In outside-plant installations, conduit is usually installed underground to protect cables from damage as well as facilitate cable placement for immediate and future needs. You can even install Conduit Fittings Wholesale inside buildings to facilitate pulling cable between two points including from the telecommunications closet (TC) to operate-area outlets, or from an equipment room into a TC. To shield, isolate, and identify the cables, innerduct–often known as subduct–can be installed inside existing larger-diameter conduit.
Conduit is described as a rigid or flexible metal or nonmetallic raceway by which cables can be pulled. Furthermore, although conduit could be used to house various kinds of cable, the National Electrical Code (NEC) uses the word “optical fiber raceway” in Article 770 to clarify conduit, or raceways, for optical-fiber cable. Various kinds conduit are available, such as electrical metallic tubing (EMT), rigid metal conduit, PVC, fiberglass, and versatile conduit. For premises installations, how-ever, metal flexible conduit is not recommended as a result of potential abrasion harm to the cable jacketing.
Metal conduit, which typically will come in 10-foot lengths, is pretty rigid and requires special tooling and accessories to join it. Nonmetallic conduit is available on reels in longer, continuous lengths that do not really need to be joined as frequently.
“The only problem with installing EMT conduit is that it needs a special skill set and training, as well as lots of practice–or you end up making swing sets,” explains Kevin Smith, project manager at MTS Services (Bedford, NH). “Metal conduit is available in 10-foot lengths so you have to do any nonstandard bends yourself, and that`s where technician`s special skill is essential.”
Arnco Corp. (Elyria, OH) sells innerduct for the cable-TV, telecommunications, and electric utility markets, says Tom Stewart, electrical products sales manager. “Within a building, various kinds of duct are used–for instance, riser- and plenum-rated–but all of our products are manufactured from thermoplastic materials, including polyvinylide fluoride [pvdf] and polyvinyl chloride [pvc]. The thermoplastic materials are easier to install than metal.”
You will find three different kinds (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 not really rated. Then there`s a riser product, rated by Underwriters Laboratories [UL], which is generally a thermoplastic material such as polyethylene or PVC with fire-retardant chemicals put into it. And the third form of duct is UL plenum-rated, generally a pvdf product, which 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 perfect for outside plant. Some manufacturers offer prelubricated innerduct and conduit, “very often incorporating some form 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.” Additionally, the riser item is halogen-free and is often used for military, shipboard, or tunnel applications, based upon the specifications.
Needless to say contractors install conduit where building codes require it, but in addition where the cabling system needs physical protection or defense against unauthorized access.
“We use conduit in riser and backbone systems in the building entrance for 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, particularly in university campuses. From 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 choose to have other trades install conduit; by way of example, electricians who definitely have more experience of performing this. “Generally, the only real time we use Plastic Flexible Conduit occurs when we`re creating a riser or penetrating a fire wall,” says Smith. “Typically, we might not install conduit through the wiring closet to the workstation outlet. In short distances, as much as 100 feet, we will install conduit between buildings according to the existing infrastructure.
In addition to the traditional smooth-bore type, innerduct is available using a ribbed inner wall to minimize friction between the cable sheath as well as the innerduct wall. “A wave-rib within the duct reduces surface contact in between the cable as well as the wall of the duct, thus lowering 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, due to the cost, his company does not use conduit with pre- installed innerduct. “We keep leftover conduit in stock to utilize on other jobs,” he says. “But pre-installed conduit can be a special application, so overages and underages are type of costly to deal with.”
For premises applications, Dura-line (Knoxville, TN) has designed a conduit, called Hex-line, for multiple-duct applications between buildings. “While you pull the ducts off the reel (two to each and every reel), they get into a collector, which Dura-line supplies free of charge,” says Ray McLeary, v . p . of sales. “Each duct has a male and female part, which can be snapped together, setting up a multiple duct system. This saves time, space, and money, but the main savings is space.” He explains: “Normally, you are able to put three 1-inch innerducts in to a 4-inch conduit. With this particular system, it is possible to fit four 11/4-inch or six 1-inch innerducts to the conduit.”
