In outside-plant installations, conduit is usually installed underground to guard cables from damage and also to facilitate cable placement for immediate and future needs. You may also install Conduit Fittings Wholesale inside buildings to facilitate pulling cable between two points such as in the telecommunications closet (TC) to function-area outlets, or from an equipment room to a TC. To protect, isolate, and identify the cables, innerduct–often known as subduct–might be installed inside existing larger-diameter conduit.
Conduit is described as a rigid or flexible metal or nonmetallic raceway through which cables may be pulled. Moreover, although conduit enables you to house various kinds of cable, the National Electrical Code (NEC) uses the word “optical fiber raceway” in Article 770 to describe conduit, or raceways, for optical-fiber cable. Various kinds conduit are available, like electrical metallic tubing (EMT), rigid metal conduit, PVC, fiberglass, and flexible conduit. For premises installations, how-ever, metal flexible conduit will not be recommended as a result of potential abrasion problems for the cable jacketing.
Metal conduit, which typically will come in 10-foot lengths, is fairly rigid and needs special tooling and accessories to join it. Nonmetallic conduit is accessible on reels in longer, continuous lengths that do not must be joined as frequently.
“One problem with installing EMT conduit is it demands a special skill set and training, in addition to a great deal of practice–or you find yourself making swing sets,” explains Kevin Smith, project manager at MTS Services (Bedford, NH). “Metal conduit comes in 10-foot lengths so you need to do any nonstandard bends by hand, and that`s where the technician`s special skill is needed.”
Arnco Corp. (Elyria, OH) sells innerduct on the cable-TV, telecommunications, and electric utility markets, says Tom Stewart, electrical products sales manager. “In the building, several kinds of duct are used–for example, riser- and plenum-rated–but all our products are manufactured from thermoplastic materials, including polyvinylide fluoride [pvdf] and polyvinyl chloride [pvc]. The thermoplastic materials are simpler to install than metal.”
There are actually three different types (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 not necessarily rated. Then there`s a riser product, rated by Underwriters Laboratories [UL], that is generally a thermoplastic material for example polyethylene or PVC with fire-retardant chemicals included in it. Along with the third sort of duct is UL plenum-rated, generally a pvdf product, that is fire-retardant and smoke-resistant,” says Jensen.
In accordance with Mike D`Errico, regional director of sales at Pyramid Industries (Erie, PA), most products which conduit and innerduct manufacturers make is for outside plant. Some manufacturers offer prelubricated innerduct and conduit, “very often incorporating some kind of silicon,” he says. “For premises cabling, Pyramid offers a plenum raceway (tested to UL-910) plus a riser raceway (UL-1666) for installation in vertical shafts.” Moreover, the riser product is halogen-free and is often useful for military, shipboard, or tunnel applications, based upon the specifications.
Naturally contractors install conduit where building codes require it, and also the location where the cabling system needs physical protection or protection from unauthorized access.
“We use conduit in riser and backbone systems from the building entrance on the main distribution frame,” says Karl Clawson, senior vice president and partner, Clawson Communications (Greenwood, IN). “And that we also do the installation for horizontal cabling, especially in university campuses. From the living quarters, we install cable in conduit mainly because it affords the cable extra protection, and hopefully, keeps it of students` reach,” he says.
Some cabling contractors would rather have other trades install conduit; for example, electricians that have more expertise in performing this task. “Generally, really the only time we use Plastic Flexible Conduit is when we`re constructing a riser or penetrating a fire wall,” says Smith. “Typically, we would not install conduit in the wiring closet on the workstation outlet. In short distances, around 100 feet, we would install conduit between buildings according to the existing infrastructure.
As well as the traditional smooth-bore type, innerduct is accessible by using a ribbed inner wall to lessen friction involving the cable sheath along with the innerduct wall. “A wave-rib on the inside of the duct reduces surface contact involving the cable as well as the wall of the duct, thus decreasing the coefficient of friction and letting you pull cable over longer distances,” says Stewart.
Another variation is the multicelled conduit system, which provides outerducts with pre-installed innerducts. Clawson says that, due to the cost, his company will 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 a special application, so overages and underages are form of costly to handle.”
For premises applications, Dura-line (Knoxville, TN) has designed a conduit, called Hex-line, for multiple-duct applications between buildings. “When you pull the ducts away from the reel (two to every reel), they enter into a collector, which Dura-line supplies totally free,” says Ray McLeary, v . p . of sales. “Each duct includes a female and male part, which are snapped together, building a multiple duct system. This saves time, space, and money, but the most significant savings is space.” He explains: “Normally, you are able to put three 1-inch innerducts in to a 4-inch conduit. Using this type of system, you may fit four 11/4-inch or six 1-inch innerducts in the conduit.”
