In outside-plant installations, conduit is usually installed underground to guard cables from damage as well as facilitate cable placement for fast and future needs. You can even install Conduit Fittings Wholesale inside buildings to facilitate pulling cable between two points including in the telecommunications closet (TC) to be effective-area outlets, or from an equipment room to some TC. To protect, isolate, and identify the cables, innerduct–also referred to as subduct–may be installed inside existing larger-diameter conduit.
Conduit is described as a rigid or flexible metal or nonmetallic raceway whereby cables may be pulled. Furthermore, although conduit could be used to house various types of cable, the National Electrical Code (NEC) uses the word “optical fiber raceway” in Article 770 to illustrate conduit, or raceways, for optical-fiber cable. Several kinds of conduit are available, like electrical metallic tubing (EMT), rigid metal conduit, PVC, fiberglass, and versatile conduit. For premises installations, how-ever, metal flexible conduit will not be recommended as a consequence of potential abrasion damage to the cable jacketing.
Metal conduit, which typically will come in 10-foot lengths, is rather rigid and requires special tooling and accessories to join it. Nonmetallic conduit is offered on reels in longer, continuous lengths which do not must be joined as much.
“One problem with installing EMT conduit is that it demands a special skill set and training, as well as plenty 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 essential.”
Arnco Corp. (Elyria, OH) sells innerduct on 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 our products are produced from thermoplastic materials, such as polyvinylide fluoride [pvdf] and polyvinyl chloride [pvc]. The thermoplastic materials are easier 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 certainly not rated. Then there`s a riser product, rated by Underwriters Laboratories [UL], that is generally a thermoplastic material including polyethylene or PVC with fire-retardant chemicals included in it. As well as the third form of duct is UL plenum-rated, generally a pvdf product, that is fire-retardant and smoke-resistant,” says Jensen.
According to Mike D`Errico, regional director of sales at Pyramid Industries (Erie, PA), most products that conduit and innerduct manufacturers make is perfect for outside plant. Some manufacturers offer prelubricated innerduct and conduit, “often incorporating some sort of silicon,” he says. “For premises cabling, Pyramid supplies a plenum raceway (tested to UL-910) as well as a riser raceway (UL-1666) for installation in vertical shafts.” Furthermore, the riser product is halogen-free which is often used for military, shipboard, or tunnel applications, based on the specifications.
Needless to say contractors install conduit where building codes require it, but additionally the location where the cabling system needs physical protection or defense against unauthorized access.
“We use conduit in riser and backbone systems from the building entrance towards the main distribution frame,” says Karl Clawson, senior v . p . and partner, Clawson Communications (Greenwood, IN). “So we also do the installation for horizontal cabling, particularly in university campuses. Within the living quarters, we install cable in conduit as it gives the cable extra protection, and hopefully, keeps it all out of students` reach,” he says.
Some cabling contractors choose to have other trades install conduit; by way of example, electricians who have more experience of performing this task. “Generally, the only time we use Plastic Flexible Conduit is when we`re constructing a riser or penetrating a fire wall,” says Smith. “Typically, we will not install conduit in the wiring closet towards the workstation outlet. For brief distances, just as much as 100 feet, we will install conduit between buildings based on the existing infrastructure.
Along with the traditional smooth-bore type, innerduct is accessible by using 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 in between the cable as well as the wall in the duct, thus reducing the coefficient of friction and helping you to pull cable over longer distances,” says Stewart.
Another variation may be the multicelled conduit system, that offers outerducts with pre-installed innerducts. Clawson says that, simply because of its cost, his company does not 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 cope with.”
For premises applications, Dura-line (Knoxville, TN) has designed a conduit, generally known as Hex-line, for multiple-duct applications between buildings. “While 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, vice president of sales. “Each duct has a female and male part, which can be snapped together, setting up a multiple duct system. This saves time, space, and funds, but the most important savings is space.” He explains: “Normally, you may put three 1-inch innerducts in a 4-inch conduit. With this particular system, you can fit four 11/4-inch or six 1-inch innerducts in to the conduit.”
