In outside-plant installations, conduit is usually installed underground to shield 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 like from your telecommunications closet (TC) to operate-area outlets, or from an equipment room to your TC. To guard, isolate, and identify the cables, innerduct–also called subduct–might be installed inside existing larger-diameter conduit.
Conduit is described as a rigid or flexible metal or nonmetallic raceway whereby cables might be pulled. Furthermore, although conduit could be used to house various kinds of cable, the National Electrical Code (NEC) uses the expression “optical fiber raceway” in Article 770 to illustrate conduit, or raceways, for optical-fiber cable. Various kinds conduit are available, for example electrical metallic tubing (EMT), rigid metal conduit, PVC, fiberglass, and flexible conduit. For premises installations, how-ever, metal flexible conduit is not recommended because of potential abrasion damage to the cable jacketing.
Metal conduit, which typically is available 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 really need to be joined as much.
“The only problem with installing EMT conduit is that it requires a special skill set and training, along with a great deal 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 by hand, and that`s where 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. “Within a building, several kinds of duct are being used–by way of example, riser- and plenum-rated–but all our products are produced 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 normally polyethylene and it`s not really rated. Then there`s a riser product, rated by Underwriters Laboratories [UL], which is generally a thermoplastic material like polyethylene or PVC with fire-retardant chemicals included with it. Along with the third type of duct is UL plenum-rated, generally a pvdf product, which happens to be fire-retardant and smoke-resistant,” says Jensen.
As outlined by Mike D`Errico, regional director of sales at Pyramid Industries (Erie, PA), most items that conduit and innerduct manufacturers make is for outside plant. Some manufacturers offer prelubricated innerduct and conduit, “fairly often incorporating some kind of silicon,” he says. “For premises cabling, Pyramid supplies a plenum raceway (tested to UL-910) plus a riser raceway (UL-1666) for installation in vertical shafts.” Furthermore, the riser product is halogen-free and is often utilized for military, shipboard, or tunnel applications, depending upon the specifications.
Of course contractors install conduit where building codes require it, and also where cabling system needs physical protection or defense against unauthorized access.
“We use conduit in riser and backbone systems through the building entrance on the main distribution frame,” says Karl Clawson, senior v . p . and partner, Clawson Communications (Greenwood, IN). “So we also install it for horizontal cabling, specifically in university campuses. In 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 that have more experience with performing this task. “Generally, the only time we use Plastic Flexible Conduit happens when we`re creating a riser or penetrating a fire wall,” says Smith. “Typically, we would not install conduit from your wiring closet towards the workstation outlet. For short distances, as much as 100 feet, we might install conduit between buildings based on the existing infrastructure.
Along with the traditional smooth-bore type, innerduct is accessible having a ribbed inner wall to lessen friction between the cable sheath as well as the innerduct wall. “A wave-rib on the inside of the duct reduces surface contact between your cable and the wall in the duct, thus reducing the coefficient of friction and helping you to pull cable over longer distances,” says Stewart.
Another variation may be the multicelled conduit system, which offers outerducts with pre-installed innerducts. Clawson states that, due to its cost, his company will not use conduit with pre- installed innerduct. “We keep leftover conduit in stock to utilize on other jobs,” he says. “But pre-installed conduit can be a special application, so overages and underages are sort of costly to manage.”
For premises applications, Dura-line (Knoxville, TN) has designed a conduit, known as Hex-line, for multiple-duct applications between buildings. “As you may pull the ducts away from the reel (two to 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 female and male part, which can be snapped together, building a multiple duct system. This saves time, space, and money, but the main savings is space.” He explains: “Normally, you can put three 1-inch innerducts right into a 4-inch conduit. Using this type of system, you are able to fit four 11/4-inch or six 1-inch innerducts into the conduit.”
When purchasing innerduct, you also need to be worried about its tensile strength and crush resistance. “The thicker the wall material, the higher the tensile rating,” says Stewart. “If you`re planning to pull it over a long-distance, choose 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 through the placing process–or else you can`t pull inside the cable,” he explains.
As a result of limited level of tensile pull that one could exert on the cable, people try to find approaches to reduce the coefficient of friction inside of the conduit. “You will find products in the marketplace including prelubricated conduit,” says Stewart. “And there`s also a different technology used for placing cable, called air-blown fiber (or ABF), where the fiber-optic cable is blown into the conduit. We manufacture what we call the `air-trak` system–a conduit system with chambers–for use 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 one thing in common: They facilitate pulling or replacing a cable for added capacity in the premises cabling system. However, every contractor is aware that as being an installation grows, the quantity of cables grows to fill all the space from the conduit. Therefore, choosing the correct trade dimension is important, since you must leave sufficient clearance between your walls from the conduit and other cables (start to see the eia/tia-569 standard). Typically, conduit trade sizes cover anything from 1/2 to 6 inches in diameter. Minimum conduit size suitable for backbone cables is 4 inches. Sufficient clearance needs to 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 various kinds of cable you should use in the conduit. “The NEC typically covers power cables,” says Stewart. “With high-voltage cables, you will need to consider temperature and impedance, which really don`t apply in the matter of data cables in conduit. The real question for data cable is: Is it possible to pull it into the actual size of duct that you`ve selected?”
“The most crucial 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, and we attempt to install the maximum amount of conduit from the trenches while we can for future use.”
Cables are continually put into 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 inside of the conduit. A great way to offer future changes is usually 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 tend not to would like to pull new cable over the cable already from the conduit,” says Stewart, “simply because they risk damaging the current cable. To optimize a more substantial conduit, they`ll install several smaller innerducts inside it. They`ll pull a reduced fiber cable into among the 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 normally used within buildings; however, 11/4-, 11/2-, and 2-inch innerducts are around for larger fiber cables. Although innerducts occupy space within a conduit, they give additional protection and adaptability in constantly changing cabling installations.
“Generally, if you`re installing a 4-inch conduit,” says Smith, “you`ll find yourself setting up three 1-inch innerducts: one for fiber, one for data, and one spare. What you want to do is pull the maximum amount of dexlpky51 you are able to at installation time.”
Typically constructed from thermoplastic materials, innerduct features 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 along with the physical properties from the inner wall of the innerduct ensure less friction and tension when pulling cable.
“Corrugated innerduct is utilized in plenum and riser products,” says D`Errico. “And, when produced from high-density polyethylene, it really is 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” clear of and possesses a smaller area of experience of the pipe, decreasing the coefficient of friction. Nevertheless the general guideline is: the greater the hole, the better it`s going to be to drag the cable,” he says.
In accordance with Clawson, “We use ribbed innerduct if we`re pulling one innerduct, because it`s quicker to handle. If we`re pulling via a directional boring machine and it`s a multiple pull, we use smooth innerduct. It can be easier to pull smooth innerduct in addition to an easy surface, and yes it doesn`t kink as easily as ribbed innerduct.”
When you use innerduct, you should verify whether it is a plenum or non-plenum area as well as to install the innerduct with the appropriate support. When the innerduct is secured with tie wraps in a plenum area, only use plenum-rated products.
Innerduct is usually offered in a color–orange for the fiber-optic communications industry. Color is often installation-specific; for example, one color for data cable, one for telephone, and so forth. “You will discover a movement afoot to try to use color designations for various applications,” says Stewart. “Orange is generally communications, red can be for power, and yellow for gas.”