CONSTRUCTION PRACTICES Aerial

Transcription

1 CONSTRUCTION PRACTICES Aerial INTRODUCTION Sound installation practices should be followed during construction of an aerial plant. The purpose of this section is to highlight the unique mechanical design of MC 2 cable and to outline certain practices for successful installations. During the process of building an aerial plant, many different construction techniques will be required. This section will describe construction methods for proper installation of coaxial cables lashed onto strand and installation of messengered cable. Before going into the field, make sure that all tools and equipment are in proper working order. A preventative maintenance program is a good idea for all mechanical items in order to save time and expense for the contractor and/or system operator, regardless of the installation method. BACK PULL METHOD The back pull method of coaxial cable installation is the most widely used and the recommended method for aerial installation. This method can be used successfully with any size or number of cables, even in locations where poles are not easily accessible. First insure that all equipment is in good working order. Check the maps for the day s installation of trunk and feeder cable to determine the proper footages. After the reels are selected, make sure that the cable has been tested for fault and proper length as described in the testing section. The cable ends on the reel must always be capped. If reels have been stored outside and the cable ends have not been capped, the cable must be retested. Installing improperly stored cable can be costly and should be avoided. When loading reels onto the trailer, make sure that the cable pay off is from the top of the reel. This will provide a smooth incline from the reel trailer to the cable chute. Always install reel brakes and the appropriate spacers along with the reels (figure 6-). Check to see that cable ends are fastened to prevent loosening during transportation to the installation site. When starting an unfamiliar cable route, walk or drive along the cable run beforehand to check for trees, bad poles or make ready. Also check for 90 or 45 turns along the cable route. When encountering a 0 to 45 turn, use a 45 corner block (figure 6-2) and with turns greater than 45, use a 90 corner block (figure 6-3). These blocks are necessary to prevent any mechanical damage when pulling corners. No more than two 90 turns should be pulled on any run. After the cable route has been walked or driven out, it is time to proceed with the installation. Position the trailer in line with the strand at a distance of twice the strand height from the pole Figure 6-. Reel Brakes Figure degree Corner Block Figure degree Corner Block (figure 6-4) and chock the trailer wheels to prevent movements when the cable is pulled. Next, check reel flanges for nails or staples that could damage the cable during pay off. As the cable is pulled off of the reel, adjust reel brakes so that the reel will not continue to turn if pulling is ceased. Attach a cable chute or 45 block at the first pole location to support the cable through the transition angle from the reel to the pole. At this point, mount a cable puller onto the strand, pull the cable over the chute, and attach the puller with a pulling grip. Swivels and/or thrust bearings should be used to relieve twisting. 6-

2 MC 2 coaxial cables can be pulled by hand, truck or winch. The maximum pulling tensions and minimum bending radii for MC 2 cables are listed below. Size Minimum Maximum Bending Radius Pulling Tension lbs lbs lbs lbs lbs. Figure 6-5. Roller As the cable is pulled over the cable chute towards the next pole, position rollers at 25 to 50 foot intervals to provide support. This will prevent the cable from bouncing while the pulling starts and stops and eliminates mid-span damage. Also, a roller must always be attached at each pole location after the puller is repositioned from one side of the pole to the other to prevent the cable from coming in contact with the pole (figure 6-5). These practices should be carried out through the entire cable pull. When the cable route has been completed, the lasher should be filled with lashing wire and ready for the crew member at the last pole. If multiple cables are being installed, use a cable positioner to provide uniform positioning and lashing of the cable. Also, a cable block pusher should always be used between the lasher and the positioner, and ahead of the positioner to uniformly guide the cable from the rollers to the lasher. In the case of single cable installation, when the positioner is not used, only one block pusher is needed (figure 6-7). As the lasher is pulled across a span, the block pusher will move all rollers ahead of the lasher. Remove the collection of rollers and lasher accessories at each pole. Cut the lashing wire and temporarily clamp it to the strand. Then reposition the lasher and accessories to the other side of the pole in order to continue the lashing operation. Once this is done, securely fasten the temporarily clamped lashing wire with a lashing wire clamp and position a band and spacer on the strand to prevent the lashing wire clamp from rubbing the cable. When forming the expansion loop, use a loop forming tool, leaving the tool in place while the lasher is prepared for the next span. At this point the lashing operation begins while the cable and expansion loop tool are held in place to prevent any pull out of cable from the loop. After pulling the lasher to the next pole, remove the tool and proceed with the installation of bands and spacers to prevent the cable from rubbing against lashing wire clamps and pole hardware and to hold expansion loops in place (figure 6-6). cable chute roller spacing cable puller feet Trailer placement at twice strand height Figure 6-4. Aerial back pull 6-2

