In outside-plant installations, conduit is typically installed underground to safeguard cables from damage as well as 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 including from your telecommunications closet (TC) to operate-area outlets, or from an equipment room to some TC. To protect, isolate, and identify the cables, innerduct–also referred to as subduct–can be installed inside existing larger-diameter conduit.
Conduit is defined as a rigid or flexible metal or nonmetallic raceway through which cables might be pulled. In addition, although conduit could be used to house many types of cable, the National Electrical Code (NEC) uses the term “optical fiber raceway” in Article 770 to clarify conduit, or raceways, for optical-fiber cable. Various kinds conduit are offered, for example electrical metallic tubing (EMT), rigid metal conduit, PVC, fiberglass, and flexible conduit. For premises installations, how-ever, metal flexible conduit is not recommended due to potential abrasion injury to the cable jacketing.
Metal conduit, which typically comes in 10-foot lengths, is fairly rigid and requires special tooling and accessories to sign up with it. Nonmetallic conduit can be obtained on reels in longer, continuous lengths which do not need to be joined as frequently.
“The only problem with installing EMT conduit is that it takes 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 have to do any nonstandard bends by hand, and that`s where the technician`s special skill is necessary.”
Arnco Corp. (Elyria, OH) sells innerduct to the cable-TV, telecommunications, and electric utility markets, says Tom Stewart, electrical products sales manager. “In a building, several kinds of duct are used–for instance, riser- and plenum-rated–but all of our products are manufactured from thermoplastic materials, like polyvinylide fluoride [pvdf] and polyvinyl chloride [pvc]. The thermoplastic materials are easier to install than metal.”
You will find three differing types (or ratings) of innerduct: outdoor, riser-rated, and plenum-rated. Robert Jensen, engineering manager at Endot Industries Inc. (Rockaway, NJ), explains: “Outdoor is usually polyethylene and it`s not necessarily rated. Then there`s a riser product, rated by Underwriters Laboratories [UL], which happens to be generally a thermoplastic material like polyethylene or PVC with fire-retardant chemicals added to it. And the third sort of duct is UL plenum-rated, generally a pvdf product, which can be fire-retardant and smoke-resistant,” says Jensen.
In accordance with Mike D`Errico, regional director of sales at Pyramid Industries (Erie, PA), most products that conduit and innerduct manufacturers make is made for outside plant. Some manufacturers offer prelubricated innerduct and conduit, “frequently incorporating some sort 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.” Moreover, the riser product is halogen-free and is often useful for military, shipboard, or tunnel applications, based on the specifications.
Obviously contractors install conduit where building codes require it, but additionally the location where the cabling system needs physical protection or protection from unauthorized access.
“We use conduit in riser and backbone systems in the building entrance on the main distribution frame,” says Karl Clawson, senior v . p . and partner, Clawson Communications (Greenwood, IN). “And we also install it for horizontal cabling, especially in university campuses. From the living quarters, we install cable in conduit since 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; as an example, electricians who may have more expertise in performing this task. “Generally, the only time we use Flexible Plastic Conduit for Cables happens when we`re building a riser or penetrating a fire wall,” says Smith. “Typically, we may not install conduit through the wiring closet to the workstation outlet. In short distances, just as much as 100 feet, we may install conduit between buildings according to the existing infrastructure.
In addition to the traditional smooth-bore type, innerduct is available with a ribbed inner wall to minimize friction between the cable sheath and also the innerduct wall. “A wave-rib on the inside of the duct reduces surface contact between your cable as well as the wall in the duct, thus reducing the coefficient of friction and enabling you to pull cable over longer distances,” says Stewart.
Another variation is definitely the multicelled conduit system, that offers outerducts with pre-installed innerducts. Clawson states that, simply because of its cost, his company does not use conduit with pre- installed innerduct. “We keep leftover conduit available to utilize on other jobs,” he says. “But pre-installed conduit is actually a special application, so overages and underages are form of costly to manage.”
