In outside-plant installations, conduit is normally installed underground to shield cables from damage as well as facilitate cable placement for immediate and future needs. You can also install Conduit Fittings Wholesale inside buildings to facilitate pulling cable between two points like in the telecommunications closet (TC) to function-area outlets, or from an equipment room to some TC. To protect, isolate, and identify the cables, innerduct–often known as subduct–might be installed inside existing larger-diameter conduit.
Conduit is identified as a rigid or flexible metal or nonmetallic raceway in which cables can be pulled. Moreover, 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 explain conduit, or raceways, for optical-fiber cable. Several types of conduit can be found, like electrical metallic tubing (EMT), rigid metal conduit, PVC, fiberglass, and versatile conduit. For premises installations, how-ever, metal flexible conduit is just not recommended as a consequence of potential abrasion injury to the cable jacketing.
Metal conduit, which typically will come in 10-foot lengths, is rather rigid and needs special tooling and accessories to sign up with it. Nonmetallic conduit is available on reels in longer, continuous lengths which do not have to be joined as often.
“A possible problem with installing EMT conduit is that it needs a special skill set and training, as well as a great deal 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 need to do any nonstandard bends manually, and that`s in which the technician`s special skill is important.”
Arnco Corp. (Elyria, OH) sells innerduct towards the cable-TV, telecommunications, and electric utility markets, says Tom Stewart, electrical products sales manager. “In a building, several kinds of duct are used–by way of example, riser- and plenum-rated–but all of our products are produced from thermoplastic materials, like polyvinylide fluoride [pvdf] and polyvinyl chloride [pvc]. The thermoplastic materials are easier to install than metal.”
You will 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 not really rated. Then there`s a riser product, rated by Underwriters Laboratories [UL], which happens to be generally a thermoplastic material including polyethylene or PVC with fire-retardant chemicals included in it. And the third form of duct is UL plenum-rated, generally a pvdf product, which can be fire-retardant and smoke-resistant,” says Jensen.
Based on 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, “often incorporating some form of silicon,” he says. “For premises cabling, Pyramid offers a plenum raceway (tested to UL-910) and a riser raceway (UL-1666) for installation in vertical shafts.” Furthermore, the riser product is halogen-free and is also often useful for military, shipboard, or tunnel applications, depending upon the specifications.
Needless to say contractors install conduit where building codes require it, but in addition in which the cabling system needs physical protection or defense against unauthorized access.
“We use conduit in riser and backbone systems from your building entrance on the main distribution frame,” says Karl Clawson, senior vice president and partner, Clawson Communications (Greenwood, IN). “Therefore we also set it up for horizontal cabling, specially in university campuses. From the living quarters, we install cable in conduit as it allows 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; for instance, electricians who definitely have more experience in performing this task. “Generally, the only time we use Plastic Flexible Conduit happens when we`re building a riser or penetrating a fire wall,” says Smith. “Typically, we will not install conduit through the wiring closet towards the workstation outlet. In short distances, as much as 100 feet, we will install conduit between buildings based on the existing infrastructure.
In addition to the traditional smooth-bore type, innerduct is offered with a ribbed inner wall to minimize friction involving the cable sheath along with the innerduct wall. “A wave-rib on the inside of the duct reduces surface contact between the cable and the wall of your duct, thus reducing the coefficient of friction and allowing you to pull cable over longer distances,” says Stewart.
Another variation may be the multicelled conduit system, which provides outerducts with pre-installed innerducts. Clawson states that, due to the cost, his company will not use conduit with pre- installed innerduct. “We keep leftover conduit in stock to utilize on other jobs,” he says. “But pre-installed conduit is really a special application, so overages and underages are type of costly to manage.”
