In outside-plant installations, conduit is typically installed underground to safeguard cables from damage and also to facilitate cable placement for fast and future needs. You may also install Conduit Fittings Wholesale inside buildings to facilitate pulling cable between two points such as from the telecommunications closet (TC) to be effective-area outlets, or from an equipment room into a TC. To protect, isolate, and identify the cables, innerduct–often known as subduct–can be installed inside existing larger-diameter conduit.
Conduit is identified as a rigid or flexible metal or nonmetallic raceway in which cables may be pulled. In addition, although conduit may be used to house various kinds of cable, the National Electrical Code (NEC) uses the term “optical fiber raceway” in Article 770 to illustrate conduit, or raceways, for optical-fiber cable. Various kinds of conduit can be found, 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 because of potential abrasion harm to the cable jacketing.
Metal conduit, which typically is available 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 have to be joined as often.
“The only issue with installing EMT conduit is that it requires a special skill set and training, in addition to lots of practice–or you end up making swing sets,” explains Kevin Smith, project manager at MTS Services (Bedford, NH). “Metal conduit comes in 10-foot lengths so you must do any nonstandard bends by hand, and that`s the location where the technician`s special skill is essential.”
Arnco Corp. (Elyria, OH) sells innerduct to the cable-TV, telecommunications, and electric utility markets, says Tom Stewart, electrical products sales manager. “Within a building, various kinds of duct are utilized–for example, riser- and plenum-rated–but all of 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 often polyethylene and it`s not really rated. Then there`s a riser product, rated by Underwriters Laboratories [UL], that is generally a thermoplastic material like polyethylene or PVC with fire-retardant chemicals included with it. And also the third kind of duct is UL plenum-rated, generally a pvdf product, which happens to 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 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 also in which the cabling system needs physical protection or defense against unauthorized access.
“We use conduit in riser and backbone systems from the building entrance to the main distribution frame,” says Karl Clawson, senior vice president and partner, Clawson Communications (Greenwood, IN). “So we also do the installation for horizontal cabling, especially in university campuses. Within the living quarters, we install cable in conduit since it gives the cable extra protection, and hopefully, keeps it of students` reach,” he says.
Some cabling contractors want to have other trades install conduit; by way of example, electricians who have more experience with performing this. “Generally, really the only time we use Flexible Plastic Conduit for Cables takes place when we`re developing a riser or penetrating a fire wall,” says Smith. “Typically, we will not install conduit in the wiring closet to the workstation outlet. In short distances, around 100 feet, we would install conduit between buildings depending on the existing infrastructure.
Along with the traditional smooth-bore type, innerduct is accessible having a ribbed inner wall to minimize friction between the cable sheath and the innerduct wall. “A wave-rib within the duct reduces surface contact between the cable as well as the wall of the duct, thus lowering the coefficient of friction and enabling you to pull cable over longer distances,” says Stewart.
Another variation will be the multicelled conduit system, which offers 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 available to make use of on other jobs,” he says. “But pre-installed conduit is really 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, known as Hex-line, for multiple-duct applications between buildings. “While you pull the ducts off the reel (two to every reel), they go into a collector, which Dura-line supplies free of cost,” says Ray McLeary, vice president of sales. “Each duct features a men and women 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, it is possible to put three 1-inch innerducts into a 4-inch conduit. Using this system, you can fit four 11/4-inch or six 1-inch innerducts in to the conduit.”
When selecting innerduct, you should also be concerned with its tensile strength and crush resistance. “The thicker the wall material, the higher the tensile rating,” says Stewart. “If you`re gonna pull it spanning a long distance, pick a wall thickness that permits you to pull the duct over that distance. The crush-resistance feature helps to make sure that the innerduct won`t be damaged through the placing process–or you can`t pull from the cable,” he explains.
Due to limited quantity of tensile pull that you can exert on the cable, people try to find strategies to lessen the coefficient of friction inside of the conduit. “You will find products out there including prelubricated conduit,” says Stewart. “And there`s also a different technology being used for placing cable, referred to as air-blown fiber (or ABF), where fiber-optic cable is blown in 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 can be obtained in the usa 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 additional capacity inside a premises cabling system. However, every contractor is aware that being an installation grows, the volume of cables grows to fill all the space from the conduit. Therefore, picking out the correct trade size is important, as you must leave sufficient clearance between the walls in the conduit and also other cables (view the eia/tia-569 standard). Typically, conduit trade sizes vary from 1/2 to 6 inches in diameter. Minimum conduit size suitable 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 amount (as being a percentage) of different kinds of cable you can utilize in a conduit. “The NEC typically covers power cables,” says Stewart. “With high-voltage cables, you need to consider temperature and impedance, which really don`t apply in the matter of data cables in conduit. The actual question for data cable is: Could you pull it into the size of duct that you`ve selected?”
“The most important decision when installing conduit is how big the conduit and clearance through the wall,” says Clawson. For external use, we use 4-inch PVC conduit, and that we try and install as much conduit within the trenches as we can for future use.”
Cables are continually added to conduit systems which can be often filled to capacity with generations of older cable. When new cables are added, friction and pulling tension can harm existing cables inside of the conduit. A great way to provide for future changes is always to subdivide larger conduits with innerducts, which are smaller in diameter than conduit, generally nonmetallic, and semiflexible.
“Inside an existing structure, many installers usually do not would like to pull new cable across 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 inside it. They`ll pull a lesser fiber cable into among 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 occupy space in just a conduit, they provide additional protection and flexibility 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 want to do is pull as much dexlpky51 you may at installation time.”
Typically constructed 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 in the innerduct ensure less friction and tension when pulling cable.
“Corrugated innerduct is commonly used in plenum and riser products,” says D`Errico. “And, when manufactured 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 is the cable jacket is “lifted” away from and possesses a reduced section of experience of the pipe, decreasing the coefficient of friction. Although the rule of thumb is: the larger the hole, the easier it`s going to be to pull 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 really is quicker to pull smooth innerduct in addition to a smooth surface, and yes it doesn`t kink as easily as ribbed innerduct.”
When working with innerduct, you should verify whether it is a plenum or non-plenum area as well as install the innerduct using the appropriate support. If the innerduct is secured with tie wraps in the plenum area, only use plenum-rated products.
Innerduct is normally offered in just one color–orange for that fiber-optic communications industry. Color can often be installation-specific; for instance, one color for data cable, one for telephone, and the like. “There exists a movement afoot to try to use color designations for various applications,” says Stewart. “Orange is normally communications, red could be for electric power, and yellow for gas.”