In outside-plant installations, conduit is usually installed underground to guard cables from damage and to facilitate cable placement for fast and future needs. You can also install Conduit Fittings Wholesale inside buildings to facilitate pulling cable between two points like from the telecommunications closet (TC) to be effective-area outlets, or from an equipment room to a TC. To guard, isolate, and identify the cables, innerduct–also called subduct–may be installed inside existing larger-diameter conduit.
Conduit is defined as a rigid or flexible metal or nonmetallic raceway through which cables might be pulled. Furthermore, although conduit could be used to house various kinds of cable, the National Electrical Code (NEC) uses the word “optical fiber raceway” in Article 770 to clarify conduit, or raceways, for optical-fiber cable. Various kinds conduit can be purchased, for example electrical metallic tubing (EMT), rigid metal conduit, PVC, fiberglass, and versatile conduit. For premises installations, how-ever, metal flexible conduit will not be recommended as a result of potential abrasion harm to the cable jacketing.
Metal conduit, which typically is available in 10-foot lengths, is rather rigid and requires special tooling and accessories to join it. Nonmetallic conduit is offered on reels in longer, continuous lengths which do not have to be joined as much.
“One problem with installing EMT conduit is that it takes a special skill set and training, as well as a lot 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 should do any nonstandard bends yourself, and that`s in which the technician`s special skill is important.”
Arnco Corp. (Elyria, OH) sells innerduct towards the cable-TV, telecommunications, and electric utility markets, says Tom Stewart, electrical products sales manager. “In the building, various kinds of duct are employed–by way of example, riser- and plenum-rated–but all of our products are manufactured from thermoplastic materials, for example polyvinylide fluoride [pvdf] and polyvinyl chloride [pvc]. The thermoplastic materials are easier to install than metal.”
There are actually 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 generally polyethylene and it`s not really rated. Then there`s a riser product, rated by Underwriters Laboratories [UL], which is generally a thermoplastic material including polyethylene or PVC with fire-retardant chemicals added to it. Along with the third type 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 designed for outside plant. Some manufacturers offer prelubricated innerduct and conduit, “fairly often incorporating some type of silicon,” he says. “For premises cabling, Pyramid provides a plenum raceway (tested to UL-910) along with a riser raceway (UL-1666) for installation in vertical shafts.” Additionally, the riser item is halogen-free and is often employed for military, shipboard, or tunnel applications, based on the specifications.
Needless to say contractors install conduit where building codes require it, but in addition in which the cabling system needs physical protection or protection from unauthorized access.
“We use conduit in riser and backbone systems from your building entrance to the main distribution frame,” says Karl Clawson, senior v . p . and partner, Clawson Communications (Greenwood, IN). “And we also install it for horizontal cabling, specifically in university campuses. Inside the living quarters, we install cable in conduit as it allows the cable extra protection, and hopefully, keeps it of students` reach,” he says.
Some cabling contractors choose to have other trades install conduit; by way of example, electricians who may have more experience with performing this task. “Generally, the only real time we use Flexible Plastic Conduit for Cables is when we`re creating a riser or penetrating a fire wall,” says Smith. “Typically, we would not install conduit through the wiring closet for the workstation outlet. For brief distances, up to 100 feet, we may install conduit between buildings according to the existing infrastructure.
Along with the traditional smooth-bore type, innerduct is available having a ribbed inner wall to lessen friction in between the cable sheath along with the innerduct wall. “A wave-rib within the duct reduces surface contact in between the cable and also the wall of your duct, thus decreasing the coefficient of friction and enabling you to pull cable over longer distances,” says Stewart.
Another variation will be the multicelled conduit system, that offers outerducts with pre-installed innerducts. Clawson says 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 type of costly to deal with.”
For premises applications, Dura-line (Knoxville, TN) has designed a conduit, called Hex-line, for multiple-duct applications between buildings. “While you pull the ducts off the reel (two to every reel), they go deep into a collector, which Dura-line supplies free of cost,” says Ray McLeary, v . p . of sales. “Each duct carries 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 can put three 1-inch innerducts in to a 4-inch conduit. With this system, you may fit four 11/4-inch or six 1-inch innerducts to the conduit.”
When purchasing innerduct, you also need to 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 spanning a cross country, pick a wall thickness that allows you to pull the duct over that distance. The crush-resistance feature helps to make certain that the innerduct won`t be damaged through the placing process–or perhaps you can`t pull within the cable,” he explains.
Due to the limited level of tensile pull that you could exert in the cable, people try to find methods to lessen the coefficient of friction in the conduit. “There are actually products in the marketplace for example prelubricated conduit,” says Stewart. “And there`s a good different technology being used for placing cable, known as air-blown fiber (or ABF), in which the fiber-optic cable is blown in to the conduit. We manufacture everything we call the `air-trak` system–a conduit system with chambers–for use in ABF installations.” [Air-blown fiber is accessible in the United States 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 in a premises cabling system. However, every contractor is aware that as an installation grows, the quantity of cables grows to fill each of the space from the conduit. Therefore, choosing the correct trade size is important, since you must leave sufficient clearance in between the walls of your conduit and also other cables (view 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 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 use in a conduit. “The NEC typically covers power cables,” says Stewart. “With good-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: Are you able to pull it into the actual size of duct that you`ve selected?”
“The most significant decision when installing conduit is how big the conduit and clearance from the wall,” says Clawson. For external use, we use 4-inch PVC conduit, therefore we try to install just as much conduit within the trenches when we can for future use.”
Cables are continually put into 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 in the conduit. A good way to look after future changes would be to subdivide larger conduits with innerducts, which can be smaller in diameter than conduit, generally nonmetallic, and semiflexible.
“In an existing structure, many installers tend not to wish to pull new cable over the cable already from the conduit,” says Stewart, “mainly because they risk damaging the existing cable. To optimize a greater conduit, they`ll install several smaller innerducts within it. They`ll pull a lesser fiber cable into among the innerducts, after which 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 two-inch innerducts are accessible for larger fiber cables. Although innerducts use up space in just a conduit, they offer additional protection and suppleness 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, then one spare. What you should do is pull just as much dexlpky51 it is possible to at installation time.”
Typically manufactured from thermoplastic materials, innerduct has a pull string already installed. It comes 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 is utilized in plenum and riser products,” says D`Errico. “And, when created from high-density polyethylene, it is actually 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 it has a lesser section of connection with the pipe, reducing the coefficient of friction. However the rule of thumb is: the greater the hole, the easier it`s going to be to drag the cable,” he says.
As outlined by Clawson, “We use ribbed innerduct if we`re pulling one innerduct, because it`s simpler to handle. If we`re pulling via a directional boring machine and it`s a multiple pull, then we use smooth innerduct. It can be easier to pull smooth innerduct on top of a smooth surface, and yes it doesn`t kink as easily as ribbed innerduct.”
When utilizing innerduct, you should verify whether it is a plenum or non-plenum area as well as install the innerduct together with the appropriate support. In case the innerduct is secured with tie wraps inside a plenum area, always use plenum-rated products.
Innerduct is normally offered in one color–orange for the fiber-optic communications industry. Color can sometimes be installation-specific; by way of example, one color for data cable, one for telephone, etc. “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.”