In outside-plant installations, conduit is normally installed underground to safeguard cables from damage and 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 for example in the telecommunications closet (TC) to work-area outlets, or from an equipment room to some TC. To protect, isolate, and identify the cables, innerduct–also known as subduct–could be installed inside existing larger-diameter conduit.
Conduit is described as a rigid or flexible metal or nonmetallic raceway in which cables could be pulled. Moreover, although conduit enables you to house various types of cable, the National Electrical Code (NEC) uses the word “optical fiber raceway” in Article 770 to describe conduit, or raceways, for optical-fiber cable. Several types of conduit can be purchased, for example electrical metallic tubing (EMT), rigid metal conduit, PVC, fiberglass, and flexible conduit. For premises installations, how-ever, metal flexible conduit is not really recommended due to potential abrasion damage to the cable jacketing.
Metal conduit, which typically is available in 10-foot lengths, is fairly rigid and requires special tooling and accessories to join it. Nonmetallic conduit is accessible on reels in longer, continuous lengths which do not need to be joined as often.
“The only problem with installing EMT conduit is that it requires a special skill set and training, in addition to a lot of practice–or you end up making swing sets,” explains Kevin Smith, project manager at MTS Services (Bedford, NH). “Metal conduit is available in 10-foot lengths so you have to do any nonstandard bends manually, and that`s in which 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. “Inside a building, several kinds of duct are being used–for instance, riser- and plenum-rated–but all our products are produced from thermoplastic materials, such as polyvinylide fluoride [pvdf] and polyvinyl chloride [pvc]. The thermoplastic materials are simpler to install than metal.”
There are three different kinds (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 can be generally a thermoplastic material such as 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 is fire-retardant and smoke-resistant,” says Jensen.
Based on Mike D`Errico, regional director of sales at Pyramid Industries (Erie, PA), most products which conduit and innerduct manufacturers make is perfect for outside plant. Some manufacturers offer prelubricated innerduct and conduit, “frequently incorporating some sort 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 item is halogen-free and is also often useful for military, shipboard, or tunnel applications, based on the specifications.
Naturally contractors install conduit where building codes require it, and also the location where the cabling system needs physical protection or defense against unauthorized access.
“We use conduit in riser and backbone systems from the building entrance towards the main distribution frame,” says Karl Clawson, senior vice president and partner, Clawson Communications (Greenwood, IN). “So we also install it for horizontal cabling, particularly in university campuses. From the living quarters, we install cable in conduit mainly because it allows the cable extra protection, and hopefully, keeps it of students` reach,” he says.
Some cabling contractors prefer to have other trades install conduit; as an example, electricians who may have more expertise in performing this. “Generally, the only time we use Plastic Flexible Conduit occurs when we`re developing a riser or penetrating a fire wall,” says Smith. “Typically, we might not install conduit from your wiring closet on the workstation outlet. For short 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 having a ribbed inner wall to lessen friction between the cable sheath and the innerduct wall. “A wave-rib within the duct reduces surface contact in between the cable as well as the wall of the duct, thus decreasing the coefficient of friction and helping you to pull cable over longer distances,” says Stewart.
Another variation may be the multicelled conduit system, that offers outerducts with pre-installed innerducts. Clawson states that, because of its cost, his company is not going to use conduit with pre- installed innerduct. “We keep leftover conduit in stock to work with 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 created a conduit, generally known as Hex-line, for multiple-duct applications between buildings. “While you pull the ducts off of the reel (two to each and every reel), they enter into a collector, which Dura-line supplies free of charge,” says Ray McLeary, vice president of sales. “Each duct carries a men and women part, which can be snapped together, making a multiple duct system. This saves time, space, and money, but the main savings is space.” He explains: “Normally, you are able to put three 1-inch innerducts in to a 4-inch conduit. Using this system, it is possible to fit four 11/4-inch or six 1-inch innerducts to the conduit.”
When purchasing innerduct, you should also be concerned with its tensile strength and crush resistance. “The thicker the wall material, the better the tensile rating,” says Stewart. “If you`re going to pull it more than a cross country, pick a wall thickness that lets you 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 in the cable,” he explains.
Because of the limited volume of tensile pull that you could exert in the cable, people search for methods to minimize the coefficient of friction within the conduit. “There are actually products in the marketplace including prelubricated conduit,” says Stewart. “And there`s even a different technology used for placing cable, generally known as air-blown fiber (or ABF), where fiber-optic cable is blown in 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 states 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 added capacity in a premises cabling system. However, every contractor recognizes that as being an installation grows, the amount of cables grows to fill all the space from the conduit. Therefore, selecting the correct trade dimensions are important, because you must leave sufficient clearance in between the walls of the conduit as well as other cables (view 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 must be open to allow pulling the cable without excessive friction or bending.
The NEC conduit-fill tables define the quantity (like a percentage) of various kinds of cable you should use within a conduit. “The NEC typically covers power cables,” says Stewart. “With high-voltage cables, you must consider temperature and impedance, which really don`t apply in the case of data cables in conduit. The actual question for data cable is: Can 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 from your wall,” says Clawson. For external use, we use 4-inch PVC conduit, and that we attempt to install as much conduit in the trenches while we can for future use.”
Cables are continually included with conduit systems which can be often filled to capacity with generations of older cable. When new cables are added, friction and pulling tension may damage existing cables inside of the conduit. A good way to provide for future changes would be to subdivide larger conduits with innerducts, which can be smaller in diameter than conduit, generally nonmetallic, and semiflexible.
“Inside an existing structure, many installers usually do not would like to pull new cable within the cable already within the conduit,” says Stewart, “mainly because they risk damaging existing cable. To optimize a larger conduit, they`ll install several smaller innerducts inside it. They`ll pull a smaller fiber cable into one of several innerducts, and then have additional ducts for use 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 accessible for larger fiber cables. Although innerducts use up 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 turn out putting in three 1-inch innerducts: one for fiber, one for data, then one spare. What you should do is pull all the dexlpky51 it is possible to at installation time.”
Typically created from thermoplastic materials, innerduct includes 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 of the inner wall from the innerduct ensure less friction and tension when pulling cable.
“Corrugated innerduct is utilized 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 can be used for direct-buried, trenching, plowing, aerial, and directional boring applications. “The Flexible Metal Conduit Pipe is the cable jacket is “lifted” clear of and possesses a lesser part of experience of the pipe, lowering the coefficient of friction. However the guideline is: the greater the hole, the easier it`s going to be to pull the cable,” he says.
Based on Clawson, “We use ribbed innerduct if we`re pulling one innerduct, because it`s quicker to handle. If we`re pulling by way of a directional boring machine and it`s a multiple pull, we use smooth innerduct. It is actually simpler 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 be it a plenum or non-plenum area as well as install the innerduct together with the appropriate support. In the event the innerduct is secured with tie wraps inside a plenum area, always employ plenum-rated products.
Innerduct is generally offered in a single color–orange for your fiber-optic communications industry. Color can sometimes be installation-specific; for example, one color for data cable, one for telephone, and so on. “There is a movement afoot in order to use color designations for various applications,” says Stewart. “Orange is normally communications, red could be for electricity, and yellow for gas.”