In outside-plant installations, conduit is generally installed underground to guard cables from damage and to facilitate cable placement for fast and future needs. You may also install Conduit Fittings inside buildings to facilitate pulling cable between two points such as from your telecommunications closet (TC) to be effective-area outlets, or from an equipment room into a TC. To guard, 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 could be pulled. Additionally, although conduit can be used to house many 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. Various kinds of conduit can be purchased, 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 result of potential abrasion problems for the cable jacketing.
Metal conduit, which typically comes in 10-foot lengths, is rather rigid and requires special tooling and accessories to sign up with it. Nonmetallic conduit is accessible on reels in longer, continuous lengths which do not must be joined as often.
“The only issue with installing EMT conduit is it demands a special skill set and training, in addition to plenty of practice–or you end up 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 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. “Inside a building, various kinds of duct are utilized–by way of example, riser- and plenum-rated–but all of our products are produced from thermoplastic materials, for example polyvinylide fluoride [pvdf] and polyvinyl chloride [pvc]. The thermoplastic materials are simpler to install than metal.”
You will find three differing types (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 necessarily rated. Then there`s a riser product, rated by Underwriters Laboratories [UL], which is generally a thermoplastic material for example polyethylene or PVC with fire-retardant chemicals included with it. And also the third form 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 for outside plant. Some manufacturers offer prelubricated innerduct and conduit, “often incorporating some form of silicon,” he says. “For premises cabling, Pyramid delivers a plenum raceway (tested to UL-910) plus a riser raceway (UL-1666) for installation in vertical shafts.” In addition, the riser item is halogen-free which is often used for military, shipboard, or tunnel applications, based upon the specifications.
Obviously contractors install conduit where building codes require it, but also where the cabling system needs physical protection or defense against unauthorized access.
“We use conduit in riser and backbone systems in the building entrance on the main distribution frame,” says Karl Clawson, senior v . p . and partner, Clawson Communications (Greenwood, IN). “And that we also do the installation for horizontal cabling, especially in university campuses. Within the living quarters, we install cable in conduit because it provides the cable extra protection, and hopefully, keeps it of students` reach,” he says.
Some cabling contractors prefer to have other trades install conduit; for instance, electricians who definitely have more experience of performing this. “Generally, really the only time we use Plastic Flexible Conduit happens when we`re developing a riser or penetrating a fire wall,” says Smith. “Typically, we may not install conduit in the wiring closet for the workstation outlet. For brief distances, up to 100 feet, we might install conduit between buildings based on the existing infrastructure.
In addition to the traditional smooth-bore type, innerduct is offered by using a ribbed inner wall to reduce friction between the cable sheath and also the innerduct wall. “A wave-rib on the inside of the duct reduces surface contact between your cable as well as the wall of your duct, thus lowering 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 its cost, his company fails to use conduit with pre- installed innerduct. “We keep leftover conduit in store to make use of on other jobs,” he says. “But pre-installed conduit is actually a special application, so overages and underages are form of costly to cope with.”
For premises applications, Dura-line (Knoxville, TN) has designed a conduit, generally known as Hex-line, for multiple-duct applications between buildings. “As you may pull the ducts off the reel (two to every reel), they get into a collector, which Dura-line supplies free of cost,” says Ray McLeary, v . p . of sales. “Each duct carries a male and female part, which can be snapped together, building a multiple duct system. This saves time, space, and money, but the most significant savings is space.” He explains: “Normally, you are able to put three 1-inch innerducts right into a 4-inch conduit. With this particular system, it is possible to fit four 11/4-inch or six 1-inch innerducts in to the conduit.”
When selecting innerduct, you must also be concerned with its tensile strength and crush resistance. “The thicker the wall material, the larger the tensile rating,” says Stewart. “If you`re planning to pull it across a long distance, decide on a wall thickness that lets you pull the duct over that distance. The crush-resistance feature helps to make certain that the innerduct won`t be damaged throughout the placing process–or else you can`t pull in the cable,” he explains.
Because of the limited level of tensile pull that you can exert in the cable, people look for ways to decrease the coefficient of friction inside of the conduit. “There are products on the market including prelubricated conduit,” says Stewart. “And there`s a different technology getting used for placing cable, generally known as air-blown fiber (or ABF), the location where the fiber-optic cable is blown in 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 america from Sumitomo Electric Lightwave Corp. (Research Triangle Park, NC).]
Conduit and innerduct have something in common: They facilitate pulling or replacing a cable for 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, deciding on the correct trade dimensions are important, as you must leave sufficient clearance between the walls of your conduit and other cables (begin to see the eia/tia-569 standard). Typically, conduit trade sizes cover anything from 1/2 to 6 inches in diameter. Minimum conduit size recommended 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 total amount (as a percentage) of several types of cable you can utilize inside a conduit. “The NEC typically covers power cables,” says Stewart. “Rich in-voltage cables, you need to consider temperature and impedance, which really don`t apply with regards to data cables in conduit. The real question for data cable is: Are you able to pull it into the size 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 as much conduit within the trenches as we can for future use.”
Cables are continually added to conduit systems that 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. A good way to offer future changes is 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 do not would like to pull new cable over the cable already within the conduit,” says Stewart, “because they risk damaging existing cable. To optimize a larger conduit, they`ll install several smaller innerducts inside it. They`ll pull a reduced fiber cable into one of many 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 generally used within buildings; however, 11/4-, 11/2-, and 2-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 end up putting in three 1-inch innerducts: one for fiber, one for data, then one spare. What you want to do is pull as much dexlpky51 you may at installation time.”
Typically manufactured from thermoplastic materials, innerduct features a pull string already installed. It comes in ribbed-, corrugated-, and smooth-wall styles. Some types have prelubricated inside walls. These special coatings and the physical properties from the inner wall in 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 can be typically useful for short–1000 feet or less–installations.” Smooth wall can be used for direct-buried, trenching, plowing, aerial, and directional boring applications. “The Metal Flexible Conduit is the fact that cable jacket is “lifted” clear of and has a lesser part of contact with the pipe, lowering the coefficient of friction. Nevertheless the rule of thumb is: the larger the hole, the better 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 easier to handle. If we`re pulling through a directional boring machine and it`s a multiple pull, we use smooth innerduct. It really is simpler to pull smooth innerduct in addition to an even surface, and yes it doesn`t kink as easily as ribbed innerduct.”
When using innerduct, you should verify whether it be 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 employ plenum-rated products.
Innerduct is generally offered in one color–orange for that fiber-optic communications industry. Color can often be installation-specific; by way of example, one color for data cable, one for telephone, and so on. “There exists a movement afoot to attempt to use color designations for various applications,” says Stewart. “Orange is normally communications, red can be for power, and yellow for gas.”