In outside-plant installations, conduit is usually installed underground to shield cables from damage as well as facilitate cable placement for immediate and future needs. Also you can install Conduit Fittings Wholesale inside buildings to facilitate pulling cable between two points like from the telecommunications closet (TC) to function-area outlets, or from an equipment room into a TC. To protect, isolate, and identify the cables, innerduct–often known as subduct–might be installed inside existing larger-diameter conduit.
Conduit is defined as a rigid or flexible metal or nonmetallic raceway by which cables could be pulled. Furthermore, although conduit could be used to house various kinds of cable, the National Electrical Code (NEC) uses the term “optical fiber raceway” in Article 770 to explain conduit, or raceways, for optical-fiber cable. Several types of conduit are available, such as electrical metallic tubing (EMT), rigid metal conduit, PVC, fiberglass, and flexible conduit. For premises installations, how-ever, metal flexible conduit is just not recommended as a consequence of potential abrasion problems for the cable jacketing.
Metal conduit, which typically can be purchased in 10-foot lengths, is pretty rigid and needs special tooling and accessories to sign up for it. Nonmetallic conduit can be obtained on reels in longer, continuous lengths which do not really need to be joined as much.
“One problem with installing EMT conduit is that it demands a special skill set and training, in addition to lots of practice–or you find yourself making swing sets,” explains Kevin Smith, project manager at MTS Services (Bedford, NH). “Metal conduit can be purchased in 10-foot lengths so you should do any nonstandard bends by hand, and that`s in which 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 being used–for example, riser- and plenum-rated–but all of our products are produced from thermoplastic materials, such as polyvinylide fluoride [pvdf] and polyvinyl chloride [pvc]. The thermoplastic materials are simpler to install than metal.”
You can find 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 normally polyethylene and it`s certainly not rated. Then there`s a riser product, rated by Underwriters Laboratories [UL], which is generally a thermoplastic material like polyethylene or PVC with fire-retardant chemicals included with it. And also the third type of duct is UL plenum-rated, generally a pvdf product, which happens to be fire-retardant and smoke-resistant,” says Jensen.
According to 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, “fairly often incorporating some sort of silicon,” he says. “For premises cabling, Pyramid provides a plenum raceway (tested to UL-910) as well as a riser raceway (UL-1666) for installation in vertical shafts.” Furthermore, the riser item is halogen-free and it is often used for military, shipboard, or tunnel applications, depending on the specifications.
Needless to say contractors install conduit where building codes require it, and also in which the cabling system needs physical protection or protection from unauthorized access.
“We use conduit in riser and backbone systems from the building entrance to the main distribution frame,” says Karl Clawson, senior vice president and partner, Clawson Communications (Greenwood, IN). “So we also set it up for horizontal cabling, specially in university campuses. Inside the living quarters, we install cable in conduit since it affords 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 instance, electricians that have more experience of performing this task. “Generally, the sole time we use Plastic Flexible Conduit occurs when we`re constructing a riser or penetrating a fire wall,” says Smith. “Typically, we might not install conduit from the wiring closet on the workstation outlet. For short distances, up to 100 feet, we will install conduit between buildings according to the existing infrastructure.
Besides the traditional smooth-bore type, innerduct is offered having a ribbed inner wall to lower 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 and the wall from the duct, thus reducing the coefficient of friction and allowing you to pull cable over longer distances,” says Stewart.
Another variation is the multicelled conduit system, that provides outerducts with pre-installed innerducts. Clawson states that, simply because of its cost, his company is not going to use conduit with pre- installed innerduct. “We keep leftover conduit in stock to use on other jobs,” he says. “But pre-installed conduit can be a special application, so overages and underages are type of costly to handle.”
For premises applications, Dura-line (Knoxville, TN) has designed a conduit, generally known as Hex-line, for multiple-duct applications between buildings. “As you pull the ducts off of the reel (two to every single reel), they get into a collector, which Dura-line supplies totally free,” says Ray McLeary, v . p . of sales. “Each duct has a men and women part, which can be snapped together, building a multiple duct system. This saves time, space, and money, but the most important savings is space.” He explains: “Normally, you are able to put three 1-inch innerducts right into a 4-inch conduit. Using this system, it is possible to fit four 11/4-inch or six 1-inch innerducts in the conduit.”