3 TECHNICAL NOTES CONSTRUCTION PRACTICES Aerial Trilogy Figure 6-6. Band and spacer placement Breakaway swivel rated at maximum pulling tension Figure 6-7. Drive off Pull off approximately 3 feet of cable to provide slack for equipment splicing. All exposed cable ends are to be capped at all times and should be pointing downward. Before leaving the location, check the cable for any damage that may have occurred during the pulling operation. Continue these procedures from pole to pole until the final span is reached, at which point the excess cable on the reel should be taken up as the final span is lashed. Always cap the ends of any cable that is left on the reel. DRIVE OFF METHOD When using the drive off method to install cable, follow the same procedures for selecting reels and loading the trailer as previously described for the back pull technique. To begin the drive off method, first mount the lashing equipment on the strand. This equipment will consist of a cable chute or guide, a pusher, a multiple cable positioner, a second pusher and the lasher, in that order. This sequence of accessories will provide uniform lashing and will lessen the chances of mechanical deterioration. If only a single cable is to be lashed, the multiple cable positioner and one of the pushers will not be necessary (figure 6-7). Once the lashing equipment is in position, move the truck and cable trailer to about 50 feet from the starting pole or approximately two times the strand height. Pull the cable from the reel back to the 6-3

4 first pole, feed it through the lashing equipment and secure. Then fasten the lashing wire to the strand so that the drive off procedure can begin. The pulling vehicle and trailer should always remain approximately 50 feet from the lashed cable to assure a smooth incline from the trailer to the cable guide. When the lashing equipment reaches the next pole, cut the lashing wire and temporarily clamp it to the strand. The lashing equipment can now be transferred to the other side of the pole but be careful not to damage the cable. After the lashing equipment has been mounted on the opposite side of the pole, form an expansion loop if necessary. As with the back pull method, the loop forming tool should remain in place until lashing resumes and the lasher is pulled to the next pole. At this point the tool can be removed and the lashing wire clamps, cable straps and spacers can be attached in the same fashion as previously described for the back pull method. Continue the drive off procedure in this manner until the last pole in the run is reached. If an extra length of cable is required for equipment splicing, the tail should extend beyond the pole approximately 3 feet. All exposed cable ends must be capped and should be pointed downward. Caps are available upon request. Before leaving the location, inspect the cable for any physical damage. Note: With this method, pulling tension and axial or rotational tension cannot be monitored on the cable. This method has a tendency to allow the expansion loops to twist after lashing. LASHER SET-UP AND OPERATION As with any construction equipment, the lasher must be checked before each day s use to insure that it is in good working order. Since smooth operation of the lasher is vital for successful construction, it must be well maintained. This may require tightening of loose parts, replacement of broken or worn ones and periodic oiling as recommended by the manufacturer. There are a variety of lashers on the market that can be used for MC 2 installation. Since each type of lasher offers different features, choice must be based on specific needs. However, one feature that is recommended is a braking mechanism which prevents the lasher from slipping back when pulling is stopped. Most lashers are equipped with this feature. The lasher must first be loaded with the appropriate lashing wire according to the manufacturer s specifications. Check the lashing wire to ensure that it pulls easily from the lasher. Open the lasher pulling rope Figure 6-8. Lasher set-up 6-4