When choosing innerduct, you also need to be concerned with its tensile strength and crush resistance. “The thicker the wall material, the greater the tensile rating,” says Stewart. “If you`re going to pull it spanning a cross country, select a wall thickness that lets you pull the duct over that distance. The crush-resistance feature helps to ensure the innerduct won`t be damaged throughout the placing process–or else you can`t pull inside the cable,” he explains.
Due to the limited volume of tensile pull that one could exert in the cable, people try to find strategies to lessen the coefficient of friction in the conduit. “There are actually products available on the market including prelubricated conduit,” says Stewart. “And there`s a good different technology being utilized for placing cable, referred to as air-blown fiber (or ABF), the location where the fiber-optic cable is blown into the conduit. We manufacture whatever we call the `air-trak` system–a conduit system with chambers–to be used in ABF installations.” [Air-blown fiber is offered in the usa from Sumitomo Electric Lightwave Corp. (Research Triangle Park, NC).]
Conduit and innerduct have a very important factor in common: They facilitate pulling or replacing a cable for additional capacity in the premises cabling system. However, every contractor knows that for an installation grows, the number of cables grows to fill each of the space inside the conduit. Therefore, selecting the correct trade size is important, because you must leave sufficient clearance between your walls from the conduit along with other cables (view the eia/tia-569 standard). Typically, conduit trade sizes range from 1/2 to 6 inches in diameter. Minimum conduit size suitable for backbone cables is 4 inches. Sufficient clearance must be open to allow pulling the cable without excessive friction or bending.
The NEC conduit-fill tables define the exact amount (as being a percentage) of various kinds of cable you may use inside a 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 actual question for data cable is: Are you able to pull it into the size of duct that you`ve selected?”
“The most crucial decision when installing conduit is the dimensions of the conduit and clearance through the wall,” says Clawson. For external use, we use 4-inch PVC conduit, and we attempt to install the maximum amount of conduit within the trenches as we can for future use.”
Cables are continually added to conduit systems that happen to be often filled to capacity with generations of older cable. When new cables are added, friction and pulling tension can damage existing cables within the conduit. One method to offer future changes is to subdivide larger conduits with innerducts, that happen to be smaller in diameter than conduit, generally nonmetallic, and semiflexible.
“Inside an existing structure, many installers tend not to want to pull new cable on the cable already within the conduit,” says Stewart, “since they risk damaging the present cable. To optimize a greater conduit, they`ll install several smaller innerducts within it. They`ll pull a reduced fiber cable into one of the innerducts, and then have additional ducts to be used 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 2-inch innerducts are accessible for larger fiber cables. Although innerducts consume space in just a conduit, they supply additional protection and adaptability in constantly changing cabling installations.
“Generally, if you`re installing a 4-inch conduit,” says Smith, “you`ll wind up setting up three 1-inch innerducts: one for fiber, one for data, and something spare. What you should do is pull the maximum amount of dexlpky51 it is possible to at installation time.”
Typically constructed from thermoplastic materials, innerduct includes a pull string already installed. It comes in ribbed-, corrugated-, and smooth-wall styles. Some types have prelubricated inside walls. These special coatings along with 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 produced from high-density polyethylene, it is typically used for short–1000 feet or less–installations.” Smooth wall is used for direct-buried, trenching, plowing, aerial, and directional boring applications. “The Flexible Metal Conduit Pipe is the cable jacket is “lifted” clear of and contains a reduced region of exposure to the pipe, decreasing the coefficient of friction. Nevertheless the general guideline is: the larger the hole, the simpler 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 using a directional boring machine and it`s a multiple pull, then we use smooth innerduct. It can be simpler to pull smooth innerduct in addition to an easy surface, and yes it doesn`t kink as easily as ribbed innerduct.”
When utilizing innerduct, it is very important verify whether it is a plenum or non-plenum area and to install the innerduct with all the appropriate support. When the innerduct is secured with tie wraps inside a plenum area, always employ plenum-rated products.
Innerduct is generally offered in one color–orange for that fiber-optic communications industry. Color can sometimes be installation-specific; by way of example, one color for data cable, one for telephone, and so forth. “You will discover a movement afoot to try and use color designations for various applications,” says Stewart. “Orange is generally communications, red can be for electrical power, and yellow for gas.”