When selecting innerduct, you also have to be concerned with its tensile strength and crush resistance. “The thicker the wall material, the larger the tensile rating,” says Stewart. “If you`re gonna pull it more than a long distance, select 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 you can`t pull within the cable,” he explains.
As a result of limited volume of tensile pull that you could exert about the cable, people search for strategies to lessen the coefficient of friction inside the conduit. “You can find products in the marketplace including prelubricated conduit,” says Stewart. “And there`s a good different technology being used for placing cable, known as air-blown fiber (or ABF), where fiber-optic cable is blown into the conduit. We manufacture everything we call the `air-trak` system–a conduit system with chambers–to use in ABF installations.” [Air-blown fiber is available in the usa 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 capacity inside a premises cabling system. However, every contractor knows that for an installation grows, the amount of cables grows to fill each of the space in the conduit. Therefore, selecting the correct trade dimensions are important, since you must leave sufficient clearance between the walls from the conduit along with other cables (see the eia/tia-569 standard). Typically, conduit trade sizes range between 1/2 to 6 inches in diameter. Minimum conduit size appropriate for backbone cables is 4 inches. Sufficient clearance has to be offered to allow pulling the cable without excessive friction or bending.
The NEC conduit-fill tables define the amount (being a percentage) of various kinds of cable you can use in a conduit. “The NEC typically covers power cables,” says Stewart. “With higher-voltage cables, you will need to consider temperature and impedance, which really don`t apply in the matter of data cables in conduit. The true question for data cable is: Could you pull it into the actual size of duct that you`ve selected?”
“The main decision when installing conduit is the actual size of the conduit and clearance through the wall,” says Clawson. For external use, we use 4-inch PVC conduit, and we try to install the maximum amount of conduit inside the trenches since we can for future use.”
Cables are continually included in conduit systems that are often filled to capacity with generations of older cable. When new cables are added, friction and pulling tension can damage existing cables inside the conduit. A good way to offer future changes is always to subdivide larger conduits with innerducts, that are smaller in diameter than conduit, generally nonmetallic, and semiflexible.
“In an existing structure, many installers do not want to pull new cable across the cable already within the conduit,” says Stewart, “simply because they risk damaging the current cable. To optimize a bigger conduit, they`ll install several smaller innerducts inside it. They`ll pull a reduced fiber cable into one of the innerducts, after which have additional ducts to use for future cable placement.”
Innerducts are classified by outside diameter (OD) whereas trade-size conduits use inside diameter (ID). One-inch innerduct is usually used within buildings; however, 11/4-, 11/2-, and two-inch innerducts are around for larger fiber cables. Although innerducts use up space inside a conduit, they give additional protection and suppleness in constantly changing cabling installations.
“Generally, if you`re installing a 4-inch conduit,” says Smith, “you`ll turn out investing in three 1-inch innerducts: one for fiber, one for data, and something spare. What you should do is pull the maximum amount of dexlpky51 you are able to at installation time.”
Typically created from thermoplastic materials, innerduct has a pull string already installed. It can be purchased 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 the innerduct ensure less friction and tension when pulling cable.
“Corrugated innerduct is utilized in plenum and riser products,” says D`Errico. “And, when produced from high-density polyethylene, it is typically employed for short–1000 feet or less–installations.” Smooth wall is commonly used for direct-buried, trenching, plowing, aerial, and directional boring applications. “The Flexible Metal Conduit Pipe would be that the cable jacket is “lifted” away from and possesses a lesser section of exposure to the pipe, decreasing the coefficient of friction. Although the guideline is: the greater the hole, the simpler it`s will be to tug the cable,” he says.
According to Clawson, “We use ribbed innerduct if we`re pulling one innerduct, because it`s quicker 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 much easier to pull smooth innerduct in addition to a smooth surface, and it also doesn`t kink as easily as ribbed innerduct.”
When working with innerduct, it is essential to verify be it a plenum or non-plenum area and to install the innerduct together with the appropriate support. If the innerduct is secured with tie wraps in a plenum area, always employ plenum-rated products.
Innerduct is often offered in just one color–orange for that fiber-optic communications industry. Color is often installation-specific; as an example, one color for data cable, one for telephone, and the like. “There exists a movement afoot to try and use color designations for various applications,” says Stewart. “Orange is generally communications, red would be for electric power, and yellow for gas.”