5 gates and strand locking mechanism and place the lasher over the strand and cable. With the lasher in position, close the strand locking mechanism to prevent the lasher from falling, then close and adjust the lasher gates so that the gate rollers ride snugly against the cable. Tie the lashing wire to the lashing wire clamp and tie the pulling rope to the lasher (figure 6-8). The lashing machine can be pulled either by hand or by truck. If using a truck, maintain a slow and even speed for best results. With either method the lasher should be pulled down and to the side in order to maintain uniform tension and lashing. When a pole is reached at the end of each pull, check the amount of lashing wire to ensure an adequate supply for the next span. Since a lashing wire splice may rub the cable, all lashing wire ends must be terminated using a lashing wire clamp. Although some different equipment is required, multiple cables can be installed in the same manner as previously described for back pull and drive off techniques. For the pulling of multiple cables, a multiple reel trailer, multiple cable puller and multiple rollers should be used to maintain proper orientation between the cables. For the lashing operation, it is necessary to use a lashing machine that can accommodate the size and number of cables being installed. A multiple cable positioner should also be used to facilitate uniformity of lashing. Multiple cables should always be double lashed. In addition to multiple cable installations, double lashing is highly recommended for highway crossings and spans greater than 200 feet. Following these procedures will provide for the establishment of a mechanically sound and uniformly lashed plant. GROUNDING & BONDING - Aerial The primary purpose of grounding is to provide a path for any fault currents to be neutralized, thus to safeguard employees and the public from injury. The following definitions come from the NEC Grounded Effectively or Effectively Grounded - Intentionally connected to earth through a ground connection or connections of sufficiently low impedance and having sufficient current carrying capacity to prevent the build up of voltages that may result in undue hazards to connected equipment or to persons. Bonding - The permanent joining of metallic parts to form an electrically conductive path that will insure electrical continuity and the capacity to conduct safely any current likely to be imposed. Grounding and bonding hardware will vary with different methods. Some of the following practices are taken from the NESC. 2 Local codes or ordinances should also be followed. Multi-current carrying conductors (such as high voltage power) within close proximity of each other can induce unwanted fault currents on other non-current carrying conductors. The cable carrying strand (CATV Plant) is constantly subjected to these unwanted fault currents. High power surges and lightning can also cause induced voltages and currents to be present. Maintaining proper clearances and using good grounding and bonding techniques will provide a means of reducing and dissipating these fault currents to a zero ground potential. For a CATV plant to be Effectively Grounded the National Electrical Safety Code requires there to be no less than eight bonding and or grounding connections per mile. If a vertical utility ground does not exist, a ground rod must be driven. Bonding Clamps There are two categories of bonding clamps, one for similar metals and one for dissimilar metals. A bronze split bolt is usually used when a copper to copper bond is made. For dissimilar metals, a bi-metal clamp is used with one side for galvanized steel or aluminum and the other side for copper. Multi-purpose clamps are also available which allow bonding of similar and dissimilar metals (figure 6-9). Figure 6-9. Bonding clamps A regular strand bonding clamp may be used to bond galvanized steel strand to itself. When strand and guys are not continuous, a continuity bond should be used. Splicing of the bonding wire should be avoided. Ground Rods Ground rods or grounding electrodes should be a minimum of eight feet in length and 5/8 inches in diameter, and have a conductive and non-corrosive outer surface. Driven ground rods should be buried to a depth of eight feet at or below ground level. When driving ground rods, always maintain a minimum of ten feet from pipelines carrying any flammable liquids or gases. For the purpose of grounding coaxial cable, existing electrodes may be used National Electrical Code 2 National Electrical Safety Code 6-5

