The tools and techniques used to run outside-plant cable differ greatly from those used inside buildings.
Patrick McLaughlin
For many cabling-plant managers, the different worlds of inside-plant and outside-plant (OSP) cable collide right in their own backyards-literally. A campus cabling-plant design incorporates the cabling inside multiple structures and the cabling that connects those structures to each other. And in some respects the two different media types-inside and outside cable-are different disciplines.
With inside cable, concerns include such characteristics as plenum or nonplenum rating. With outside cable, on the other hand, the ability to stand up to harsh weather conditions is a consideration. Also, OSP cables often run for longer distances than their indoor counterparts, frequently mandating that owners use fiber-optic as opposed to twisted-pair copper cabling. "Most large campuses I've seen use singlemode fiber instead of multimode fiber because of the distance between buildings," says Anthony Minichiello, owner of OSP consulting firm Maximis Communications Consultants (Concord, NH).
Likewise, the method of putting OSP cabling into place differs greatly from inside-plant cabling placement. In fact, according to Minichiello, customer-owned OSP cable placement strongly resembles cable placement in the public network. "OSP cable placement involves very similar equipment, techniques, and personnel, whether it's customer-owned or part of the public network," he continues.
He points out that many organizations owning their own OSP cabling are large facilities such as university campuses, airports, and military bases. "I've worked on some military bases that are larger than some of the towns I've worked in," he notes. "So to see the contractors installing the cable, you really wouldn't be able to tell if they were installing customer-owned or public plant cable simply by looking at the methods they're using and the equipment they have."
Winches, capstans, and sheaves
For underground cable placement, the equipment used to get conduit and reeled cable from point A to point B typically includes winches, capstans, and sheaves. The winch is the actual pulling mechanism, and these tools differ from each other by such performance characteristics as pulling force, storage capacity, and pulling speed. Physical characteristics like size and weight are also important, partly because the winch is one of several cable-placement tools often found mounted to a trailer or the back of a truck. Most underground-placement setups include some combination of truck and trailer, or perhaps both, at each end of the pull. So the manner in which this equipment is mounted to a truck or trailer is also a factor to consider.
Capstans typically come into play when contractors place fiber-optic cable because fiber cable can withstand only so much pulling tension and bend. A relatively recent product introduction by General Machine Products (GMP-Trevose, PA) was designed specifically to work with existing winches. The company's fiber-optic mid-assist capstan limits pulling tension to 600 lbs and maintains a 25-inch working diameter. The company says this diameter translates into good pulling speed-650 ft/min-at 100 rotations per min, whether the contractor is pulling rope, muletape, or fiber-optic cable. A smaller version of the tool is designed to be used as an end-puller but can be converted for mid-assist pulling when used with the company's capstan conversion reel.
A sheave is a pulley with a circumferential groove for holding the cable in place during pulling. The groove size determines the cable or rope size that the sheave can accommodate. Sheaves are typically used to change the direction of a pull and can be used for underground or aerial cable placement. Like other OSP cable-placing equipment, sheaves are often mounted to trailers or trucks.
Aerial placement
Although underground cable placement is often the preferred method, sometimes aerial placement is necessary. "Underground and aerial placement methods are fairly equally used in customer-owned OSP environments," explains William Pfundt, GMP's president. "The placement environment affects the method chosen. In new construction, for example, putting ducts underground makes sense. But with existing buildings, installing ducts becomes more expensive, requiring a method such as directional boring. Aerial cable placement has some downsides, such as aesthetics and leaving the cable exposed to the elements. That's not as impactful with short-run distances, but it can be with longer runs. If aerial cable already exists, then piggybacking is the least costly alternative."
According to Pfundt, if an OSP environment is not the huge facility type referenced earlier in this article by Maximis's Minichiello but is a much smaller environment, then placement becomes much easier, and placement equipment becomes much less of an issue. "Sometimes in a smaller environment the cable can even be pulled by hand, with the assistance of a capstan," Pfundt explains.
However, when such hand placement is not possible in an aerial environment, Pfundt says lashing is the most widely implemented method. Often, a lasher will lash a cable to a support wire that runs between poles. However, self-supporting cable- cable that does not need a support wire-has also been available for some time.
Lashers are distinguished from one another by several characteristics, including the cable sizes they accommodate, lashing-wire capacity, and factors that affect setup procedure.
GMP's Apollo lasher, which has been available for about a year, allows installers to lash cable onto self-supporting cable, which Pfundt says was impossible before. The issue is weight, he points out. The Apollo lasher itself weighs less than 39 lbs, so it can be used to lash lightweight cables such as fiber and coaxial cables onto self-supporting cable. Contrast that with trying to lash a twisted-pair copper cable that includes several hundred pairs, and it's easy to see why lashing over self-supporting cable, without the need to install a support wire, is a technological advancement. The Apollo accommodates cables and ducts up to 4 inches in diameter.
Cable blocks
Another tool used in aerial placement is the cable block. Used as part of the lashing process, cable-placement blocks support the cable or cables being placed. The blocks themselves often contain sheave-like pulleys and can support one or several cables during installation.
Another type of block-the corner block-helps in environments where cable is not placed in a straight line. For example, corner blocks from Jameson Corp. (Clover, SC) are available in 60°- and 90°-angle styles. The blocks mount to poles and are designed to evenly distribute pressure on the cable when pulling around corners. The company says its corner blocks are completely compatible with competitive setup brackets.
Regardless of the size, shape, location, or owner of an OSP cabling system, safety during its installation and of the finished product are paramount, concludes Maximis's Minichiello. "The National Electric Safety Code is the letter of the law for any cable that is placed outside of a building," he explains, "regardless of who owns the infrastructure. The NESC acts as guidelines and codes for outside cable. That's an important fact for all contractors and plant owners to know."