is flexible, nonmetallic conduit that is pulled in multiples into the main conduit. It is made of polyethylene and comes with a pull rope already installed within it. Innerduct serves a threefold purpose: Subdividing the main duct Protecting the fiber cable Reducing friction The inside of the innerduct is designed to let the cable glide smoothly within it. This is accomplished by the use of special coatings and by the physical properties of the inner wall. Corrugated innerduct is the most popular form because of its flexibility. A 3-inch conduit can be subdivided with up to four 1-inch innerducts; up to six 1-inch innerducts can be placed in a 4-inch conduit. Innerduct not only allows the initial fiber installation to be effectively accomplished, but allows expansion capabilities to be built into the system. This can provide great return on investment if there is any expectation of future expansion of the fiber system. INITIAL PLANNING WALKOUT Prior to the start of cable pulling, a planning walkout should be performed by the project engineer, the lead technician, and the project superintendent. The project engineer, responsible for system design, will be well aware of the customer s needs. The lead technician, an experienced fiber installer who will not necessarily be the one who will do the installation, has the responsibility to plan and to answer as many questions as possible before the crew is on site. The superintendent can provide general project information and needs to know as much as possible about the installer s activities to coordinate with other trades and activities in the vicinity of the installation. The walkout should start at one termination site (Figure 12-1). This location will be designated with a clearly stated name, such as #12 Communication Room. A rough fold-flat sketch will identify the fiber terminal location and locations of other major system components, as well as other relevant features in the room. The floor and walls will be marked with a pencil to indicate approximate locations of terminations. Notes should be made on the sketch concerning conduit type and size, as well as whether pull string or measurement/pull tape has been used. Verification of whether multiple ducts are involved is requested from the superintendent.

6 134 CHAPTER 12 PLANNING THE INSTALLATION Room Location for Terminations 2 Bends 3 Conduit Size 4 Manholes 5 Pull Locations Figure 12-1 Preplanning walkout sketch. Identification should be made defining which conduits go where either by visual inspection or by tugging on the pull tape. The path of the conduit should then be walked, making note on the diagram of any pull boxes, manholes, or other abnormalities. This process must be carried out for each run on the job. The more information the engineer provides on the print, the faster the installation will progress. Remember, the object of this planning walkout is to prevent the entire pulling crew from being idle while the lead technician tries to track down the engineer or superintendent for clarifications or additional information. REVIEW QUESTIONS 1. The most accurate method of measuring for conduit pulls is a. from a set of prints. b. field measurements taken with a wheel. c. measuring with a pull tape.

7 CHAPTER 12 PLANNING THE INSTALLATION How much extra cable must be added to make a fusion splice in a manhole? a. 30 feet b. 1 percent c. 30 feet for each side of the splice d. 10 feet 3. Subdividing larger conduits with innerducts a. efficiently uses duct space. b. allows for future expansion. c. offers additional protection to the fiber optic cable. d. all of the above 4. The purpose of a planning walkout is to a. get a rough idea of the installation. b. measure the conduit run. c. clarify all the final details. d. none of the above

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