6 under the proper circumstances, otherwise made electrodes must be driven to ground the cable. Existing Electrodes - Consist of conducting items installed for purposes other than grounding. Some examples of existing electrodes include metallic water piping systems or steel reinforcing bars in concrete foundations and footings. CATV Strand Existing Utility vertical ground wire Bonding Clamp Made Electrodes - Should penetrate permanent moisture levels below the frostline. The surface will be conductive and must be made of metal or combinations of metals that do not corrode excessively under the existing conditions for the expected service life. One example of a made electrode is a driven rod, usually made of copper or copper clad. Ground Wire The pole ground -The ground wire or grounding conductor provides a path for any fault current from the CATV Plant (strand/cable) to the grounding electrode or ground rod. Use a minimum of No. 6 AWG copper wire to connect the galvanized steel strand to the existing utility vertical ground wire. When bonding to an existing ground wire, the two copper wires may be connected with a single bonding clamp or split bolt, but a bi-metal clamp should be used to connect the strand to the bonding jumper (figure 6-0). When an existing utility vertical ground is not available it may be necessary to install one. Ground wire should always be run as straight as possible and any bends should be made gradual. Use copper coated or copper clad staples to secure the ground wire to the wooden pole, thus preventing any corrosive reaction between the grounding conductor and the staple (figure 6-). Install a covering or molding over the first eight feet of the ground wire to provide protection to the public and prevent any mechanical damage. A ground rod clamp is used to attach the copper ground wire to the copper clad grounding electrode, usually made of bronze. In any case, the clamp must be corrosion resistant. EXPANSION LOOPS Expansion loops are a common means for absorbing the effects of thermal expansion and contraction in the cable plant. It is recommended that expansion loops in MC 2 coaxial cables be formed into 2 inch flat bottom loop design for cables up to and including.750 and 5 inch for inch cables. This loop has been extensively tested in the research lab and in field applications with complete success. This design distributes strains across the flat section rather than concentrating them at any single point. It is recommended that expansion loops be placed at every pole throughout the plant. For trunk cables we suggest that a loop be placed on each side of amplifiers, passive devices and splices. It is also recommend that expansion loops not be formed at the pole but Bonding Jumper #6 AWG Copper Wire Split Bolt Existing 8 ft. Ground Rod, 5/8" diameter Figure 6-0. Bonding to existing ground rod CATV Strand Bonding Clamp #6 AWG Copper Wire 8 ft. Ground Rod, 5/8" diameter Figure 6-. Bonding to new ground rod rather on each side of a pole. Expansion loops that are placed directly at the pole can be damaged from excessive contact with the pole or pole hardware. When forming expansion loops in multiple cables, straps should not be used in the bottom of the loops. Additional loops may be needed in certain climates. National Electrical Safety Code 6-6

7 When coaxial cable is installed on the strand, pay attention to tensioning and sag limitations (See Sag and Tension Section). In most instances the construction should match the amount of sag given to telephone and power cables. The proper amount of sag can provide more cable in the span and create more room for expansion and contraction. This practice will supplement the use of expansion loops for reducing maintenance problems caused by cable expansion and contraction. Expansion loop forming tools come in an array of designs ranging from simple contoured boards to mechanical bending machines. Many of these tools can be used to form a flat bottom loop on MC 2 cables. Note: Expansion loop forming tools are recommended for consistent formation of the expansion loop. Procedures for their use are available from the manufacturer. Since these are available in a variety of different sizes and features, a choice must be made based on the particular need of a system. Two of these tools will be described in this section. Jackson Cable Bender The Jackson cable bender is available in two sizes. The smaller tool can be used to form loops in MC 2 coaxial cable up to and including the.750 size. The larger tool is used for the.00 size. To form a loop, open the action of the bender completely and mount the tool on the strand. Then place the cable onto the shoes and crank the ratchet down until it reaches the stop. The action of this device is such that the loop is formed by the application of Figure 6-2. Lemco expansion loop tool downward pressure of the shoes at each end of the flat 2 inch section, while the cable is supported by two other shoes at each outside end. Leave the tool in place if lashing is to resume. After the lasher is pulled to the next pole, open and remove the tool. Lemco Expansion Loop Tool The Lemco expansion loop tool (figure 6-2) is available in two sizes. The smaller tool is used for MC 2 coaxial cable up to and including the.750 size. The larger tool forms a 5 inch flat bottom loop for the.00 size. This tool operates in a similar manner as previously described, but the action is different in that pressure applied to the inside radius of the loop is constantly moving. See figure 6-6 for the recommended band and spacer placement for expansion loop geometry. Pole spans Less than 200 should incorporate one expansion loop per pole (figure 6-3). Pole spans greater than 200 should incorporate two expansion loops per pole (figure 6-4). Less Less than 200 feet feet Figure 6-3. Less than 200 feet - one expansion loop per pole Greater Greater than than feet feet Figure 6-4. Greater than 200 feet - two expansion loops per pole 6-7

