In outside-plant installations, conduit is typically installed underground to protect cables from damage and also to facilitate cable placement for fast and future needs. You can also 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 to some TC. To guard, isolate, and identify the cables, innerduct–also referred to as subduct–may be installed inside existing larger-diameter conduit.
Conduit is identified as a rigid or flexible metal or nonmetallic raceway by which cables could be pulled. Moreover, although conduit can be used to house various kinds of cable, the National Electrical Code (NEC) uses the word “optical fiber raceway” in Article 770 to explain conduit, or raceways, for optical-fiber cable. Several types of conduit are available, including 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 result of potential abrasion injury to the cable jacketing.
Metal conduit, which typically is available in 10-foot lengths, is fairly rigid and needs special tooling and accessories to participate it. Nonmetallic conduit is available on reels in longer, continuous lengths that do not have to be joined as often.
“The only problem with installing EMT conduit is it needs a special skill set and training, as well as a great deal 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 must do any nonstandard bends yourself, and that`s in which the technician`s special skill is essential.”
Arnco Corp. (Elyria, OH) sells innerduct towards the cable-TV, telecommunications, and electric utility markets, says Tom Stewart, electrical products sales manager. “Within a building, various kinds duct are being 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 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 often polyethylene and it`s definitely not rated. Then there`s a riser product, rated by Underwriters Laboratories [UL], which 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, 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 which conduit and innerduct manufacturers make is for outside plant. Some manufacturers offer prelubricated innerduct and conduit, “fairly often incorporating some type of silicon,” he says. “For premises cabling, Pyramid offers a plenum raceway (tested to UL-910) plus a riser raceway (UL-1666) for installation in vertical shafts.” Additionally, the riser product is halogen-free and it is often employed for military, shipboard, or tunnel applications, based upon the specifications.
Of course contractors install conduit where building codes require it, but also where the cabling system needs physical protection or defense against unauthorized access.
“We use conduit in riser and backbone systems from the building entrance on the main distribution frame,” says Karl Clawson, senior v . p . and partner, Clawson Communications (Greenwood, IN). “And that we also install it for horizontal cabling, especially in university campuses. Inside the living quarters, we install cable in conduit because it gives the cable extra protection, and hopefully, keeps it all out of students` reach,” he says.
Some cabling contractors want to have other trades install conduit; as an example, electricians that have more expertise in performing this task. “Generally, really 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 through the wiring closet for the workstation outlet. In short distances, up to 100 feet, we may install conduit between buildings based on the existing infrastructure.
Along with the traditional smooth-bore type, innerduct is offered having a ribbed inner wall to lower friction between the cable sheath as well as the innerduct wall. “A wave-rib within the duct reduces surface contact between your cable along with 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 says that, because of its cost, his company does not use conduit with pre- installed innerduct. “We keep leftover conduit in store to make use of on other jobs,” he says. “But pre-installed conduit is actually a special application, so overages and underages are kind of costly to cope with.”
For premises applications, Dura-line (Knoxville, TN) has created a conduit, generally known as Hex-line, for multiple-duct applications between buildings. “As you pull the ducts off of the reel (two to each and every reel), they go deep into a collector, which Dura-line supplies totally free,” says Ray McLeary, vice president of sales. “Each duct has a male and female part, which are snapped together, building a multiple duct system. This saves time, space, and money, but the most important savings is space.” He explains: “Normally, you can put three 1-inch innerducts in a 4-inch conduit. With this system, you may fit four 11/4-inch or six 1-inch innerducts in to the conduit.”
When buying 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 likely to pull it more than a great distance, pick a wall thickness that allows you to pull the duct over that distance. The crush-resistance feature helps to ensure the innerduct won`t be damaged throughout the placing process–or perhaps you can`t pull within the cable,” he explains.
Due to the limited quantity of tensile pull you could exert about the cable, people search for methods to reduce the coefficient of friction in the conduit. “You can find products on the market like prelubricated conduit,” says Stewart. “And there`s also a different technology used for placing cable, referred to as air-blown fiber (or ABF), where fiber-optic cable is blown to 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 america from Sumitomo Electric Lightwave Corp. (Research Triangle Park, NC).]
Conduit and innerduct have one important thing in common: They facilitate pulling or replacing a cable for more capacity in the premises cabling system. However, every contractor is aware that being an installation grows, the number of cables grows to fill all of the space from the conduit. Therefore, selecting the correct trade dimension is important, since you must leave sufficient clearance between your walls of the conduit as well as other cables (begin to see the eia/tia-569 standard). Typically, conduit trade sizes range between 1/2 to 6 inches in diameter. Minimum conduit size suggested 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 total amount (as a percentage) of various kinds of cable you can use within a conduit. “The NEC typically covers power cables,” says Stewart. “Rich in-voltage cables, you will need to consider temperature and impedance, which really don`t apply in the case of data cables in conduit. The genuine question for data cable is: Is it possible to pull it into the actual size of duct that you`ve selected?”
“The most crucial decision when installing conduit is how big the conduit and clearance from your wall,” says Clawson. For external use, we use 4-inch PVC conduit, and we try and install all the conduit within the trenches while we can for future use.”
Cables are continually included in 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 inside the conduit. One method to provide for future changes is always to subdivide larger conduits with innerducts, that are smaller in diameter than conduit, generally nonmetallic, and semiflexible.
“In a existing structure, many installers usually do not want to pull new cable over the cable already from the conduit,” says Stewart, “because they risk damaging the current cable. To optimize a larger conduit, they`ll install several smaller innerducts within it. They`ll pull a smaller 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 use up space in just 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, and another spare. What you wish to do is pull as much dexlpky51 you may at installation time.”
Typically created from thermoplastic materials, innerduct has a pull string already installed. It is available in ribbed-, corrugated-, and smooth-wall styles. Some types have prelubricated inside walls. These special coatings as well as the physical properties of the inner wall of 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 produced from high-density polyethylene, it is typically employed 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 is the fact that cable jacket is “lifted” from and it has a lesser part of contact with the pipe, decreasing the coefficient of friction. However the principle is: the greater the hole, the better it`s gonna be to tug the cable,” he says.
Based on Clawson, “We use ribbed innerduct if we`re pulling one innerduct, because it`s simpler to handle. If we`re pulling via a directional boring machine and it`s a multiple pull, then we use smooth innerduct. It can be much easier to pull smooth innerduct on top of an effortless surface, plus 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 and also to install the innerduct with all the appropriate support. If the innerduct is secured with tie wraps within a plenum area, always use plenum-rated products.
Innerduct is normally offered in one color–orange to the 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. “There exists a movement afoot in order to use color designations for various applications,” says Stewart. “Orange is generally communications, red will be for power, and yellow for gas.”