In outside-plant installations, conduit is normally installed underground to safeguard cables from damage as well as facilitate cable placement for fast and future needs. You can even install Conduit Fittings inside buildings to facilitate pulling cable between two points including from the telecommunications closet (TC) to be effective-area outlets, or from an equipment room to your TC. To safeguard, isolate, and identify the cables, innerduct–often known as subduct–may be installed inside existing larger-diameter conduit.
Conduit is identified as a rigid or flexible metal or nonmetallic raceway by which cables may be pulled. Additionally, although conduit can be used to house various types of cable, the National Electrical Code (NEC) uses the expression “optical fiber raceway” in Article 770 to illustrate conduit, or raceways, for optical-fiber cable. Various kinds conduit can be found, for example electrical metallic tubing (EMT), rigid metal conduit, PVC, fiberglass, and versatile conduit. For premises installations, how-ever, metal flexible conduit is just not recommended because of potential abrasion problems for the cable jacketing.
Metal conduit, which typically comes in 10-foot lengths, is pretty rigid and requires special tooling and accessories to sign up with it. Nonmetallic conduit can be obtained on reels in longer, continuous lengths that do not have to be joined as much.
“The only problem with installing EMT conduit is it requires a special skill set and training, together with plenty of practice–or you wind up making swing sets,” explains Kevin Smith, project manager at MTS Services (Bedford, NH). “Metal conduit will come in 10-foot lengths so you should do any nonstandard bends by hand, and that`s where the technician`s special skill is necessary.”
Arnco Corp. (Elyria, OH) sells innerduct for the cable-TV, telecommunications, and electric utility markets, says Tom Stewart, electrical products sales manager. “Inside a building, several types of duct are utilized–by way of example, riser- and plenum-rated–but all of our products are produced from thermoplastic materials, including polyvinylide fluoride [pvdf] and polyvinyl chloride [pvc]. The thermoplastic materials are easier to install than metal.”
You can find three various sorts (or ratings) of innerduct: outdoor, riser-rated, and plenum-rated. Robert Jensen, engineering manager at Endot Industries Inc. (Rockaway, NJ), explains: “Outdoor is generally polyethylene and it`s certainly not rated. Then there`s a riser product, rated by Underwriters Laboratories [UL], which can be generally a thermoplastic material like polyethylene or PVC with fire-retardant chemicals put into it. Along with the third sort of duct is UL plenum-rated, generally a pvdf product, which can be fire-retardant and smoke-resistant,” says Jensen.
In accordance with Mike D`Errico, regional director of sales at Pyramid Industries (Erie, PA), most products that conduit and innerduct manufacturers make is for outside plant. Some manufacturers offer prelubricated innerduct and conduit, “fairly often incorporating some sort of silicon,” he says. “For premises cabling, Pyramid delivers a plenum raceway (tested to UL-910) along with a riser raceway (UL-1666) for installation in vertical shafts.” Furthermore, the riser product is halogen-free which is often useful for military, shipboard, or tunnel applications, based upon the specifications.
Obviously contractors install conduit where building codes require it, but also in which the cabling system needs physical protection or defense against unauthorized access.
“We use conduit in riser and backbone systems in the building entrance to the main distribution frame,” says Karl Clawson, senior v . p . and partner, Clawson Communications (Greenwood, IN). “So we also set it up for horizontal cabling, especially in university campuses. Within the living quarters, we install cable in conduit because it allows the cable extra protection, and hopefully, keeps it all out of students` reach,” he says.
Some cabling contractors would rather have other trades install conduit; for example, electricians who may have more experience with performing this. “Generally, the only real time we use Plastic Flexible Conduit occurs when we`re developing a riser or penetrating a fire wall,” says Smith. “Typically, we would not install conduit from your wiring closet for the workstation outlet. In short distances, as much as 100 feet, we will install conduit between buildings dependant upon the existing infrastructure.
Besides the traditional smooth-bore type, innerduct is available by using a ribbed inner wall to lower friction in between the cable sheath and also the innerduct wall. “A wave-rib within the duct reduces surface contact between your cable as well as the wall of the duct, thus lowering the coefficient of friction and enabling you to pull cable over longer distances,” says Stewart.
Another variation is definitely the multicelled conduit system, that offers outerducts with pre-installed innerducts. Clawson says that, because of its cost, his company does not use conduit with pre- installed innerduct. “We keep leftover conduit available to work with on other jobs,” he says. “But pre-installed conduit is actually a special application, so overages and underages are kind of costly to deal with.”
For premises applications, Dura-line (Knoxville, TN) has designed a conduit, known as Hex-line, for multiple-duct applications between buildings. “While you pull the ducts from the reel (two to each and every reel), they go into a collector, which Dura-line supplies cost-free,” says Ray McLeary, v . p . of sales. “Each duct includes a men and women part, which can be snapped together, building a multiple duct system. This saves time, space, and cash, but the most crucial savings is space.” He explains: “Normally, you can put three 1-inch innerducts in a 4-inch conduit. With this system, it is possible to fit four 11/4-inch or six 1-inch innerducts into the conduit.”