8 SAG & TENSION Proper sag and tension during cable installation maximizes cable plant life. Referring to Figure 6-8, sag is defined as the mid-span deviation (d) from a straight line, divided by the span distance (L), expressed as a percent. For example, for d = 36 (or 3 feet) over a span of 50 feet, the sag is (3/50) x 00%, or 2%. Tension refers to the tension in the strand which is required to produce a given sag condition. The recommended sag for combined cable and strand is 2% at a temperature equal to the mean climate temperature. The three equations below are used to calculate sag and tension as a function of span length, and combined weight of cable(s) and strand. The recommended procedure for achieving desired sag is as follows:. Set initial strand sag slightly less than the target value, since adding the weight of the cable (later) will increase the sag. 2. Place strand in the pole clamps, free to adjust tensions for final recommended sag of 2%. 3. Adjust strand tension to achieve final sag value after cable is lashed to strand. Adjust tension for each span of cable. 4. A dynamometer or equivalent device can be used to check strand tension at any point in the procedure. Because of the effects of thermal expansion and contraction, sag will vary with temperature. Sag will increase slightly on hot days and decrease slightly on cold days. This means that temperature at the time of the sagging operation must be taken into account. The first example of how temperature is accounted for during the sagging operation is provided in figure 6-9a, where a single.500 Bare MC2 cable is double lashed on /4 EHS steel strand. Assume the span is 00 feet and the mean annual temperature is 70 F. The objective is to achieve the recommended sag of 2% when the outside temperature is 70 F. But suppose the sagging operation is being done on a very cold day when the outside temperature is only 30 F. Referring to the upper table in figure 6-9a, the proper sag to install under these conditions would be only 2inches. Then, as the temperature warms to 70, thermal expansion will automatically result in a sag equal to the desired 24 inches. The lower table in figure 6-9a shows the strand tension values for the corresponding sag conditions. Note that the effects of 0.5 inch of ice () are shown in the far right columns of figure 6-9a. Figures 6-9b through 6-9h provide additional examples of various cable and strand combinations, intended for a 70 F mean climate temperature, with sag of 2%, and showing what sag to use if the sagging operation occurs at a different temperature. Other factors which should be taken into account for proper sagging include: Normal daily temperature extremes (0 to 30 F). Normal annual temperature changes (20 to 60 F). Extreme annual temperature changes (60 to 40 ). Solar heating on bare aluminum can be as high as 20 F. Jacketed cable can be as high as 40 F above ambient air temperature. 2% 70 F L=50 feet d=36 inches Figure 6-8 Sag example 6-8

9 The examples provided in figures 6-9a through 6-9h are for mean annual temperatures of 70 F. Sag and tension tables for other cable and strand combinations, and for other mean annual temperatures can be generated by computer program ( SAG ) available on computer disc (IBM compatible). Contact Trilogy Applications Engineering Department for information on obtaining the SAG program disc, or if there are other questions related to recommended sag procedures. SAG AND TENSION TABLE CABLE AND STRAND SAG (inches) - no wind 0 F 0 F 30 F 50 F 70 F 90 F 20 F STRAND TENSION (pounds) - no wind 0 F 0 F 30 F 50 F 70 F 90 F 20 F , , ,994 Figure 6-9a. Recommended sag and tension vs. installation temperature for 2% sag with an annual mean temperature of 70 F. Cable installed with /4 ESH strand-all cable double Bare 6-9

