Safe and efficient cable pulls begin in the planning. If inadvertently released, potential forces could run amok and harm workers or civilians or damage the conductors, so cable pulls require careful attention before and during the physical process.
(To preclude risk of civilian injuries if working in occupied space, block access to the areas where the pull starts and where it ends.)
Pulling devices matched to the specific task and proper pulling techniques and strategies help ensure both the wire and workers come through the task intact.
Don’t cut corners when pulling cable. For maximum assurance of safety and highest level of efficiency, electricians should always use high-quality equipment such as rope, wire puller, and cable feeders if needed, as well as grips and baskets, etc. This equipment should be appropriately sized to the particular pull and checked for integrity. Because there is some fiber tear in every pull and ropes get stiff with age, check your ropes ocasionally. For maximum tensile strength in a particularly critical pull, “use a new pulling rope,” recommended Bernie Hengels, national accounts manager, Rothenberger, USA, Inc.
When setting up a pull through steel, aluminum, or PVC conduit for copper wire, anchor the wire-pulling equipment securely so there will be no movement under stress.
(Point of reference: when pulling fiber optic cable, which cannot be stressed as much as standard copper conductors, use only a cable puller rated specifically for that type of fragile cable. These cable pullers often will not exceed 600 pounds of pulling strength but pull a lot faster than copper cable ones.)
For copper cable pulls, if the system itself does not otherwise provide adequate stability during the pull, use a floor mount accessory where appropriate (in perhaps 50 percent of pulls) that is designed to be bolted or otherwise held onto the floor and that will provide a proper secure base to mount or hold down the cable puller. Some systems do not use bolts but rather rely on booms.
If cable length dictates, feeders and pullers should use walkie talkies to maintain communication throughout the pull. It is prudent to position an experienced electrician with a clear view of the tension gauge at the pull end of the rope (if there is one) to control the potential forces, and be within quick reach of the “on/off” switch. This person should have a sharp eye to catch any overlapping of the rope on the capstan, a trained ear to interpret the sounds of the motor as it pulls, and know when to increase tension on the pull rope and when to let up a little, Hengels said.
The type of rope and its tensile strength are extremely important. Some manufacturers recommend that the rope should have a minimum rope safety factor of four to one (rope average breaking strength compared to maximum pull force by the cable puller) with a minimum of rope exposed.
For example, if you are using an 8,000-pound capacity cable puller, you want a rope to have a minimum safety factor tensile strength of 32,000 pounds. “And if more than the minimum of pulling rope is exposed, then use an even higher safety factor,” suggested Ken Hagemeyer, director, product manager, Greenlee Textron.
For high-force cable pulling, many manufacturers suggest using double-braided polyester rope that inherently has “low stretch” and stores less energy than other types of rope. “You don’t want to use a rope that can store energy during the pull like a stretched rubber band, because if it breaks, it could snap back in backlash and possibly injure someone,” said Hagemeyer. Double-braided polyester rope has a high strength-to-size ratio, meaning you get a four-to-one safety factor and smaller diameter rope, he pointed out.
Keep as much rope as possible within the conduit so that if the rope breaks or any other part of the pull system fails, the stored energy in the rope is almost all confined within the conduit.
When selecting pulling equipment accessories such as sheaves and pulling grips, “Use the pulling capacity of the cable puller as the determining tool selection factor, rather than base the tool selection on the force needed to do the pull,” Hagemeyer advocates. “Otherwise, if the cable puller capacity is greater than the rope capacity and something jams, the rope can break before the safety device on the cable puller shuts down the puller.”
Factors that determine rope size include length of run, number and size of conductors being pulled, and how many turns the conduit has, noted Hengels. There cannot be more than 360 degrees between boxes in a pull. If the turns exceed 360 degrees, an intermediate pull box is required.
For optimally efficient pulls that carry as little risk as possible of damaging cable on its route, start with clean, dry conduit. Between the time of installation and the time for the wire pull—which could be months—the conduit may have been filled with rain water or contaminated, damaged, or deformed by forces other than those under your control.
