Download
1 / 214
2.14k likes | 2.31k Views
OBJECTIVES. 1. Explain why the ability to pull longer lengths of cable has decreased installation times and labor costs. 2. Differentiate between the installation techniques of pulling cable versus blowing cable. 3. Define the terms “tensile strength” and “jam ratio.”
E N D
OBJECTIVES 1. Explain why the ability to pull longer lengths of cable has decreased installation times and labor costs. 2. Differentiate between the installation techniques of pulling cable versus blowing cable. 3. Define the terms “tensile strength” and “jam ratio.” 4. Describe the importance of the coefficient of friction with regard to cable installations. 5. Explain the difference between straight conduit pulls and pulls through bent conduit from the standpoint of COF usage. 6. Demonstrate how to calculate the jam ratio for a three-cable pull. 7. Given the inner diameter of the conduit and the outer diameter of the cable, determine the likelihood as to which configuration a three-cable pull will assume. 8. Contrast between water-based and silicone-based pulling lubricants. 9. Describe the negative aspects of using mini-roller lubricants for cable pulls through multiple-bend conduit.
In reality, there are a few more complications involved, such as: Neither the cable nor the conduit is flat. More than one cable may be pulled, complicating the dynamics between the rubbing surfaces. Pulls are not conducted through totally straight conduit, adding forces other than gravitational weight into the equation, especially at the conduit bends.
If the conduit is straight, with no bends, the equation used is: Tout = Tin + LWµ where Tout is equal to the tension out, Tin is equal to the tension in, L is equal to the length of the straight run, W is equal to the weight of the cable (per length), and µ is equal to the COF.
If the conduit contains bends, and consideration is taken for the nongravitational forces in the conduit bends, the equation used is: Tout = Tineµq where Tout is equal to the tension out, Tin is equal to the tension in, e equals the natural log base (approximately 2.71828), µ equals the COF, and q equals the angle of bend.
The formula for the calculation of the jam ratio for a three-cable pull is: J = 1.05 ID/OD where J is equal to the jam ratio, ID equals the interior diameter of the conduit, and OD equals the outer diameter of the cable. The factor of 1.05 takes into consideration the fact that the conduit assumes a more oval shape at the bends.
The idea is to prevent the change of positions between the cables where they roll over each other and jam. However, the following questions remain. What are the exact ranges of jam ratios that indicate pulling problems? What constitutes an accurate COF for three-cable pulls? What is the optimal conduit feed position for three-cable pulling? What if the conduit already contains cable that is functioning properly?
LAB 19 OBJECTIVE Pulling CAT5 Cable To properly pull CAT5 cable through multiple sections of conduit, and test the resulting run
TIP This may seem to be a rather lengthy piece of cable, but keep in mind that a length of at least 16 feet is required for several of the tests that are conducted on CAT5 cable by the Level II testers. This gives you leeway for recovering from any wiring errors that may occur and still have enough length left to take meaningful Level II measurements.
TIP Figure 6-6 displays the conduit layout for the simulator grid panel. You will use this layout for lab procedures that will follow, so it is important to locate the PVC sections exactly as shown in Figure 6-6. The diagram is accurate regarding the rows (50) and columns (180) of openings in the grid panel. If necessary, you may use it to ensure an accurate layout of the PVC conduit sections.
TIP These numbers represent the row (from top to bottom) and column (from left to right) coordinates for the ½-inch, 10-24x pan head machine screws (Phillips). These screws thread through the ½-inch mounting brackets, the grid panel, and then into the wing nuts. Obviously, the wing nuts tighten the brackets down to hold the PVC sections into place. Conduit 1 is one of the 3-piece sections you just assembled.
TIP Leave enough play in the conduit bracket assembly to make small adjustments. If you tighten the first wing nut too far, the second machine screw may not reach through the grid panel far enough to start the second wing nut.
TIP Try to leave some play in the assembly at this point, if possible. Once the remaining bracket is mounted, you may tighten the section of conduit down.
TIP Conduit section 6 will be the remaining 3-piece combination you assembled earlier.
TIP If you discover any deviations between Figure 6-6 and your assembly, take the time to make the necessary corrections before moving on.
TIP As the fish tape protrudes through each section of conduit, guide it to the opening in the next section. The layout of conduit you have installed represents an installation requiring two separate cable pulls. Real-world installations may involve multiple pulls within the same lengths of conduit. In an effort to reduce the buildup of friction, your layout involves two pulls using the same cable. In the event that the friction becomes a critical factor at your site (due to variations in conduit type, cable jacket type, temperature, and so on), apply lubricant to the cable as directed by your product’s manufacturer.