When buying innerduct, you also have to be worried about its tensile strength and crush resistance. “The thicker the wall material, the larger the tensile rating,” says Stewart. “If you`re going to pull it more than a cross country, pick a wall thickness that permits you to pull the duct over that distance. The crush-resistance feature helps to make sure that the innerduct won`t be damaged through the placing process–or perhaps you can`t pull inside the cable,” he explains.
As a result of limited quantity of tensile pull that you can exert in the cable, people try to find approaches to lessen the coefficient of friction inside of the conduit. “There are actually products available on the market like prelubricated conduit,” says Stewart. “And there`s a different technology used for placing cable, generally known as air-blown fiber (or ABF), where fiber-optic cable is blown to the conduit. We manufacture whatever we call the `air-trak` system–a conduit system with chambers–to use in ABF installations.” [Air-blown fiber is available in the United States from Sumitomo Electric Lightwave Corp. (Research Triangle Park, NC).]
Conduit and innerduct have something in common: They facilitate pulling or replacing a cable for more capacity inside a premises cabling system. However, every contractor knows that being an installation grows, the quantity of cables grows to fill every one of the space inside the conduit. Therefore, picking out the correct trade size is important, since you must leave sufficient clearance between your walls of your conduit as well as other cables (begin to see the eia/tia-569 standard). Typically, conduit trade sizes vary from 1/2 to 6 inches in diameter. Minimum conduit size suggested for backbone cables is 4 inches. Sufficient clearance must be accessible to allow pulling the cable without excessive friction or bending.
The NEC conduit-fill tables define the quantity (being a percentage) of different kinds of cable you can use in a conduit. “The NEC typically covers power cables,” says Stewart. “With good-voltage cables, you will need to consider temperature and impedance, which really don`t apply when it comes to data cables in conduit. The true question for data cable is: Could you pull it into the dimensions of duct that you`ve selected?”
“The most crucial decision when installing conduit is the actual size of the conduit and clearance from the wall,” says Clawson. For external use, we use 4-inch PVC conduit, and that we try to install just as much conduit within the trenches as we can for future use.”
Cables are continually added to conduit systems which can be often filled to capacity with generations of older cable. When new cables are added, friction and pulling tension can harm existing cables within the conduit. One method to provide for future changes is usually to subdivide larger conduits with innerducts, which are smaller in diameter than conduit, generally nonmetallic, and semiflexible.
“Inside an existing structure, many installers will not wish to pull new cable across the cable already inside the conduit,” says Stewart, “since they risk damaging the present cable. To optimize a greater conduit, they`ll install several smaller innerducts inside it. They`ll pull a reduced fiber cable into one of many 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 generally used within buildings; however, 11/4-, 11/2-, and 2-inch innerducts are available for larger fiber cables. Although innerducts take up space within a conduit, they give additional protection and flexibility 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 one spare. What you should do is pull all the dexlpky51 you are able to at installation time.”
Typically constructed from thermoplastic materials, innerduct includes a pull string already installed. It can be found in ribbed-, corrugated-, and smooth-wall styles. Some types have prelubricated inside walls. These special coatings and also the physical properties in 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 constructed from high-density polyethylene, it is typically used for short–1000 feet or less–installations.” Smooth wall can be used for direct-buried, trenching, plowing, aerial, and directional boring applications. “The Metal Flexible Conduit is the fact that cable jacket is “lifted” away from and possesses a smaller part of exposure to the pipe, decreasing the coefficient of friction. Although the general guideline is: the greater the hole, the better it`s will be to drag the cable,” he says.
As outlined by 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 can be quicker to pull smooth innerduct along with an easy surface, and it doesn`t kink as easily as ribbed innerduct.”
When using innerduct, you should verify be it a plenum or non-plenum area and also to install the innerduct with the appropriate support. In the event the innerduct is secured with tie wraps inside a plenum area, always use plenum-rated products.
Innerduct is usually offered in a color–orange for your fiber-optic communications industry. Color can sometimes be installation-specific; for example, one color for data cable, one for telephone, and the like. “You will discover a movement afoot in order to use color designations for various applications,” says Stewart. “Orange is normally communications, red can be for electricity, and yellow for gas.”