In outside-plant installations, conduit is usually installed underground to shield cables from damage and to facilitate cable placement for fast and future needs. You can even install Conduit Fittings inside buildings to facilitate pulling cable between two points including in the telecommunications closet (TC) to be effective-area outlets, or from an equipment room to some TC. To shield, isolate, and identify the cables, innerduct–also called subduct–could be installed inside existing larger-diameter conduit.
Conduit is defined as a rigid or flexible metal or nonmetallic raceway by which cables may be pulled. In addition, although conduit may be used to house many types 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 kinds of conduit can be found, including electrical metallic tubing (EMT), rigid metal conduit, PVC, fiberglass, and versatile conduit. For premises installations, how-ever, metal flexible conduit will not be recommended because of potential abrasion problems for the cable jacketing.
Metal conduit, which typically can be purchased in 10-foot lengths, is rather rigid and needs special tooling and accessories to sign up with it. Nonmetallic conduit is offered on reels in longer, continuous lengths which do not must be joined as frequently.
“The only issue with installing EMT conduit is that it needs a special skill set and training, along with a lot of practice–or you wind up making swing sets,” explains Kevin Smith, project manager at MTS Services (Bedford, NH). “Metal conduit can be purchased in 10-foot lengths so you need to do any nonstandard bends manually, and that`s in which the technician`s special skill is needed.”
Arnco Corp. (Elyria, OH) sells innerduct for the cable-TV, telecommunications, and electric utility markets, says Tom Stewart, electrical products sales manager. “In a building, several types of duct are being used–by way of 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 simpler to install than metal.”
You can 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 often polyethylene and it`s certainly not rated. Then there`s a riser product, rated by Underwriters Laboratories [UL], which is generally a thermoplastic material for example polyethylene or PVC with fire-retardant chemicals added to it. Along with the third form 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 goods that conduit and innerduct manufacturers make is perfect for outside plant. Some manufacturers offer prelubricated innerduct and conduit, “very often incorporating some form of silicon,” he says. “For premises cabling, Pyramid supplies a plenum raceway (tested to UL-910) as well as a riser raceway (UL-1666) for installation in vertical shafts.” In addition, the riser product is halogen-free and is often utilized for military, shipboard, or tunnel applications, depending upon the specifications.
Naturally contractors install conduit where building codes require it, and also where the cabling system needs physical protection or defense against unauthorized access.
“We use conduit in riser and backbone systems in the building entrance for 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, specifically in university campuses. From the living quarters, we install cable in conduit since it provides the cable extra protection, and hopefully, keeps it out of students` reach,” he says.
Some cabling contractors prefer to have other trades install conduit; as an example, electricians who definitely have more experience of performing this. “Generally, the sole time we use Plastic Flexible Conduit happens when we`re developing a riser or penetrating a fire wall,” says Smith. “Typically, we may not install conduit in the wiring closet on the workstation outlet. For short distances, as much as 100 feet, we would install conduit between buildings depending 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 along with the innerduct wall. “A wave-rib on the inside of the duct reduces surface contact between the cable along with the wall in the duct, thus lowering the coefficient of friction and letting you pull cable over longer distances,” says Stewart.
Another variation is definitely the multicelled conduit system, which provides outerducts with pre-installed innerducts. Clawson states that, due to 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 can be a special application, so overages and underages are kind of costly to deal with.”
For premises applications, Dura-line (Knoxville, TN) has created a conduit, known as Hex-line, for multiple-duct applications between buildings. “When you pull the ducts from the reel (two to every single reel), they go deep into a collector, which Dura-line supplies cost-free,” says Ray McLeary, vice president of sales. “Each duct has a male and female part, that are snapped together, making 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. Using this type of system, it is possible to fit four 11/4-inch or six 1-inch innerducts into the conduit.”
When buying innerduct, you also need to be worried about its tensile strength and crush resistance. “The thicker the wall material, the greater the tensile rating,” says Stewart. “If you`re going to pull it over a long-distance, decide on a wall thickness that lets you pull the duct over that distance. The crush-resistance feature helps to make sure that the innerduct won`t be damaged in the placing process–or else you can`t pull in the cable,” he explains.
Because of the limited quantity of tensile pull that one could exert about the cable, people look for methods to reduce the coefficient of friction inside the conduit. “You can find products available on the market such as prelubricated conduit,” says Stewart. “And there`s even a different technology being used for placing cable, generally known as air-blown fiber (or ABF), the location where the fiber-optic cable is blown in 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 a very important factor in common: They facilitate pulling or replacing a cable for more capacity within a premises cabling system. However, every contractor understands that for an installation grows, the amount of cables grows to fill each of the space within the conduit. Therefore, choosing the correct trade size is important, since you must leave sufficient clearance between the walls from the conduit and other cables (see 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 should be offered to allow pulling the cable without excessive friction or bending.
The NEC conduit-fill tables define the amount (as being a percentage) of several types of cable you may use in the conduit. “The NEC typically covers power cables,” says Stewart. “With higher-voltage cables, you have 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: Could you pull it into the size of duct that you`ve selected?”
“The most crucial decision when installing conduit is the size of the conduit and clearance through the wall,” says Clawson. For external use, we use 4-inch PVC conduit, therefore we try to install the maximum amount of conduit in the trenches since 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 may damage existing cables within the conduit. One method to offer future changes is always to subdivide larger conduits with innerducts, that happen to be smaller in diameter than conduit, generally nonmetallic, and semiflexible.
“In a existing structure, many installers do not want to pull new cable on the cable already within the conduit,” says Stewart, “mainly 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 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 normally used within buildings; however, 11/4-, 11/2-, and two-inch innerducts are accessible for larger fiber cables. Although innerducts occupy space inside a conduit, they offer additional protection and adaptability in constantly changing cabling installations.
“Generally, if you`re installing a 4-inch conduit,” says Smith, “you`ll turn out investing in three 1-inch innerducts: one for fiber, one for data, and something spare. What for you to do is pull as much dexlpky51 you are able to at installation time.”
Typically produced 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 and the physical properties in the inner wall in the innerduct ensure less friction and tension when pulling cable.
“Corrugated innerduct is used in plenum and riser products,” says D`Errico. “And, when constructed from high-density polyethylene, it is typically employed for short–1000 feet or less–installations.” Smooth wall is commonly used for direct-buried, trenching, plowing, aerial, and directional boring applications. “The Flexible Metal Conduit Pipe is that the cable jacket is “lifted” far from and contains a reduced section of contact with the pipe, lowering the coefficient of friction. Nevertheless the general guideline is: the larger the hole, the easier it`s going to be to tug 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 quicker to pull smooth innerduct on the top of an even surface, and it also doesn`t kink as easily as ribbed innerduct.”
When using innerduct, it is essential to verify whether it be a plenum or non-plenum area as well as install the innerduct with all the appropriate support. When the innerduct is secured with tie wraps in the plenum area, always use plenum-rated products.
Innerduct is usually offered in a color–orange for that fiber-optic communications industry. Color can occasionally be installation-specific; for instance, one color for data cable, one for telephone, and the like. “You will discover a movement afoot to try to use color designations for various types of applications,” says Stewart. “Orange is normally communications, red would be for electrical power, and yellow for gas.”