When choosing innerduct, you also need to be worried about its tensile strength and crush resistance. “The thicker the wall material, the greater the tensile rating,” says Stewart. “If you`re likely to pull it across a long-distance, choose a wall thickness that lets you pull the duct over that distance. The crush-resistance feature helps to ensure that the innerduct won`t be damaged during the placing process–or maybe you can`t pull in the cable,” he explains.
Because of the limited amount of tensile pull that one could exert about the cable, people search for ways to decrease the coefficient of friction inside the conduit. “You can find products on the market including prelubricated conduit,” says Stewart. “And there`s a good different technology used for placing cable, generally known as air-blown fiber (or ABF), the location where the fiber-optic cable is blown to the conduit. We manufacture what we should call the `air-trak` system–a conduit system with chambers–for use in ABF installations.” [Air-blown fiber is available in america from Sumitomo Electric Lightwave Corp. (Research Triangle Park, NC).]
Conduit and innerduct have one important thing in common: They facilitate pulling or replacing a cable for additional capacity within a premises cabling system. However, every contractor recognizes that for an installation grows, the quantity of cables grows to fill all the space from the conduit. Therefore, selecting the correct trade size is important, because you must leave sufficient clearance between your walls of the conduit along with other cables (start to see the eia/tia-569 standard). Typically, conduit trade sizes range between 1/2 to 6 inches in diameter. Minimum conduit size suggested for backbone cables is 4 inches. Sufficient clearance must be offered to allow pulling the cable without excessive friction or bending.
The NEC conduit-fill tables define the total amount (being a percentage) of different types of cable you may use in the conduit. “The NEC typically covers power cables,” says Stewart. “With good-voltage cables, you need to consider temperature and impedance, which really don`t apply when it comes to data cables in conduit. The real question for data cable is: Are you able to pull it into how big duct that you`ve selected?”
“The most significant decision when installing conduit is the size of the conduit and clearance from the wall,” says Clawson. For external use, we use 4-inch PVC conduit, and we try and install all the conduit inside the trenches when we can for future use.”
Cables are continually included with conduit systems which are often filled to capacity with generations of older cable. When new cables are added, friction and pulling tension may damage existing cables inside of the conduit. One way to provide for future changes would be to subdivide larger conduits with innerducts, that happen to be smaller in diameter than conduit, generally nonmetallic, and semiflexible.
“In a existing structure, many installers do not want to pull new cable on the cable already inside the conduit,” says Stewart, “since they risk damaging the current cable. To optimize a larger conduit, they`ll install several smaller innerducts inside it. They`ll pull a reduced fiber cable into among the innerducts, then have additional ducts for use for future cable placement.”
Innerducts are classified by outside diameter (OD) whereas trade-size conduits use inside diameter (ID). One-inch innerduct is often used within buildings; however, 11/4-, 11/2-, and 2-inch innerducts are available for larger fiber cables. Although innerducts take up space inside a conduit, they offer additional protection and suppleness in constantly changing cabling installations.
“Generally, if you`re installing a 4-inch conduit,” says Smith, “you`ll wind up putting in three 1-inch innerducts: one for fiber, one for data, and another spare. What you want to do is pull just as much dexlpky51 you may at installation time.”
Typically constructed from thermoplastic materials, innerduct features a pull string already installed. It is available in ribbed-, corrugated-, and smooth-wall styles. Some types have prelubricated inside walls. These special coatings as well as the physical properties from the inner wall of your innerduct ensure less friction and tension when pulling cable.
“Corrugated innerduct can be used in plenum and riser products,” says D`Errico. “And, when created from high-density polyethylene, it really is typically utilized for short–1000 feet or less–installations.” Smooth wall is used for direct-buried, trenching, plowing, aerial, and directional boring applications. “The Metal Flexible Conduit is the cable jacket is “lifted” far from and contains a smaller region of connection with the pipe, decreasing the coefficient of friction. Although the principle is: the greater the hole, the easier it`s will be to pull the cable,” he says.
According to Clawson, “We use ribbed innerduct if we`re pulling one innerduct, because it`s simpler to handle. If we`re pulling through a directional boring machine and it`s a multiple pull, then we use smooth innerduct. It really is simpler to pull smooth innerduct on top of an even surface, and it doesn`t kink as easily as ribbed innerduct.”
When using innerduct, it is very important verify whether it be a plenum or non-plenum area and to install the innerduct with all the appropriate support. If the innerduct is secured with tie wraps inside a plenum area, only take plenum-rated products.
Innerduct is generally offered in one color–orange for your fiber-optic communications industry. Color is often installation-specific; for instance, one color for data cable, one for telephone, and so on. “There is a movement afoot to try to use color designations for various types of applications,” says Stewart. “Orange is generally communications, red can be for electric power, and yellow for gas.”