In outside-plant installations, conduit is usually installed underground to guard cables from damage as well as to facilitate cable placement for immediate and future needs. You can even install Conduit Fittings Wholesale inside buildings to facilitate pulling cable between two points like from your telecommunications closet (TC) to work-area outlets, or from an equipment room to some TC. To guard, isolate, and identify the cables, innerduct–also called subduct–can be installed inside existing larger-diameter conduit.
Conduit is described as a rigid or flexible metal or nonmetallic raceway in which cables might be pulled. Additionally, although conduit may be used to house many types 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 can be found, such as electrical metallic tubing (EMT), rigid metal conduit, PVC, fiberglass, and flexible conduit. For premises installations, how-ever, metal flexible conduit is just not recommended due to potential abrasion harm to the cable jacketing.
Metal conduit, which typically will come in 10-foot lengths, is fairly rigid and needs special tooling and accessories to sign up with it. Nonmetallic conduit is accessible on reels in longer, continuous lengths that do not need to be joined as much.
“A possible problem with installing EMT conduit is it needs a special skill set and training, together with lots of practice–or you end up making swing sets,” explains Kevin Smith, project manager at MTS Services (Bedford, NH). “Metal conduit will come in 10-foot lengths so you must do any nonstandard bends manually, and that`s where technician`s special skill is important.”
Arnco Corp. (Elyria, OH) sells innerduct for the cable-TV, telecommunications, and electric utility markets, says Tom Stewart, electrical products sales manager. “In the building, various kinds of duct are employed–for instance, 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 often polyethylene and it`s not necessarily 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 form of duct is UL plenum-rated, generally a pvdf product, that is fire-retardant and smoke-resistant,” says Jensen.
In accordance with 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 kind 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.” In addition, the riser product is halogen-free and is also often useful for military, shipboard, or tunnel applications, depending upon the specifications.
Of course contractors install conduit where building codes require it, but in addition the location where the cabling system needs physical protection or defense against unauthorized access.
“We use conduit in riser and backbone systems from the building entrance towards the main distribution frame,” says Karl Clawson, senior v . p . and partner, Clawson Communications (Greenwood, IN). “And that we also set it up for horizontal cabling, specifically in university campuses. Within 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 that have more experience in performing this task. “Generally, the only time we use Plastic Flexible Conduit happens when we`re constructing a riser or penetrating a fire wall,” says Smith. “Typically, we would not install conduit from your wiring closet to the workstation outlet. For short distances, around 100 feet, we might install conduit between buildings according to the existing infrastructure.
As well as the traditional smooth-bore type, innerduct can be obtained by using a ribbed inner wall to lower friction involving the cable sheath and also the innerduct wall. “A wave-rib on the inside of the duct reduces surface contact in between the cable as well as the wall in the duct, thus lowering the coefficient of friction and allowing you to pull cable over longer distances,” says Stewart.
Another variation is the multicelled conduit system, which offers outerducts with pre-installed innerducts. Clawson states that, simply because of its cost, his company will not use conduit with pre- installed innerduct. “We keep leftover conduit in store to use on other jobs,” he says. “But pre-installed conduit is actually 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, known as Hex-line, for multiple-duct applications between buildings. “While you pull the ducts off of the reel (two to each reel), they enter into a collector, which Dura-line supplies free of cost,” says Ray McLeary, vice president of sales. “Each duct features a male and female part, that happen to be snapped together, creating a multiple duct system. This saves time, space, and money, but the most important savings is space.” He explains: “Normally, you can put three 1-inch innerducts into a 4-inch conduit. Using this type of system, you are able to fit four 11/4-inch or six 1-inch innerducts in the conduit.”
When buying innerduct, you should 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 likely to pull it across a great distance, pick 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 inside the cable,” he explains.
As a result of limited level of tensile pull that you can exert about the cable, people look for ways to reduce the coefficient of friction in the conduit. “You will find products on the market for example prelubricated conduit,” says Stewart. “And there`s also a different technology used for placing cable, known as air-blown fiber (or ABF), the location where the fiber-optic cable is blown into the conduit. We manufacture what we should call the `air-trak` system–a conduit system with chambers–for usage in ABF installations.” [Air-blown fiber is accessible in the states from Sumitomo Electric Lightwave Corp. (Research Triangle Park, NC).]
Conduit and innerduct have a very important factor in common: They facilitate pulling or replacing a cable for added capacity inside a premises cabling system. However, every contractor understands that as an installation grows, the quantity of cables grows to fill every one of the space inside the conduit. Therefore, picking out the correct trade dimension is important, since you must leave sufficient clearance between the walls from the conduit as well as other cables (start to see the eia/tia-569 standard). Typically, conduit trade sizes range between 1/2 to 6 inches in diameter. Minimum conduit size suitable 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 amount (as a percentage) of different types of cable you can utilize within a conduit. “The NEC typically covers power cables,” says Stewart. “With high-voltage cables, you must consider temperature and impedance, which really don`t apply with regards to data cables in conduit. The actual question for data cable is: Could you pull it into the size of duct that you`ve selected?”
“The most significant 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 we try to install just as much conduit from the trenches when we can for future use.”
Cables are continually included with conduit systems which are often filled to capacity with generations of older cable. When new cables are added, friction and pulling tension may damage existing cables inside the conduit. A good way to provide for future changes is always to subdivide larger conduits with innerducts, that 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 within the conduit,” says Stewart, “simply because they risk damaging the existing cable. To optimize a larger conduit, they`ll install several smaller innerducts within it. They`ll pull a reduced fiber cable into one of many innerducts, then have additional ducts to be used 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 around for larger fiber cables. Although innerducts take up space within a conduit, they give additional protection and flexibility in constantly changing cabling installations.
“Generally, if you`re installing a 4-inch conduit,” says Smith, “you`ll wind up setting up three 1-inch innerducts: one for fiber, one for data, and another spare. What you wish to do is pull all the dexlpky51 it is possible to at installation time.”
Typically produced from thermoplastic materials, innerduct includes a pull string already installed. It can be found in ribbed-, corrugated-, and smooth-wall styles. Some types have prelubricated inside walls. These special coatings and the physical properties in 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 constructed from high-density polyethylene, it really is typically employed for short–1000 feet or less–installations.” Smooth wall is utilized for direct-buried, trenching, plowing, aerial, and directional boring applications. “The Flexible Metal Conduit Pipe is the fact that cable jacket is “lifted” from and it has a smaller section of experience of the pipe, reducing the coefficient of friction. But the principle is: the greater the hole, the easier it`s will be to drag the cable,” he says.
In accordance with Clawson, “We use ribbed innerduct if we`re pulling one innerduct, because it`s easier to handle. If we`re pulling via a directional boring machine and it`s a multiple pull, then we use smooth innerduct. It really is simpler to pull smooth innerduct on top of an easy surface, and yes it doesn`t kink as easily as ribbed innerduct.”
When working with innerduct, it is important to verify whether it be a plenum or non-plenum area and also to install the innerduct using the appropriate support. When the innerduct is secured with tie wraps in the plenum area, always use plenum-rated products.
Innerduct is often offered in a single color–orange to the fiber-optic communications industry. Color can sometimes be installation-specific; as an example, one color for data cable, one for telephone, and so on. “There is a movement afoot to try and use color designations for various types of applications,” says Stewart. “Orange is generally communications, red could be for electricity, and yellow for gas.”