In outside-plant installations, conduit is usually installed underground to shield cables from damage as well as facilitate cable placement for immediate and future needs. Also you can install Conduit Fittings Wholesale inside buildings to facilitate pulling cable between two points for example from your telecommunications closet (TC) to function-area outlets, or from an equipment room to some TC. To protect, isolate, and identify the cables, innerduct–also referred to as subduct–might be installed inside existing larger-diameter conduit.
Conduit is defined as a rigid or flexible metal or nonmetallic raceway whereby cables can be pulled. Furthermore, although conduit enables you to house many types of cable, the National Electrical Code (NEC) uses the expression “optical fiber raceway” in Article 770 to explain conduit, or raceways, for optical-fiber cable. Several types of conduit are available, including electrical metallic tubing (EMT), rigid metal conduit, PVC, fiberglass, and versatile conduit. For premises installations, how-ever, metal flexible conduit is not recommended as a consequence of 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 sign up for it. Nonmetallic conduit can be obtained on reels in longer, continuous lengths that do not really need to be joined as frequently.
“A possible problem with installing EMT conduit is it takes a special skill set and training, as well as lots 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 need to do any nonstandard bends by hand, and that`s where technician`s special skill is essential.”
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, various kinds duct are employed–for example, riser- and plenum-rated–but all of 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 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 normally polyethylene and it`s not really rated. Then there`s a riser product, rated by Underwriters Laboratories [UL], which can be generally a thermoplastic material including polyethylene or PVC with fire-retardant chemicals included in it. Along with the third sort of duct is UL plenum-rated, generally a pvdf product, which can be 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 for outside plant. Some manufacturers offer prelubricated innerduct and conduit, “very often incorporating some form of silicon,” he says. “For premises cabling, Pyramid offers a plenum raceway (tested to UL-910) and a riser raceway (UL-1666) for installation in vertical shafts.” In addition, the riser item is halogen-free and is often useful for military, shipboard, or tunnel applications, depending on the specifications.
Needless to say contractors install conduit where building codes require it, but additionally in which the cabling system needs physical protection or protection from unauthorized access.
“We use conduit in riser and backbone systems through the building entrance towards the main distribution frame,” says Karl Clawson, senior v . p . and partner, Clawson Communications (Greenwood, IN). “And we also set it up for horizontal cabling, specially in university campuses. Inside the living quarters, we install cable in conduit because it allows the cable extra protection, and hopefully, keeps it out of students` reach,” he says.
Some cabling contractors want to have other trades install conduit; as an example, electricians who have more experience of performing this task. “Generally, the only real time we use Flexible Plastic Conduit for Cables occurs when we`re creating a riser or penetrating a fire wall,” says Smith. “Typically, we may not install conduit from your wiring closet towards the workstation outlet. In short distances, around 100 feet, we would install conduit between buildings according to the existing infrastructure.
As well as the traditional smooth-bore type, innerduct is available having a ribbed inner wall to lower friction in between the cable sheath and also the innerduct wall. “A wave-rib on the inside of the duct reduces surface contact between your cable and also the wall in the duct, thus lowering the coefficient of friction and enabling you to pull cable over longer distances,” says Stewart.
Another variation is definitely the multicelled conduit system, that offers outerducts with pre-installed innerducts. Clawson says that, due to the cost, his company fails to use conduit with pre- installed innerduct. “We keep leftover conduit in store 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 deal with.”
For premises applications, Dura-line (Knoxville, TN) has created a conduit, referred to as Hex-line, for multiple-duct applications between buildings. “As you may pull the ducts off of the reel (two to each and every reel), they get into a collector, which Dura-line supplies free of cost,” says Ray McLeary, v . p . of sales. “Each duct has a men and women part, that happen to be snapped together, building a multiple duct system. This saves time, space, and money, but the most crucial savings is space.” He explains: “Normally, you are able to 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 into the conduit.”
When choosing innerduct, you should also be worried about its tensile strength and crush resistance. “The thicker the wall material, the greater the tensile rating,” says Stewart. “If you`re planning to pull it over a long distance, decide on a wall thickness that permits you to pull the duct over that distance. The crush-resistance feature helps to ensure the innerduct won`t be damaged through the placing process–or you can`t pull within the cable,” he explains.
Due to limited volume of tensile pull that one could exert in the cable, people search for approaches to decrease the coefficient of friction in the conduit. “There are actually products on the market like prelubricated conduit,” says Stewart. “And there`s even a different technology being utilized for placing cable, called air-blown fiber (or ABF), the location where the fiber-optic cable is blown to the conduit. We manufacture whatever we call the `air-trak` system–a conduit system with chambers–for use in ABF installations.” [Air-blown fiber can be obtained in the states from Sumitomo Electric Lightwave Corp. (Research Triangle Park, NC).]
Conduit and innerduct have one important thing 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 number of cables grows to fill every one of the space within the conduit. Therefore, selecting the correct trade size is important, simply because you must leave sufficient clearance involving the walls of the conduit and other cables (start to see the eia/tia-569 standard). Typically, conduit trade sizes vary from 1/2 to 6 inches in diameter. Minimum conduit size suggested for backbone cables is 4 inches. Sufficient clearance must be available to allow pulling the cable without excessive friction or bending.
The NEC conduit-fill tables define the quantity (being a percentage) of several types 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 with regards to data cables in conduit. The genuine question for data cable is: Is it possible to pull it into the actual size of duct that you`ve selected?”
“The main decision when installing conduit is the dimensions of the conduit and clearance through the wall,” says Clawson. For external use, we use 4-inch PVC conduit, so we attempt to install just as much conduit within the trenches as we can for future use.”
Cables are continually included in 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 within the conduit. A good way to provide for future changes is always to subdivide larger conduits with innerducts, which are smaller in diameter than conduit, generally nonmetallic, and semiflexible.
“Inside an existing structure, many installers usually do not wish to pull new cable across the cable already in the conduit,” says Stewart, “mainly because they risk damaging the current cable. To optimize a larger 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 utilized for future cable placement.”
Innerducts are classified by outside diameter (OD) whereas trade-size conduits use inside diameter (ID). One-inch innerduct is usually used within buildings; however, 11/4-, 11/2-, and two-inch innerducts are available for larger fiber cables. Although innerducts take up space within a conduit, they supply 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, then one spare. What you wish to do is pull all the dexlpky51 you may at installation time.”
Typically created 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 as well as the physical properties in the inner wall in 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 really is typically useful 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 the cable jacket is “lifted” clear of and contains a reduced region of connection with the pipe, reducing the coefficient of friction. However the general guideline is: the larger the hole, the simpler it`s going to be to drag the cable,” he says.
According to Clawson, “We use ribbed innerduct if we`re pulling one innerduct, because it`s much easier to handle. If we`re pulling via a directional boring machine and it`s a multiple pull, we use smooth innerduct. It is much easier to pull smooth innerduct on the top of an easy surface, and yes it doesn`t kink as easily as ribbed innerduct.”
When utilizing innerduct, it is important to verify whether it be a plenum or non-plenum area and to install the innerduct together with the appropriate support. When the innerduct is secured with tie wraps within a plenum area, always employ plenum-rated products.
Innerduct is usually offered in a single color–orange for that fiber-optic communications industry. Color is often installation-specific; by way of example, one color for data cable, one for telephone, and so forth. “There is a movement afoot in order to use color designations for various applications,” says Stewart. “Orange is generally communications, red would be for electrical power, and yellow for gas.”