To ensure that the conduit is not obstructed or kinked and is burr free and debris free after any collected water has been blown or vacuumed out, use a sturdy wire duct brush or a flexible mandrell that cleans the pipe of sand, grit, dirt, or other contaminants, ensuring clear passage.
If you are spreading a lubricant ahead of the pull, do so with a lube spreader swab after that first through passage. Don’t skimp on cable lube while reducing the strain on the cable and the overall pulling force needed; it also reduces the strain on the accessories. Most lube is water-based and won’t harm the conduit or the conductors.
The cable lube puts a film on the outside surface of the insulation, easing the tension between the insulation and the inside wall of the conduit and helping prevent the insulation from stretching or tearing. “If pulling cables in weather below freezing, use special, glycol-based lubricants that won’t freeze up and solidify in the line,” Hengels suggested.
Make sure you use baskets and grips that are appropriately sized for the wire and are rated for the maximum pulling capacity of the puller. Ditto for grips, making sure there is a four-to-one rated capacity. Don’t force a larger grip onto a smaller-size wire, nor the converse, because either way you lose the rating of the grip and could lose the load. Also, never attach the grips to the cable jacket because they could slip off during use. You get a much better grip when you strip back the insulation and attach directly to the conductor.
To prevent the wire from stretching or breaking during the pull, don’t exceed the cable tension as recommended by the cable manufacturer. Pulling apparatus manufacturers sell special cable tension chart recorders that give accurate readings of the maximum tension placed on conductors and provide printouts that certify that the wires were not overstretched to satisfy specification requirements.
For maximum efficiency, use a cable puller with the appropriate capacity for the pull, and not appreciably more, suggested Hagemeyer. “The bigger the equipment, the slower it pulls,” he pointed out. “Larger pullers pull more slowly than smaller ones because you are only working with 120 volts and 15 or 20 amps, and you have to develop gear ratios using that much power. An 8,000-pound capacity puller might pull at 8 to 9 feet per minute, whereas a 4,000-pound capacity puller will pull up to 15 or 16 feet per minute.”
Never stand in line behind the cable puller. If the rope snaps, you want to be out of line from both the rope and the possible recoiling of the equipment. Sometimes the equipment itself is designed to protect the tool operator. Most pullers, including those below, have some sort of ratchet mechanism that permits the capstan to rotate only in a forward direction, and build in a variety of other safety attributes.
The Greenlee Textron 6800 series UltraTugger, rated for 8,000 pounds for example, featuring a digital readout of the forces, an audio alarm high-force warning and a circuit breaker shut off at maximum force, has a right angle sheave that allows the operator to stand out of the direct line of force and yet maintain a tailing force on the rope.
Gardner Bender Brutus Powered Cable Puller, delivering up to 8,000 pounds pulling power from the one-direction planetary gear-design motor, features a load read-out meter that warns of hung-up cable or other excessive conditions. Frame mount supports a virtually unlimited number of set-up configurations.
Rothenberger USA E-440-84 Heavy-Duty Two-Speed Power Cable Puller, with a pulling capacity of 8,000 pounds, sports three safety features: one-way anti-backlash bearings that allow the shaft of the capstan to turn in one direction only and prevent backward rotation if the chain breaks, a “ratchet safety dog” to prevent backward slippage of capstan during temporary shut-down, and a chain designed to break and fail at 8,000 pounds. A read-out meter tells of force and amps during pulling, keeping the operator informed if the puller is reaching overload conditions.
The portable Condux International, Inc. CableGlider Plus Cable Puller features a self-tailing capstan for added stability, two pivoting arms for a variety of optimized pulling positions, and a foot switch for operator convenience and safety. The unit, which includes a retaining fork for stabilizing and does not have to be anchored, comes with a two-speed removable power pack providing up to 6,500 pounds of pulling force at low speed.
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