10 SAG AND TENSION TABLE CABLE AND STRAND SAG (inches) - no wind 0 F 0 F 30 F 50 F 70 F 90 F 20 F STRAND TENSION (pounds) - no wind 0 F 0 F 30 F 50 F 70 F 90 F 20 F , , , ,8 Figure 6-9b. Recommended sag and tension vs. installation temperature for 2% sag with an annual mean temperature of 70 F. Cable installed with /4 ESH strand-all cable double lashed. 2@ MC2.500 MC2.750 Bare 6-0

11 SAG AND TENSION TABLE CABLE AND STRAND SAG (inches) - no wind 0 F 0 F 30 F 50 F 70 F 90 F 20 F STRAND TENSION (pounds) - no wind 0 F 0 F 30 F 50 F 70 F 90 F 20 F , , , ,995 Figure 6-9c. Recommended sag and tension vs. installation temperature for 2% sag with an annual mean temperature of 70 F. Cable installed with /4 ESH strand-all cable double lashed. 2@ MC2.650 MC2.750 Bare 6-

12 SAG AND TENSION TABLE CABLE AND STRAND SAG (inches) - no wind 0 F 0 F 30 F 50 F 70 F 90 F 20 F STRAND TENSION (pounds) - no wind 0 F 0 F 30 F 50 F 70 F 90 F 20 F , , , ,903 Figure 6-9d. Recommended sag and tension vs. installation temperature for 2% sag with an annual mean temperature of 70 F. Cable installed with /4 ESH strand-all cable double MC2.500 MC2.650 MC2.750 Bare 6-2

13 SAG AND TENSION TABLE CABLE AND STRAND SAG (inches) - no wind 0 F 0 F 30 F 50 F 70 F 90 F 20 F STRAND TENSION (pounds) - no wind 0 F 0 F 30 F 50 F 70 F 90 F 20 F , , , ,064 Figure 6-9e. Recommended sag and tension vs. installation temperature for 2% sag with an annual mean temperature of 70 F. Cable installed with /4 ESH strand-all cable double MC2.500 JAU 6-3

14 SAG AND TENSION TABLE CABLE AND STRAND SAG (inches) - no wind 0 F 0 F 30 F 50 F 70 F 90 F 20 F STRAND TENSION (pounds) - no wind 0 F 0 F 30 F 50 F 70 F 90 F 20 F , , , , ,020 Figure 6-9f. Recommended sag and tension vs. installation temperature for 2% sag with an annual mean temperature of 70 F. Cable installed with /4 ESH strand-all cable double lashed. 2@-MC2.500 JAU 6-4

15 SAG AND TENSION TABLE CABLE AND STRAND SAG (inches) - no wind 0 F 0 F 30 F 50 F 70 F 90 F 20 F STRAND TENSION (pounds) - no wind 0 F 0 F 30 F 50 F 70 F 90 F 20 F , , ,73 250,72,40,08, ,27 Figure 6-9g. Recommended sag and tension vs. installation temperature for 2% sag with an annual mean temperature of 70 F. Cable installed with /4 ESH strand-all cable double lashed. 2@-MC2.650 JAU 6-5

16 SAG AND TENSION TABLE CABLE AND STRAND SAG (inches) - no wind 0 F 0 F 30 F 50 F 70 F 90 F 20 F STRAND TENSION (pounds) - no wind 0 F 0 F 30 F 50 F 70 F 90 F 20 F , , ,63 250,099,069, ,9 Figure 6-9h. Recommended sag and tension vs. installation temperature for 2% sag with an annual mean temperature of 70 F. Cable installed with /4 ESH strand-all cable double JAU 6-6

