In outside-plant installations, conduit is generally installed underground to guard cables from damage as well as facilitate cable placement for immediate and future needs. You can even install Conduit Fittings Wholesale inside buildings to facilitate pulling cable between two points such as in the telecommunications closet (TC) to function-area outlets, or from an equipment room to a 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 through which cables could be pulled. Furthermore, although conduit can be used to house various kinds of cable, the National Electrical Code (NEC) uses the word “optical fiber raceway” in Article 770 to clarify conduit, or raceways, for optical-fiber cable. Various kinds of conduit can be found, 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 injury to 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 can be obtained on reels in longer, continuous lengths which do not have to be joined as much.
“The only issue with installing EMT conduit is that it demands a special skill set and training, together with plenty 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 have to do any nonstandard bends yourself, and that`s where 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 a building, several types of duct are being used–as an example, riser- and plenum-rated–but all our products are manufactured from thermoplastic materials, such as polyvinylide fluoride [pvdf] and polyvinyl chloride [pvc]. The thermoplastic materials are easier to install than metal.”
You will find 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 necessarily rated. Then there`s a riser product, rated by Underwriters Laboratories [UL], that is generally a thermoplastic material for example polyethylene or PVC with fire-retardant chemicals included with it. Along with the third sort of duct is UL plenum-rated, generally a pvdf product, which 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 that conduit and innerduct manufacturers make is perfect for outside plant. Some manufacturers offer prelubricated innerduct and conduit, “very often incorporating some form of silicon,” he says. “For premises cabling, Pyramid supplies a plenum raceway (tested to UL-910) along with a riser raceway (UL-1666) for installation in vertical shafts.” Furthermore, the riser product is halogen-free and is also often used for military, shipboard, or tunnel applications, based on the specifications.
Naturally contractors install conduit where building codes require it, and also the location where the cabling system needs physical protection or defense against unauthorized access.
“We use conduit in riser and backbone systems from your building entrance on 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, especially in university campuses. Inside the living quarters, we install cable in conduit as it affords the cable extra protection, and hopefully, keeps it out of students` reach,” he says.
Some cabling contractors would rather have other trades install conduit; for instance, electricians who definitely have more experience with performing this. “Generally, the only real time we use Plastic Flexible Conduit occurs when we`re developing a riser or penetrating a fire wall,” says Smith. “Typically, we may not install conduit from your wiring closet for the workstation outlet. For short distances, as much as 100 feet, we may install conduit between buildings dependant upon the existing infrastructure.
In addition to the traditional smooth-bore type, innerduct can be obtained having a ribbed inner wall to lower friction between the cable sheath and the innerduct wall. “A wave-rib on the inside of the duct reduces surface contact between the cable along with the wall of the duct, thus reducing the coefficient of friction and allowing you to pull cable over longer distances,” says Stewart.
Another variation may be the multicelled conduit system, that 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 stock to work with on other jobs,” he says. “But pre-installed conduit is actually a special application, so overages and underages are sort of costly to cope with.”
For premises applications, Dura-line (Knoxville, TN) has designed a conduit, referred to as Hex-line, for multiple-duct applications between buildings. “As you pull the ducts from the reel (two to each reel), they go into a collector, which Dura-line supplies cost-free,” says Ray McLeary, v . p . of sales. “Each duct carries a female and male part, that are snapped together, making a multiple duct system. This saves time, space, and funds, but the most significant savings is space.” He explains: “Normally, you are able to put three 1-inch innerducts into a 4-inch conduit. With this particular system, you can fit four 11/4-inch or six 1-inch innerducts in to the conduit.”
When selecting 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 gonna pull it spanning a great distance, select a wall thickness that allows 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 else you can`t pull inside the cable,” he explains.
Because of the limited level of tensile pull that you can exert around the cable, people seek out strategies to decrease the coefficient of friction in the conduit. “You can find products in the marketplace 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 fiber-optic cable is blown in 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 usa from Sumitomo Electric Lightwave Corp. (Research Triangle Park, NC).]
Conduit and innerduct have something in common: They facilitate pulling or replacing a cable for added capacity within a premises cabling system. However, every contractor recognizes that as an installation grows, the volume of cables grows to fill every one of the space inside the conduit. Therefore, picking out the correct trade dimensions are important, since you must leave sufficient clearance in between the walls of the conduit as well as other cables (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 should be offered to allow pulling the cable without excessive friction or bending.
The NEC conduit-fill tables define the exact amount (as a percentage) of several types of cable you can use within a conduit. “The NEC typically covers power cables,” says Stewart. “Rich in-voltage cables, you must consider temperature and impedance, which really don`t apply in the case of data cables in conduit. The real question for data cable is: Could you pull it into the actual size of duct that you`ve selected?”
“The main 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, so we attempt to install as much conduit in the trenches as we can for future use.”
Cables are continually included with conduit systems which can be often filled to capacity with generations of older cable. When new cables are added, friction and pulling tension can harm existing cables inside the conduit. A good way to offer future changes is always to subdivide larger conduits with innerducts, that are smaller in diameter than conduit, generally nonmetallic, and semiflexible.
“Within an existing structure, many installers will not desire to pull new cable over the cable already inside the conduit,” says Stewart, “mainly because they risk damaging the present cable. To optimize a more substantial conduit, they`ll install several smaller innerducts inside it. They`ll pull a reduced fiber cable into one of 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 usually used within buildings; however, 11/4-, 11/2-, and 2-inch innerducts are accessible 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 wind up putting in three 1-inch innerducts: one for fiber, one for data, then one spare. What you want to do is pull all the dexlpky51 you can at installation time.”
Typically produced from thermoplastic materials, innerduct comes with 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 along with the physical properties from the inner wall of 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 manufactured from high-density polyethylene, it really is typically used 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 that the cable jacket is “lifted” clear of and possesses a reduced region of contact with the pipe, reducing the coefficient of friction. However the rule of thumb is: the larger the hole, the better it`s likely to be to pull the cable,” he says.
Based on Clawson, “We use ribbed innerduct if we`re pulling one innerduct, because it`s much easier to handle. If we`re pulling by way of a directional boring machine and it`s a multiple pull, then we use smooth innerduct. It can be easier to pull smooth innerduct on the top of a smooth surface, and it doesn`t kink as easily as ribbed innerduct.”
When using innerduct, it is important to verify whether it be a plenum or non-plenum area and also to install the innerduct together with the appropriate support. In the event the innerduct is secured with tie wraps within a plenum area, always use plenum-rated products.
Innerduct is normally offered in a color–orange to the fiber-optic communications industry. Color can often be installation-specific; for instance, one color for data cable, one for telephone, etc. “You will find a movement afoot to attempt to use color designations for various types of applications,” says Stewart. “Orange is normally communications, red can be for power, and yellow for gas.”