In outside-plant installations, conduit is typically installed underground to shield cables from damage and to facilitate cable placement for fast and future needs. You may also install Conduit Fittings Wholesale inside buildings to facilitate pulling cable between two points such as in the telecommunications closet (TC) to be effective-area outlets, or from an equipment room to your TC. To guard, isolate, and identify the cables, innerduct–also called subduct–can be installed inside existing larger-diameter conduit.
Conduit is defined as a rigid or flexible metal or nonmetallic raceway whereby cables could be pulled. Furthermore, although conduit may be used to house various kinds of cable, the National Electrical Code (NEC) uses the phrase “optical fiber raceway” in Article 770 to describe conduit, or raceways, for optical-fiber cable. Various kinds conduit can be found, like electrical metallic tubing (EMT), rigid metal conduit, PVC, fiberglass, and versatile conduit. For premises installations, how-ever, metal flexible conduit is not recommended due to potential abrasion harm to the cable jacketing.
Metal conduit, which typically can be purchased in 10-foot lengths, is fairly rigid and needs special tooling and accessories to sign up with it. Nonmetallic conduit can be obtained on reels in longer, continuous lengths which do not really need to be joined as often.
“The only issue with installing EMT conduit is it takes a special skill set and training, in addition to plenty of practice–or you find yourself making swing sets,” explains Kevin Smith, project manager at MTS Services (Bedford, NH). “Metal conduit will come in 10-foot lengths so you need to 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, several types of duct are being used–by way of example, riser- and plenum-rated–but all of our products are manufactured from thermoplastic materials, like 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 often polyethylene and it`s not necessarily rated. Then there`s a riser product, rated by Underwriters Laboratories [UL], which happens to be generally a thermoplastic material including polyethylene or PVC with fire-retardant chemicals added to it. As well as the third form of duct is UL plenum-rated, generally a pvdf product, which happens to be fire-retardant and smoke-resistant,” says Jensen.
Based on 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, “frequently incorporating some sort of silicon,” he says. “For premises cabling, Pyramid provides a plenum raceway (tested to UL-910) and a riser raceway (UL-1666) for installation in vertical shafts.” Furthermore, the riser item is halogen-free which is often useful for military, shipboard, or tunnel applications, based on the specifications.
Obviously contractors install conduit where building codes require it, but in addition the location where the cabling system needs physical protection or protection from unauthorized access.
“We use conduit in riser and backbone systems through the building entrance for the main distribution frame,” says Karl Clawson, senior vice president and partner, Clawson Communications (Greenwood, IN). “Therefore we also install it for horizontal cabling, specially in university campuses. Inside the living quarters, we install cable in conduit mainly because it gives the cable extra protection, and hopefully, keeps it of students` reach,” he says.
Some cabling contractors would rather have other trades install conduit; for instance, electricians who definitely have more experience in performing this task. “Generally, the only real time we use Flexible Plastic Conduit for Cables takes place when we`re creating a riser or penetrating a fire wall,” says Smith. “Typically, we may not install conduit through the wiring closet for the workstation outlet. In short distances, just as much as 100 feet, we may install conduit between buildings according to the existing infrastructure.
In addition to the traditional smooth-bore type, innerduct is available with a ribbed inner wall to lower friction between your cable sheath and the innerduct wall. “A wave-rib within the duct reduces surface contact involving the 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 the multicelled conduit system, that provides outerducts with pre-installed innerducts. Clawson states that, due to the cost, his company does not use conduit with pre- installed innerduct. “We keep leftover conduit in stock to make use of on other jobs,” he says. “But pre-installed conduit is a special application, so overages and underages are type of costly to handle.”
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 from the reel (two to every reel), they go into a collector, which Dura-line supplies free of cost,” says Ray McLeary, vice president of sales. “Each duct has a male and female part, which are snapped together, making a multiple duct system. This saves time, space, and money, but the most important savings is space.” He explains: “Normally, you are able to put three 1-inch innerducts in to a 4-inch conduit. With this particular system, you may fit four 11/4-inch or six 1-inch innerducts into the conduit.”
When purchasing innerduct, you should also be concerned with its tensile strength and crush resistance. “The thicker the wall material, the greater the tensile rating,” says Stewart. “If you`re gonna pull it across a long-distance, select a wall thickness that lets you 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 inside the cable,” he explains.
Due to the limited level of tensile pull that you can exert about the cable, people seek out ways to minimize the coefficient of friction inside of the conduit. “You will find products out there for example prelubricated conduit,” says Stewart. “And there`s a different technology being used for placing cable, known as air-blown fiber (or ABF), where the fiber-optic cable is blown to the conduit. We manufacture everything we call the `air-trak` system–a conduit system with chambers–to be used in ABF installations.” [Air-blown fiber is accessible in america 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 added capacity inside a premises cabling system. However, every contractor recognizes that as being an installation grows, the amount of cables grows to fill all the space in the conduit. Therefore, deciding on the correct trade size is important, as you must leave sufficient clearance between the walls in 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 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 total amount (like a percentage) of different types of cable you should use in the conduit. “The NEC typically covers power cables,” says Stewart. “With high-voltage cables, you have 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 crucial decision when installing conduit is the size of the conduit and clearance from your wall,” says Clawson. For external use, we use 4-inch PVC conduit, and that we try and install as much conduit in the trenches when 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 the conduit. One way to look after future changes is to subdivide larger conduits with innerducts, which are smaller in diameter than conduit, generally nonmetallic, and semiflexible.
“In an existing structure, many installers usually do not would like to pull new cable on the cable already from the conduit,” says Stewart, “since they risk damaging the present cable. To optimize a greater conduit, they`ll install several smaller innerducts inside it. They`ll pull a lesser fiber cable into one of several innerducts, after which have additional ducts to 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 accessible for larger fiber cables. Although innerducts use up space in a conduit, they provide additional protection and adaptability 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 want to do is pull as much dexlpky51 it is possible to at installation time.”
Typically produced from thermoplastic materials, innerduct comes with a pull string already installed. It comes in ribbed-, corrugated-, and smooth-wall styles. Some types have prelubricated inside walls. These special coatings as well as the physical properties of the inner wall in the innerduct ensure less friction and tension when pulling cable.
“Corrugated innerduct is commonly used in plenum and riser products,” says D`Errico. “And, when manufactured 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 fact that cable jacket is “lifted” far from and has a smaller section of contact with the pipe, reducing the coefficient of friction. Although the guideline is: the larger the hole, the simpler it`s going to be to tug the cable,” he says.
According to 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 much easier to pull smooth innerduct on top of a smooth surface, and it also doesn`t kink as easily as ribbed innerduct.”
When you use innerduct, you should verify be it a plenum or non-plenum area and to install the innerduct using the appropriate support. If the innerduct is secured with tie wraps in a plenum area, always use plenum-rated products.
Innerduct is often offered in just one color–orange for your fiber-optic communications industry. Color is often installation-specific; by way of example, one color for data cable, one for telephone, etc. “There is a movement afoot in order to use color designations for various types of applications,” says Stewart. “Orange is normally communications, red will be for power, and yellow for gas.”