17 OVERLASHING Overlashing is a method of hanging cable on a strand with existing cable already lashed to it. It is primarily used to replace old or damaged cable in a system that has already been activated. Overlashing may also be used in instances where it would be impractical to remove other cables from the strand in order to add new cable, such as rebuilds or upgrades. Due to the binding effect that the existing lashing wire creates, it is necessary to use a roller that does not lock to the strand. This devise will hang on the strand and or cable. It supports the cable and reduces the pulling tension during the cable installation. The best rollers for overlashing are the type that lock around the cable and strand without locking to the strand itself. It is advisable to increase the roller spacing from the normal 50 foot spacing in order to reduce the chance of rollers binding as the lasher pushes them. Also, pay attention to supporting the cable when selecting the roller placement. The method for pulling cable for an overlash is similar to a normal pull, except there is no room for a cable puller to ride on the strand. In this case, the best method for pulling is to attach a long rope to the cable with a pulling grip and then pull the rope through the rollers. In order to give ample support to the cable as it is being pulled, the rope should always be laid over any roller immediately preceding the cable before it is pulled, with proper back tension maintained. Once the cable is in place, set up the lashing machine. The lashing procedure for an overlash is the same as a normal back pull lash except that it will be impossible to use a cable block pusher or a multiple cable guide due to the existing cable on the strand. Use caution when opening and closing the lasher gates since the gates are the only mechanisms preventing the lasher from falling. Once the gates have been closed, they should be adjusted to the proper tension and the lashing wire should be attached to the strand. Make sure to maintain proper tension should lashing be stopped in order to free or remove a cable block. During the lashing operation, the cable should remain as tight as possible. This can be achieved by turning the reel in order to take up slack as the lasher is pulled. This will straighten the cable, which in turn will provide straight entry into the lasher and help insure tight wrapping of the lashing wire. When constructed in this manner, an overlashed cable can look and perform just as well as the cables that were originally lashed to the strand. MESSENGERED CABLE INSTALLATION Figure 8 Cables Messengered (or figure 8 ) cable is installed in a manner quite different from lashed type construction. As messengered cable (cable with built-in strand) is attached to the poles, tension and sag limitations must be observed. Creating expansion loops and slack for splicing will also demand a different approach. Messengered cable should only be installed in areas requiring a single cable. BACK PULL METHOD Figure 8 Cables The back pull method for messengered cable begins by setting up the reel in the same manner as previously described in back pull techniques for lashed construction. Install a pole chute bracket and a 45 corner block on the first pole to allow for the angle of cable inclination, then attach pole hardware to all poles on the cable run and messenger cable blocks at all required poles by using a 6 inch length of /4- inch steel rod attached to the suspension clamps. The type of cable block designed for this purpose will straddle the suspension clamp and hang from the rod on each side in order to stay in place (figure 6-5). Cable blocks are only required at points of stress when J hook hardware is being used. Figure 6-5. Messenger block Length of /4 steel rod Once all rollers and hardware are in place, attach a pulling grip to the messenger on the reel of cable and a pull line to the grip. Then pull the cable span by span over the rollers. It will be necessary to release tension at pole locations in order to lay the pull line over the J hooks or rollers. 90 and 45 cable blocks should be used on all turns in the pull and no more than one 90 turn should be pulled at a time. Use caution so that the low hanging cable is not hit by passing traffic. Use additional rollers as necessary. After reaching the end of the run, attach the strand to the hardware of the last pole (figure 6-6). Attach a pulling line to the messenger with a strand grip about 20 feet from the first pole. Then pull the line across the rollers of the 45 block in order to tension the cable and take up slack on the reel. After the cable has been partially tensioned with the rope, use a chain hoist to complete the tensioning and raise the cable to a safe working height. 6-7

