In outside-plant installations, conduit is generally installed underground to guard cables from damage as well as to facilitate cable placement for immediate and future needs. You can even install Conduit Fittings Wholesale inside buildings to facilitate pulling cable between two points like through the telecommunications closet (TC) to function-area outlets, or from an equipment room to your TC. To protect, isolate, and identify the cables, innerduct–often known as subduct–could 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. Additionally, although conduit could be used to house various types 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. Several kinds of conduit are available, such as electrical metallic tubing (EMT), rigid metal conduit, PVC, fiberglass, and flexible conduit. For premises installations, how-ever, metal flexible conduit will not be recommended as a consequence of potential abrasion problems for the cable jacketing.
Metal conduit, which typically will come in 10-foot lengths, is pretty rigid and needs special tooling and accessories to sign up with it. Nonmetallic conduit is accessible on reels in longer, continuous lengths that do not need to be joined as much.
“One problem with installing EMT conduit is it demands a special skill set and training, in addition to plenty of practice–or you find yourself 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 manually, and that`s the location where the technician`s special skill is important.”
Arnco Corp. (Elyria, OH) sells innerduct for the cable-TV, telecommunications, and electric utility markets, says Tom Stewart, electrical products sales manager. “Within a building, several kinds of duct are employed–by way of 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.”
You will find 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 definitely not rated. Then there`s a riser product, rated by Underwriters Laboratories [UL], which can be generally a thermoplastic material like polyethylene or PVC with fire-retardant chemicals put into it. And the third kind of duct is UL plenum-rated, generally a pvdf product, which happens to be fire-retardant and smoke-resistant,” says Jensen.
According to 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, “fairly 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.” Additionally, the riser product is halogen-free which is often utilized for military, shipboard, or tunnel applications, based on the specifications.
Needless to say 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 in the building entrance on the main distribution frame,” says Karl Clawson, senior vice president and partner, Clawson Communications (Greenwood, IN). “Therefore we also install it for horizontal cabling, particularly in university campuses. From the living quarters, we install cable in conduit mainly because it gives the cable extra protection, and hopefully, keeps it of students` reach,” he says.
Some cabling contractors choose to have other trades install conduit; as an example, electricians who may have more experience of performing this task. “Generally, really the only time we use Plastic Flexible Conduit takes place when we`re developing a riser or penetrating a fire wall,” says Smith. “Typically, we may not install conduit from the wiring closet on the workstation outlet. For short distances, just as much as 100 feet, we will install conduit between buildings depending on the existing infrastructure.
Besides the traditional smooth-bore type, innerduct is accessible using a ribbed inner wall to minimize friction between your cable sheath and the innerduct wall. “A wave-rib on the inside of the duct reduces surface contact between your cable and the wall from the duct, thus decreasing the coefficient of friction and enabling you to pull cable over longer distances,” says Stewart.
Another variation is the multicelled conduit system, that offers outerducts with pre-installed innerducts. Clawson states that, due to the cost, his company does not use conduit with pre- installed innerduct. “We keep leftover conduit in stock to make use of on other jobs,” he says. “But pre-installed conduit can be a special application, so overages and underages are sort of costly to deal with.”
For premises applications, Dura-line (Knoxville, TN) has created a conduit, called Hex-line, for multiple-duct applications between buildings. “As you may pull the ducts away from the reel (two to each and every reel), they go into a collector, which Dura-line supplies free of charge,” says Ray McLeary, v . p . of sales. “Each duct features a male and female part, which are snapped together, making a multiple duct system. This saves time, space, and funds, but the most important savings is space.” He explains: “Normally, you can put three 1-inch innerducts into a 4-inch conduit. Using this type of system, you can fit four 11/4-inch or six 1-inch innerducts in to the conduit.”
When choosing innerduct, you also have to be concerned with its tensile strength and crush resistance. “The thicker the wall material, the greater the tensile rating,” says Stewart. “If you`re likely to pull it over a long-distance, pick a wall thickness that allows you to pull the duct over that distance. The crush-resistance feature helps to ensure that the innerduct won`t be damaged during the placing process–or perhaps you can`t pull from the cable,” he explains.
As a result of limited quantity of tensile pull that one could exert on the cable, people try to find strategies to lessen the coefficient of friction inside of the conduit. “There are actually products out there for example prelubricated conduit,” says Stewart. “And there`s also a different technology getting used for placing cable, generally known as air-blown fiber (or ABF), where fiber-optic cable is blown to the conduit. We manufacture what we 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 something in common: They facilitate pulling or replacing a cable for more capacity in the premises cabling system. However, every contractor is aware that for an installation grows, the amount of cables grows to fill every one of the space in the conduit. Therefore, picking out the correct trade size is important, as you must leave sufficient clearance between the walls in the conduit along with other cables (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 total amount (as being a percentage) of different kinds of cable you should use in a conduit. “The NEC typically covers power cables,” says Stewart. “With good-voltage cables, you 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: Could you pull it into the dimensions of duct that you`ve selected?”
“The most significant 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 that we attempt to install all the conduit from the trenches as 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 can harm existing cables inside of the conduit. One method to provide for future changes would be 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 will not desire to pull new cable within the cable already in the conduit,” says Stewart, “simply because they risk damaging the present cable. To optimize a greater conduit, they`ll install several smaller innerducts within it. They`ll pull a reduced fiber cable into among the innerducts, and then have additional ducts to be utilized 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 2-inch innerducts are around for larger fiber cables. Although innerducts consume space inside a conduit, they offer 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 all the dexlpky51 you may at installation time.”
Typically manufactured from thermoplastic materials, innerduct includes a pull string already installed. It can be purchased in ribbed-, corrugated-, and smooth-wall styles. Some types have prelubricated inside walls. These special coatings and also the physical properties from 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 can be typically employed for short–1000 feet or less–installations.” Smooth wall is utilized for direct-buried, trenching, plowing, aerial, and directional boring applications. “The Metal Flexible Conduit would be that the cable jacket is “lifted” from and has a lesser area of contact with the pipe, reducing the coefficient of friction. Although the principle is: the larger the hole, the simpler it`s will be to tug the cable,” he says.
As outlined by Clawson, “We use ribbed innerduct if we`re pulling one innerduct, because it`s easier to handle. If we`re pulling through a directional boring machine and it`s a multiple pull, then we use smooth innerduct. It really is easier to pull smooth innerduct in addition to an effortless surface, plus it doesn`t kink as easily as ribbed innerduct.”
When working with innerduct, it is essential to verify be it a plenum or non-plenum area and also to install the innerduct together with the appropriate support. In the event the innerduct is secured with tie wraps inside a plenum area, only use plenum-rated products.
Innerduct is often offered in a color–orange for the fiber-optic communications industry. Color can sometimes be installation-specific; as an example, one color for data cable, one for telephone, and so on. “There exists a movement afoot in order to use color designations for various applications,” says Stewart. “Orange is generally communications, red can be for electricity, and yellow for gas.”