Transmission and distribution lines are key components in providing electrical service to residences and com-mercial, industrial and institutional power customers, and constructing and maintaining them requires trained and experi-enced crews using the right equipment.
This report covers equipment and accessories used to install aerial and underground electrical cable—it does not include equipment needed for outside communications plant construction, although some of the equipment—reel carriers and trailers, for example—can be used on both power and datacom products.
For overhead power line construction and maintenance, basic equipment includes reel stands, reels and trailers equipped with reel carriers; pulling and tensioning devices; rollers and stringing blocks; cable grips and swivels; and various support accessories, which depend on the job’s needs.
Underground cable is either placed in conduit or directly buried. Conduit may be in an excavation or trench or installed by the trench-less method of horizontal directional drilling. As with aerial work, reels—often mounted on trailers—are used for underground installa-tions. Underground pulling equipment ranges from compact, manually operated rodders to powerful underground pullers with an air component to propel pull rope through the duct. The cable pulling process often is assisted by pushing equipment to reduce the pulling force necessary.
Electrical contracting companies may do the excavation or directional drilling to place conduit in the ground with their own crews or subcontract that portion of the job and then have their electricians install the conductor and complete other electrical work.
Four leading suppliers of outside plant cable installation equipment discuss industry trends.
Bill Caulkins, vice president of sales and marketing for the Sherman & Reilly power division, said the basic equipment for string-ing overhead transmission lines on a typical project includes an overhead pulling device on one end, a tensioning device on the other to control movement and position, and the rollers and stringing blocks that the conductor passes through.
“On the transmission side,” Caulkins said, “there is a trend for power companies to increase current-carrying capabilities at the same voltages—either with larger conductors or smaller conductors per phase. That may require different equipment than is used for single conductors. For example, tensioners have to have greater capacities to handle a larger number of conductors per phase.”
Conductor manufacturers, Caulkins said, also are experimenting with new conductors that will not sag when heat is generated, and new materials cannot bend over a sharp radius and, therefore, require a block with a larger diameter.
“We are working with conductor manufacturers in development of equipment to install these new cables,” he said.
For aerial distribution, Caulkins said a trend in equipment is to make greater use of hydraulics on pullers and tensioners. This makes them safer on the pulling end if something goes wrong. They also operate more smoothly on the tensioning end.
For underground distribution, a basic difference includes the use of steel pulling cable rather than synthetic rope that is used for aerial work.
“Air is used to blow a ‘bird’ through conduit to drag the pulling cable inside the conduit,” Caulkins said. “Hydraulically powered twin capstan, multigroove wheels pull the conductor through the conduit. Relatively new are pushers that assist the puller on long cable runs, and there is a trend to use self-powered combination equipment with the compressor and blowing options all on one trailer. The trailer can be dropped at the work site, and one man can do everything safely and economically.”
Al Crandall, director of cable placing systems for A-D Technologies (Arnco equipment for underground cable installations), said a growing number of utilities are using cable in conduit (CIC).
“This is a process in which the conduit is extruded around the cables during manufacturing,” he explained. “This eliminates the need for pushing or pulling in new installations and can be installed by open trench, directional drilling and plow chute installations.”
Siliconized lubricants, prelubricated pull tapes, and profiled prelubed high-density polyethylene ducts have had a significant impact on techniques for pushing and pulling cables—the more friction that can be reduced, the greater the distance cable can be pushed or pulled.
“URD cable pushers,” Crandall said, “improve productivity and reduce installation costs because a cable pusher can set up in one lo-cation and push in several conduits. [There is] no need to move equipment each time. Also, a cable pusher puts less stress on a cable than when pulling.
Underground Electric Cable
Putting power distribution cable underground is nothing new. For decades, service lines and sometimes feeders in new residential de-velopments and commercial industrial and government complexes have been buried. Power customers like the absence of overhead wires, and buried cables are protected from ice and windstorms.
However, it has become time to replace much of this underground infrastructure; some of it has been in the ground for 30 years or more. At the same time, those who live and work in areas with buried utilities expect them to stay that way; in-stalling new utility poles and aerial conductors would be expensive and unacceptable to customers. However, making extensive excavations to put in new cable isn’t acceptable to them, either.
The challenge is to economically reconductor aging buried cable without extensive damage to surface improvements that have been added since the old cable was installed.
Although actual costs can vary widely, the industry consensus is that it costs more to bury cable than to place it over-head; there are the costs of conduit and equipment and labor to bury it. While putting power cable underground elimi-nates the need for some of the equipment to string aerial cable, it requires equipment to install the underground conduit and to run cable through it.
For reconductoring underground cable in urban areas, the method of construction used by most power providers is the trenchless construction procedure of horizontal directional drilling (HDD). Compact drill units make a precisely guided pilot hole, then pull cable back through the hole or install conduit into which cable is placed. If cable preinstalled in con-duit is used, the cable installation step is skipped, speeding construction.
Permanent cable lubrication permits removal and replacement if necessary.
Compact HDD equipment requires a small job-site footprint. The bore usually is initiated from the surface and exits at a point where it will be connected to the system or a structure. The bore path can go under streets, driveways, sidewalks, lawns and flower beds, and other improvements, greatly reducing surface damage and restoration costs. In most cases, it isn’t necessary to close streets to traffic.
Some electrical contractors have invested in HDD equipment and operate it with their own crews; others subcontract that portion of the work. Cobb EMC, Marietta, Ga., has been reconductoring services by directional drilling since the first HDD equipment became available in the early ’90s, and today does the work both with its own crews and equipment and with subcontractors.
The most common conduit for electrical projects is HDPE (high-density polyethylene). Smaller diameters used for feeders or services come on reels, so depending on the length of an installation, fusing pipe is not necessary. PVC conduit also is used, and PVC pipe with restrained joints is well suited for installation by directional drilling.
Although cost prohibits large-scale replacement of existing aerial cable with underground cable, some utilities do have ongoing programs to convert older neighborhoods from overhead to underground.
Crandall said installing conduit by directional drilling, compared to aerial applications, may allow smaller puller and pusher units to be used because of reduced frictional properties.
Eric Cope, product manager at Condux International, said that, at times, demand for cable installation has been greater than in pre-vious years.
“Installation techniques are the same as they were 20 years ago,” Cope said, “but the equipment has been designed to be safer and more efficient. Changes include lighter weight pullers for better mobility, pulling eyes that can be installed faster and more easily, and the use of pushers to help move cable through conduit.
“Integrated foot pedals allow the operator to stand off to the side of the puller. This keeps them out of the path of the rope, in case the rope were to break. Easier and quicker setup saves labor costs, and greater mobility allows them to use the pullers in more areas. Electronic recorders allow the customers to know their pulling tensions so they do not damage the cable by over-tensioning.”
Direct burial of cable can reduce the amount of equipment needed because cable is not placed inside conduit.
Brian Beavers, sales manager for TSE International, said there is a trend of growth in the number of transmission projects that is expected to continue for the next few years. This trend is generating demand for larger equipment, such as 80,000-lb. pullers.
“There also is an emphasis on green construction methods, particularly in the West,” Beavers said. “An example of a response to that is chassis mounted PTO-driven equipment to eliminate an engine and, therefore, reduce emissions.”
GRIFFIN, a construction and tools writer from Oklahoma City, can be reached at firstname.lastname@example.org.