When purchasing innerduct, you also have to be concerned with its tensile strength and crush resistance. “The thicker the wall material, the better the tensile rating,” says Stewart. “If you`re going to pull it across a great distance, pick a wall thickness that lets you pull the duct over that distance. The crush-resistance feature helps to make certain that the innerduct won`t be damaged through the placing process–or else you can`t pull within the cable,” he explains.
Due to the limited amount of tensile pull that you could exert on the cable, people search for methods to lessen the coefficient of friction in the conduit. “There are actually products available on the market like prelubricated conduit,” says Stewart. “And there`s a good different technology used for placing cable, called air-blown fiber (or ABF), in which the fiber-optic cable is blown in 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 offered 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 in a premises cabling system. However, every contractor is aware that as being an installation grows, the quantity of cables grows to fill every one of the space within the conduit. Therefore, picking out the correct trade dimensions are important, simply because you must leave sufficient clearance in between the walls in the conduit and also other cables (begin to see the eia/tia-569 standard). Typically, conduit trade sizes cover anything from 1/2 to 6 inches in diameter. Minimum conduit size appropriate for backbone cables is 4 inches. Sufficient clearance should be accessible to allow pulling the cable without excessive friction or bending.
The NEC conduit-fill tables define the total amount (as being a percentage) of different kinds of cable you can use inside a conduit. “The NEC typically covers power cables,” says Stewart. “Rich in-voltage cables, you must consider temperature and impedance, which really don`t apply in the matter of data cables in conduit. The genuine question for data cable is: Are you able to pull it into the actual size of duct that you`ve selected?”
“The most important decision when installing conduit is the size of the conduit and clearance through the wall,” says Clawson. For external use, we use 4-inch PVC conduit, and we attempt to install as much conduit from the trenches while 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 great way to offer future changes is to subdivide larger conduits with innerducts, which can be smaller in diameter than conduit, generally nonmetallic, and semiflexible.
“Within an existing structure, many installers tend not to would like to pull new cable across the cable already from the conduit,” says Stewart, “since they risk damaging the present cable. To optimize a larger conduit, they`ll install several smaller innerducts within it. They`ll pull a smaller fiber cable into one of many innerducts, 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 normally used within buildings; however, 11/4-, 11/2-, and 2-inch innerducts are accessible for larger fiber cables. Although innerducts occupy space in just a conduit, they supply additional protection and suppleness in constantly changing cabling installations.
“Generally, if you`re installing a 4-inch conduit,” says Smith, “you`ll end up 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 constructed from thermoplastic materials, innerduct includes 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 along with the physical properties of your inner wall from the 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 employed for short–1000 feet or less–installations.” Smooth wall is utilized for direct-buried, trenching, plowing, aerial, and directional boring applications. “The Flexible Metal Conduit Pipe is the cable jacket is “lifted” from and possesses a smaller area of exposure to the pipe, lowering the coefficient of friction. However the general guideline is: the greater the hole, the better it`s will be to pull the cable,” he says.
In accordance with Clawson, “We use ribbed innerduct if we`re pulling one innerduct, because it`s quicker to handle. If we`re pulling via a directional boring machine and it`s a multiple pull, we use smooth innerduct. It is actually easier to pull smooth innerduct on top of an even surface, plus it doesn`t kink as easily as ribbed innerduct.”
When using innerduct, it is essential to verify whether it be a plenum or non-plenum area and also to install the innerduct together with the appropriate support. If the innerduct is secured with tie wraps in the plenum area, only use plenum-rated products.
Innerduct is generally offered in a color–orange to the fiber-optic communications industry. Color can often be installation-specific; for example, one color for data cable, one for telephone, and so on. “You will discover a movement afoot to attempt to use color designations for various applications,” says Stewart. “Orange is generally communications, red will be for electrical power, and yellow for gas.”