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 each reel), they go into a collector, which Dura-line supplies free of charge,” says Ray McLeary, v . p . of sales. “Each duct carries a male and female part, which can be snapped together, making a multiple duct system. This saves time, space, and funds, but the main savings is space.” He explains: “Normally, it is possible to put three 1-inch innerducts into a 4-inch conduit. Using this type of system, you may fit four 11/4-inch or six 1-inch innerducts to the conduit.”
When purchasing innerduct, you also need 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 across a cross country, decide on 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 throughout the placing process–or perhaps you can`t pull within the cable,” he explains.
Because of the limited volume of tensile pull that you can exert around the cable, people seek out methods to minimize the coefficient of friction inside of the conduit. “You will find products in the marketplace for example prelubricated conduit,” says Stewart. “And there`s even a different technology used for placing cable, referred to as air-blown fiber (or ABF), in which the fiber-optic cable is blown into the conduit. We manufacture what we should call the `air-trak` system–a conduit system with chambers–for usage in ABF installations.” [Air-blown fiber is available 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 more capacity within a premises cabling system. However, every contractor recognizes that being an installation grows, the number of cables grows to fill all of the space within the conduit. Therefore, picking out the correct trade dimension is important, as you must leave sufficient clearance in between the walls in the conduit and other cables (start to see the eia/tia-569 standard). Typically, conduit trade sizes vary from 1/2 to 6 inches in diameter. Minimum conduit size appropriate for backbone cables is 4 inches. Sufficient clearance needs to be available 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 the conduit. “The NEC typically covers power cables,” says Stewart. “With higher-voltage cables, you need to consider temperature and impedance, which really don`t apply in the matter of data cables in conduit. The genuine question for data cable is: Can you pull it into the size of duct that you`ve selected?”
“The most crucial 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, and we make an effort to install as much conduit in the trenches when we can for future use.”
Cables are continually included in conduit systems which can be often filled to capacity with generations of older cable. When new cables are added, friction and pulling tension may damage existing cables within the conduit. A good way to provide for future changes would be to subdivide larger conduits with innerducts, that are smaller in diameter than conduit, generally nonmetallic, and semiflexible.
“In a existing structure, many installers tend not to wish to pull new cable across the cable already inside the conduit,” says Stewart, “since they risk damaging existing cable. To optimize a more substantial conduit, they`ll install several smaller innerducts within it. They`ll pull a reduced fiber cable into one of several 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 often used within buildings; however, 11/4-, 11/2-, and two-inch innerducts are for sale to larger fiber cables. Although innerducts consume space inside a conduit, they give additional protection and adaptability in constantly changing cabling installations.
“Generally, if you`re installing a 4-inch conduit,” says Smith, “you`ll find yourself putting in three 1-inch innerducts: one for fiber, one for data, then one spare. What you want to do is pull the maximum amount of dexlpky51 you are able to at installation time.”
Typically produced from thermoplastic materials, innerduct comes with 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 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 used for short–1000 feet or less–installations.” Smooth wall can be used for direct-buried, trenching, plowing, aerial, and directional boring applications. “The Flexible Metal Conduit Pipe would be that the cable jacket is “lifted” from and has a lesser part of exposure to the pipe, decreasing the coefficient of friction. Nevertheless 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 simpler to handle. If we`re pulling by way of a directional boring machine and it`s a multiple pull, we use smooth innerduct. It really is easier to pull smooth innerduct on top of an easy surface, plus it doesn`t kink as easily as ribbed innerduct.”
When working with innerduct, you should verify be it a plenum or non-plenum area and also to install the innerduct with the appropriate support. In case the innerduct is secured with tie wraps in the plenum area, only use plenum-rated products.
Innerduct is generally offered in one color–orange for the fiber-optic communications industry. Color can occasionally be installation-specific; by way of example, one color for data cable, one for telephone, etc. “There exists a movement afoot in order to use color designations for various types of applications,” says Stewart. “Orange is normally communications, red could be for electricity, and yellow for gas.”