In outside-plant installations, conduit is generally installed underground to guard cables from damage and also 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 such as in the telecommunications closet (TC) to operate-area outlets, or from an equipment room to your TC. To safeguard, 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 through which cables might be pulled. Moreover, although conduit could be used to house many types of cable, the National Electrical Code (NEC) uses the phrase “optical fiber raceway” in Article 770 to describe conduit, or raceways, for optical-fiber cable. Several types of conduit can be purchased, like electrical metallic tubing (EMT), rigid metal conduit, PVC, fiberglass, and versatile conduit. For premises installations, how-ever, metal flexible conduit is not really recommended due to potential abrasion injury to the cable jacketing.
Metal conduit, which typically will come in 10-foot lengths, is rather rigid and requires special tooling and accessories to sign up for it. Nonmetallic conduit is available on reels in longer, continuous lengths which do not must be joined as frequently.
“The only problem with installing EMT conduit is it needs a special skill set and training, along with plenty of practice–or you wind up making swing sets,” explains Kevin Smith, project manager at MTS Services (Bedford, NH). “Metal conduit comes in 10-foot lengths so you have to do any nonstandard bends yourself, and that`s in which the technician`s special skill is necessary.”
Arnco Corp. (Elyria, OH) sells innerduct on the cable-TV, telecommunications, and electric utility markets, says Tom Stewart, electrical products sales manager. “Inside a building, several types of duct are employed–for example, riser- and plenum-rated–but all our products are manufactured from thermoplastic materials, including polyvinylide fluoride [pvdf] and polyvinyl chloride [pvc]. The thermoplastic materials are easier to install than metal.”
There are actually three various sorts (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 necessarily rated. Then there`s a riser product, rated by Underwriters Laboratories [UL], that is generally a thermoplastic material for example polyethylene or PVC with fire-retardant chemicals included with it. As well as the third sort of duct is UL plenum-rated, generally a pvdf product, that is fire-retardant and smoke-resistant,” says Jensen.
As outlined by Mike D`Errico, regional director of sales at Pyramid Industries (Erie, PA), most goods that conduit and innerduct manufacturers make is for outside plant. Some manufacturers offer prelubricated innerduct and conduit, “frequently incorporating some form of silicon,” he says. “For premises cabling, Pyramid delivers a plenum raceway (tested to UL-910) plus a riser raceway (UL-1666) for installation in vertical shafts.” Additionally, the riser item is halogen-free which is often useful for military, shipboard, or tunnel applications, depending on the specifications.
Naturally contractors install conduit where building codes require it, and also where the cabling system needs physical protection or protection from unauthorized access.
“We use conduit in riser and backbone systems from the building entrance towards the main distribution frame,” says Karl Clawson, senior v . p . and partner, Clawson Communications (Greenwood, IN). “And that we also do the installation for horizontal cabling, particularly in university campuses. Inside the living quarters, we install cable in conduit since 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; as an example, electricians that have more experience in performing this task. “Generally, the only real time we use Plastic Flexible Conduit is when we`re creating a riser or penetrating a fire wall,” says Smith. “Typically, we may not install conduit from the wiring closet on the workstation outlet. For brief distances, around 100 feet, we may install conduit between buildings based on the existing infrastructure.
As well as the traditional smooth-bore type, innerduct can be obtained with a ribbed inner wall to lessen friction involving the cable sheath as well as the innerduct wall. “A wave-rib on the inside of the duct reduces surface contact in between the cable and the wall of your 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 provides outerducts with pre-installed innerducts. Clawson says that, due to its cost, his company does not use conduit with pre- installed innerduct. “We keep leftover conduit in store to utilize on other jobs,” he says. “But pre-installed conduit is really a special application, so overages and underages are form of costly to manage.”
For premises applications, Dura-line (Knoxville, TN) has designed a conduit, referred to as Hex-line, for multiple-duct applications between buildings. “While you pull the ducts from the reel (two to each reel), they go deep into a collector, which Dura-line supplies free of charge,” says Ray McLeary, v . p . of sales. “Each duct features a men and women part, which are snapped together, creating a multiple duct system. This saves time, space, and funds, but the most significant savings is space.” He explains: “Normally, you may put three 1-inch innerducts right into a 4-inch conduit. Using this system, you may fit four 11/4-inch or six 1-inch innerducts in to the conduit.”
When choosing innerduct, you should also be worried about its tensile strength and crush resistance. “The thicker the wall material, the greater the tensile rating,” says Stewart. “If you`re planning to pull it over a cross country, pick a wall thickness that permits you to 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 else you can`t pull within the cable,” he explains.
As a result of limited amount of tensile pull that you can exert about the cable, people seek out methods to lessen the coefficient of friction within the conduit. “There are actually products out there for example prelubricated conduit,” says Stewart. “And there`s a good different technology used for placing cable, called air-blown fiber (or ABF), where the fiber-optic cable is blown to the conduit. We manufacture whatever we call the `air-trak` system–a conduit system with chambers–to be used in ABF installations.” [Air-blown fiber is available 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 within a premises cabling system. However, every contractor is aware that being an installation grows, the volume of cables grows to fill all the space within the conduit. Therefore, picking out the correct trade dimension is important, as you must leave sufficient clearance between your walls in the conduit and also other cables (start to see 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 has to be available to allow pulling the cable without excessive friction or bending.
The NEC conduit-fill tables define the amount (being a percentage) of different kinds of cable you can use in a conduit. “The NEC typically covers power cables,” says Stewart. “Rich in-voltage cables, you have to consider temperature and impedance, which really don`t apply in the case of data cables in conduit. The real question for data cable is: Are you able to pull it into the dimensions of duct that you`ve selected?”
“The most important decision when installing conduit is the actual size of the conduit and clearance from the wall,” says Clawson. For external use, we use 4-inch PVC conduit, therefore we attempt to install just as much conduit inside 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 within the conduit. A great way to look after future changes is to subdivide larger conduits with innerducts, that happen to be smaller in diameter than conduit, generally nonmetallic, and semiflexible.
“Within an existing structure, many installers usually do not wish to pull new cable within the cable already inside the conduit,” says Stewart, “since they risk damaging the current cable. To optimize a more substantial conduit, they`ll install several smaller innerducts inside it. They`ll pull a lesser fiber cable into one of many innerducts, and after that 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 two-inch innerducts are accessible for larger fiber cables. Although innerducts occupy space in just a conduit, they provide additional protection and adaptability in constantly changing cabling installations.
“Generally, if you`re installing a 4-inch conduit,” says Smith, “you`ll end up setting up three 1-inch innerducts: one for fiber, one for data, and another spare. What you should do is pull the maximum amount of dexlpky51 you may at installation time.”
Typically manufactured from thermoplastic materials, innerduct features 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 as well as the physical properties in 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 constructed from high-density polyethylene, it can be 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 Metal Flexible Conduit is that the cable jacket is “lifted” from and possesses a lesser section of connection with the pipe, decreasing the coefficient of friction. Nevertheless the rule of thumb is: the larger the hole, the better 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, then we use smooth innerduct. It can be much easier to pull smooth innerduct on the top of an easy surface, plus it doesn`t kink as easily as ribbed innerduct.”
When using innerduct, it is important to verify be it a plenum or non-plenum area and also to install the innerduct together with the appropriate support. In case the innerduct is secured with tie wraps in a plenum area, always use plenum-rated products.
Innerduct is generally offered in one color–orange for that 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 find a movement afoot to try to use color designations for various applications,” says Stewart. “Orange is generally communications, red will be for electricity, and yellow for gas.”