Appendix 4 Don t Get Hurt Pulling Cable
Appendix 4 Don t Get Hurt Pulling Cable Don t Get Hurt Pulling Cable Here are some tips on pulling cable safely (Reprinted from CEE News dated June, 1990) There are plenty of ways to pull cable improperly. The high amount of pulling tension involved invites danger to workmen and damage to equipment - even with the best setup. The following information from two cable puller manufacturers represents the very basics of cable pulling. For more detailed and complete information, please read the manufacturer s instruction manuals. Safe and efficient cable pulling requires a through understanding of the operation of the puller and accessories, and professional judgment. According to Greenlee Textron Inc., the demanding nature of the process is related to four characteristics: 1. Virtually every cable pulling application is unique with wide ranging differences. Therefore, only trained, experienced persons should be responsible for the setup and operation of a cable pulling system. Preplanning will assist in conducting a safe pull. 2. Forces as high as 16,000 lbs may be developed at a point in the pulling system. 3. Enormous amounts of elastic energy are stored (rubber band effect) in the pulling rope. Stretched, exposed rope can whip violently when broken. 4. Control of cable pulling forces may be lost. Failure of any one of the system components, such as rope, chains, attachment structure, grips, sheaves, etc., could result in loss of control of cable pulling forces. Capstan Theory The capstan is a force multiplier. The resultant pull force produced by the operator s tailing force is dependent on the number of wraps of rope around the capstan. These figures are based on a coefficient of friction of 0.125 which is approximately the expected value of polyester multiplex and double braided polyester ropes. When a number of full wraps of rope around the capstan are used, for example, small operator tailing forces produce large pull forces. Only 20 lbs of operator tailing force will produce 1,024 lbs of pull force when five full wraps are used. The operator s feel (tactile feedback) will be more sensitive with fewer wraps. This gives the operator control over the pull. The resistance of a cable changes during pulling for Appendix 4 Page 1
Hayward Electric Injury & Illness Prevention Program various reasons. The slip/stick behavior, frictional resistance, vertical and horizontal, element and length of pull are principal reasons for the fluctuations. The operator continually adjusts his tailing force to account for these changes. During normal pulling operations, when there is no operator tailing force, the slip/stick friction of the rope and the capstan will not be enough to allow any significant build up of pulling force. Therefore, no tailing force produces no pull force. This means that the operator is in complete control. The pull can be stopped by relaxing the tilting force, a safety feature unique to capstan pulling. If the capstan rotates while the rope is stationary, both rope and wear and increased temperature will occur, possibly causing the rope to break. Do not hold a load or maintain a stationary rope on a rotating capstan. Switch off the motor and hold the tailing end of the rope or wrap the tailing rope around the combination cleat/handle or tie the tailing end of the rope to an external structure. Planning the Pull Preplanning the pull can lessen the danger and ensure the likelihood of a safe, successful pull. Here are some of the considerations. How long should each pull segment be? Which direction should you pull from and to? Is the conduit or raceway sized properly to meet the NEC codes? Is there enough room for personnel to work safely? Is communication clearly established between members of the pulling crew? Are load ratings proper? Do your pulling system components act as force multipliers? Are the structural elements to which the pulling system components will be attached of sufficient strength? Is sufficient manpower available for a safe pull? Basic Safety Guidelines Gary Janquat, business development manager, GB Electrical Inc. offers the following guidelines for safe cable pulling. Appendix 4 Page 2
Appendix 4 Don t Get Hurt Pulling Cable 1. Ensure that the cable puller has been safely secured. The setup should be done and selected by a qualified person, either the superintendent or the assigned safety person. 2. Protect the cables themselves. Follow the cable manufacturer s guidelines, which state maximum allowable tension on the conductors. Janquart says the use of a tension meter in-line is important. The tension meter measures line pull in pounds and tells the operator how much tension is being put on the conductors. It also gives the operator a window to the system. It tells him if there are any restrictions during the pull so he can shut down the puller before damage can occur. 3. The cable must be lubed properly. A good grade of lubricant should be used on the cable to allow the least amount of resistance of friction on the cable jacket inside the conduit run, says Janquart. 4. Calculations to determine maximum line tension should be completed by taking into account the type and size of conduit used, the distance the wire or cable is traveling, how many degrees of bend are in the run, and by determining the size and number of cable to be used. 5. Once proper calculations have been made, ensure that the cable puller has enough power to make the pull, and very importantly, determine the correct type and strength of rope to use. We recommend using a doublebraided polyester. The less expensive polypropylene rope does not have the pulling strength of polyester. The rope should be rated at least as strong as the working load needed-not the tensile strength indicated. 6. The rope should also be kept in good working condition. Inspect the rope for wear and damage before each use. If it shows signs of wear, replace it. 7. The operator should never stand directly behind the rope capstan; if a rope fails, it can recoil with lethal force. Appendix 4 Page 3
Hayward Electric Injury & Illness Prevention Program Appendix 4 Page 4