For premises applications, Dura-line (Knoxville, TN) has created a conduit, called Hex-line, for multiple-duct applications between buildings. “When you pull the ducts from the reel (two to every single reel), they get into a collector, which Dura-line supplies cost-free,” says Ray McLeary, v . p . of sales. “Each duct carries a female and male part, which can be snapped together, setting up a multiple duct system. This saves time, space, and cash, but the main savings is space.” He explains: “Normally, you may put three 1-inch innerducts in to a 4-inch conduit. With this system, you can fit four 11/4-inch or six 1-inch innerducts to the conduit.”
When purchasing innerduct, you also need to be concerned with its tensile strength and crush resistance. “The thicker the wall material, the higher the tensile rating,” says Stewart. “If you`re going to pull it over a cross country, 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 perhaps you can`t pull from the cable,” he explains.
Because of the limited volume of tensile pull that you could exert on the cable, people search for ways to minimize the coefficient of friction within the conduit. “There are actually products available on the market such as prelubricated conduit,” says Stewart. “And there`s also a different technology being used for placing cable, known as air-blown fiber (or ABF), where the fiber-optic cable is blown into the conduit. We manufacture what we call the `air-trak` system–a conduit system with chambers–for usage in ABF installations.” [Air-blown fiber can be obtained in the United States from Sumitomo Electric Lightwave Corp. (Research Triangle Park, NC).]
Conduit and innerduct have one thing in common: They facilitate pulling or replacing a cable for more capacity in a premises cabling system. However, every contractor knows that as an installation grows, the quantity of cables grows to fill every one of the space from the conduit. Therefore, choosing the correct trade size is important, simply because you must leave sufficient clearance involving the walls of the conduit and other cables (view the eia/tia-569 standard). Typically, conduit trade sizes range between 1/2 to 6 inches in diameter. Minimum conduit size recommended for backbone cables is 4 inches. Sufficient clearance should be open to allow pulling the cable without excessive friction or bending.
The NEC conduit-fill tables define the amount (as being a percentage) of different types of cable you can utilize in the conduit. “The NEC typically covers power cables,” says Stewart. “With high-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: Are you able to pull it into the dimensions of duct that you`ve selected?”
“The most significant decision when installing conduit is the actual size of the conduit and clearance in the wall,” says Clawson. For external use, we use 4-inch PVC conduit, therefore we try to install all the conduit within 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 can damage existing cables in the conduit. One method to offer future changes is always to subdivide larger conduits with innerducts, which are smaller in diameter than conduit, generally nonmetallic, and semiflexible.
“In an existing structure, many installers tend not to wish to pull new cable across the cable already from the conduit,” says Stewart, “because they risk damaging the existing cable. To optimize a more substantial conduit, they`ll install several smaller innerducts within it. They`ll pull a smaller fiber cable into among the innerducts, after which 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 turn out putting in three 1-inch innerducts: one for fiber, one for data, and another spare. What for you to do is pull the maximum amount of dexlpky51 you can at installation time.”
Typically produced 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 in the 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 constructed 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 Flexible Metal Conduit Pipe is the fact that cable jacket is “lifted” clear of and possesses a lesser section of experience of the pipe, lowering the coefficient of friction. Nevertheless the rule of thumb is: the greater the hole, the simpler it`s going to be to drag the cable,” he says.
In accordance with Clawson, “We use ribbed innerduct if we`re pulling one innerduct, because it`s easier to handle. If we`re pulling using a directional boring machine and it`s a multiple pull, we use smooth innerduct. It can be much easier to pull smooth innerduct in addition to a smooth surface, and it doesn`t kink as easily as ribbed innerduct.”
When utilizing innerduct, it is very important verify whether it be a plenum or non-plenum area as well as install the innerduct using the appropriate support. In the event the innerduct is secured with tie wraps in a plenum area, only take plenum-rated products.
Innerduct is normally offered in a color–orange for that fiber-optic communications industry. Color can occasionally be installation-specific; by way of example, one color for data cable, one for telephone, and so on. “There exists a movement afoot to attempt to use color designations for various applications,” says Stewart. “Orange is usually communications, red would be for electrical power, and yellow for gas.”