TIP The following guidelines should be kept in mind whenever you are using fish tape: Protect the fish tape from contacting live circuits or from inadvertent bending by keeping it in its reel when not in use. Periodically check the fish tape for damage such as cracks, rust, sharp bends, nicks, or gouges. These types of flaws can cause the tape to break under the stress of a pull.
TIP The following guidelines should be kept in mind whenever you are using fish tape: Protect the fish tape from contacting live circuits or from inadvertent bending by keeping it in its reel when not in use. Periodically check the fish tape for damage such as cracks, rust, sharp bends, nicks, or gouges. These types of flaws can cause the tape to break under the stress of a pull.
TIP The following guidelines should be kept in mind whenever you are using fish tape: (continued) Because a large amount of tension can build up during a cable pull, always maintain an adequate recovery posture in case this tension is suddenly released while pulling. Keep away from trip or landing hazards while controlling a cable under tension. If pulling cable through conduit containing existing cable, check to be sure that none of this wiring is under power during the pull.
TIP The following guidelines should be kept in mind whenever you are using fish tape: (continued) Never try to create a bend at the end of cold fish tape for pulling purposes. The steel will fracture unless it is torch heated (red hot) before a bend is made. Avoid creating sharp bends in fish tape being pulled. If such a bend appears in fish tape you are using, cut the end off below the bend, and reform the end using a torch.
TIP The following guidelines should be kept in mind whenever you are using fish tape: (continued) When heating fish tape with a torch, allow the tape to cool completely before using it. Fish tape can be damaged or broken if used with slip joint or locking pliers.
TIP The practice of pulling twine through the conduit, along with the cable being installed, is a universal courtesy extended to other cable installation workers who may do follow-up work once the initial installation has been completed. It allows the pulling of another cable through the conduit at some later date. It would then be expected that more twine would be pulled through at that time for the next job, and so on.
TIP Once the cable has been secured to the fish tape, it’s ready to be pulled. At this point, the pull rating of the cable itself must be considered. If this value is exceeded during a pull, the cable itself may be damaged and rendered useless for its intended purpose.
TIP The simulator grid panel should be securely mounted at this point, and any lubricant that may be required should have been applied as directed by your instructor.
TIP The following tips should be kept in mind during a cable pull: If trouble occurs on an installed cable run, pull a new wire rather than splicing the defective one. If a spliced cable must be used, never locate it behind a wall or some other area where it cannot be reached. The general pulling limit for 4-pair UTP cable is 25 pounds. For STP cable the limit should be kept below 55 pounds.
TIP The following tips should be kept in mind during a cable pull: (continued) On long cable runs through conduit, it is not recommended to pull cable through more than two 90-degree bends at once. This suggestion should not, however, prevent you from successfully pulling CAT5 UTP cable through the conduit layout in this lab procedure. Avoid pulling cable through more than 100 feet (30 meters) of conduit at one time.
TIP The following tips should be kept in mind during a cable pull: (continued) Provide support for every 5 feet of cable in order to prevent the strain on hanging cable from supporting its excess weight. Avoid conditions that result in sharp bends in the cable. For 4-pair UTP cable, the bend radius limit is 4 times the cable’s diameter. Avoid stepping on the cable at all times while you work around it.
TIP The following tips should be kept in mind during a cable pull: (continued) Protect the outer jacket of the cable from stress such as staple fasteners or over-tightened cable ties. Keep the cable run away from sources of electrical noise such as electrical motors or fluorescent lights. When using conduit, leave a pull cord in the conduit with the pulled cable, so that more cable can be pulled at a later time.
TIP The following tips should be kept in mind during a cable pull: (continued) Keep cable pulls away from heat sources such as heat ducts and hot water pipes. Try to avoid fire barriers or thick layers of insulation when installing cables by locating a run through the inner walls. Maintain the tip and ring polarity designations for all connections.
TIP Try to estimate how much force you are using during the pull, so as not to exceed the 25-pound tension limit.
TIP You’ll want enough twine to provide two feet beyond the bottom-right end of conduit 7.
TIP Once again, the simulator grid panel should be securely mounted at this point, and any lubricant that may be required should have been applied as directed by your instructor.
TIP You should arrange this activity in such a way that if you pulled cable the first time, while your partner steadied the grid panel, the roles are switched so that your partner pulls cable this time.