18 Using a chain hoist with two strand grips, provide the necessary slack for the equipment to be spliced. Place the grips on each side of the section where slack is needed and tighten the hoist until slackening begins. Then cut the cable away from the messenger between the two grips, and remove the necessary section of strand with bolt cutters. When slack for splicing is being created, the amount of strand cut away should equal the amount of excess cable desired. When making slack for expansion loops, remove the amount of strand equal to 75% of the loop s depth. After the length of messenger is removed, install a strand splice and release tension on the messenger. It may be necessary to relieve tension at the first pole during this process due to the increase in tension created by removing strand. After all slack and expansion loops have been created, the messenger tension can be adjusted for proper sag and then permanently attached at the first pole. Once this is done, remove all rods and cable blocks and secure the messenger to the suspension clamps. NOTES DRIVE OFF METHOD Figure 8 Cables The drive off method for messengered cable begins by placing pole hardware on all poles in the run. Attach cable blocks wherever necessary in the same manner as described for the back pull method. Then drive the vehicle and trailer 50 feet ahead of the first pole. After attaching the messenger from the reel to the hardware of the first pole, pull the vehicle forward down the run so that the tension causes the cable to unreel. When the vehicle is about 50 feet past the next pole, stop pulling and release the tension by backing up. Raise the cable with a cable lifting tool, and place it on the cable block. Use caution to insure that the low-hanging cables are not hit by passing traffic (figure 6-7). When the vehicle passes the end of the run, use a chain hoist at the last pole to tension the cable to a safe working height. Once this is done, create the expansion loops and finish the job in the same manner as previously described for the back pull method. Note: When using the drive off method, pulling tension and the speed of the vehicle must be monitored closely. GROUNDING AND BONDING Figure 8 Cables All guy wires and messengers of the self-support cable must be bonded together using a No. 6 AWG copper wire. (Refer to section on Aerial Grounding and Bonding for more details.) There must be a minimum of eight grounded and or bonded connections per mile to the existing verticals. 6-8

19 messenger block pull line/winch pulling grip pull line wheel chocks twice strand height at pole Truck moves 50ft past pole then backs up to allow cable to be lifted to messenger block Figure 6-6. Messenger Back Pull Figure 6-7. Messenger Drive-off 6-9

20 Vertical Clearances of Communications Cables from Supply Conductors and Equipment* SUPPLY CONDUCTOR OR EQUIPMENT REQUIRED CLEARANCES. Conductor, 0 to 8700 volts inches 2. Conductor, > 8700 volts inches plus 0.4 inches per KV above 8700 volts 3. Conductor Case (non-grounded), 0 to 8700 volts inches 4. Conductor Case (effectively grounded), 0 to 8700 volts inches 5. Conductor Case (non-grounded), > 8700 volts inches plus 0.4 inches per KV above 8700 volts 6. Conductor Case (effectively grounded), > 8700 volts inches 7. Transformer Case (non-grounded), 0 to 8700 volts inches 8. Transformer Case (effectively grounded), 0 to 8700 volts inches 9. Transformer Case (non-grounded), > 8700 volts inches plus 0.4 inches per KV above 8700 volts 0. Transformer Case (effectively grounded), > 8700 volts inches. Street Light Bracket (non-grounded) inches 2. Street Light Bracket (effectively grounded) inches *Supply conductors and equipment are located above the communications cables. (Source: National Electrical Safety Code) Vertical Clearances of Wires, Conductors and Cables above Ground, Roadway, Rail or Water Surfaces** (Non-insulated communication conductors, supply cables or 0 to 750V, meeting rules 230C2 or 230C3) SURFACE Where wires, conductors or cables cross over or overhang: REQUIRED CLEARANCES. Track rails of railroads (except electrified railroads using overhead trolley conductors) feet 2. Roads, streets and other areas subject to truck traffic feet 3. Driveways, parking lots and alleys feet 4. Other land traversed by vehicles, such as cultivated, grazing, forest, orchard, etc feet 5. Spaces and ways subject to pedestrians or restricted traffic only feet 6. Water areas not suitable for sailboating or where sailboating is prohibited feet 7. Water areas suitable for sailboating including lakes, ponds, reservoirs, tidal waters, rivers, streams, and canals with unobstructed surface area of: a. Less than 20 acres feet b. Over 20 to 200 acres feet c. Over 200 to 2000 acres feet d. Over 2000 acres feet 8. Public or private land and water areas posted for rigging or launching sailboats clearance above ground should be 5 feet or greater than in 7 above, for the type of water areas served by the launching site. Where wires, conductors or cables run along and within the limits of highways or other road right-of-ways but do not overhang the roadway: 9. Roads, streets or alleys feet 0. Roads in rural districts where it is unlikely that vehicles will be crossing under the line feet **Source: National Electrical Safety Code: Rule