Cable trays were introduced in the United States in the 1940s as a kind of shield and support for power cables. Yet, despite their long-term use, they are nowhere near as popular here as they are in Europe, where they are the dominant system for running wires (and where conduit is largely not used).
What do those European electrical contractors know that many of their American counterparts don't? According to the manufacturers, using cable trays can yield greater productivity during installation, minimize stress on cables both during installation and subsequent operation, improve aesthetics (in an open ceiling design, for example), simplify maintenance, and provide easy opportunity for upgrading, reconfiguring, and relocating cable as facility needs change. Plus, installers may be able to use smaller-size wiring because heat may be much more easily dissipated in an open tray than in enclosed conduit.
Accommodating outdoor and indoor applications (overhead, open space, perimeter, or underfloor) as well as varied loading depth and load/span requirements, a broad array of cable tray types is available, fabricated in various materials, including steel, stainless steel, fiberglass, and aluminum. Aluminum is the most popular material, because it is light and easy to handle. The most common finishes for steel in cable trays are mill galvanized or hot dipped galvanized after fabrication. Some manufacturers also coat plain steel, galvanized steel, or aluminum with PVC.
Generally, applications that require support for large, rigid cables or other heavy loads use ladder trays (the most popular two-sided rail style), which permit easy drop out, and are the most common choice for power, overall.
Solid-bottom or punched-bottom (ventilated) trough cable trays are other types of two-sided rail cable trays that provide both continuous support and a combination of good ventilation, support, and a high level of protection for heat- generating cables. Wire basket cable trays, used frequently for voice/data and other low-voltage applications, are another option for power applications. They provide cable support, ease of installation, and good ventilation. Various fittings accommodate changes of direction and provide flexibility for different types of cable.
While open trays can help dissipate heat because the wires are not confined as they would be in conduit, steel or aluminum covers (usually available as options) can shelter an installation where additional isolated physical protection is required or specified. Two examples: cable tray passing through floors should be covered for six feet, and cable tray under open walkways should be covered to protect cable from dropped foreign objects. In general, though often specified by those with a conduit mind set, covers are often not needed.
With respect to satisfying strength requirements, specifiers need to consider both the load the system will carry and the span between supports. Systems that use a single center support rather than a two-fastener per location trapeze-style support theoretically would install faster.
Specifiers need also to consider the application environment. For instance, if the installation is outdoors, will the selected support system be able to withstand weathering, wind, and ice and snow loads? Another consideration is whether the system, as fabricated, will hold up in a highly corrosive environment, if that is the intended location.
Ladder cable trays-with two longitudinal side rails connected by individual transverse members-are often used to support heavy-duty power distribution. Cables are pulled (frequently with rollers, sheaves, and pulleys), rather than laid into place. In selecting a ladder tray, specifiers need to determine optimum rung spacing of the straight sections to properly support the cable. While there is no standard, 9-inch rung spacing is the most widely used in the United States. Though wider rung spacings are more economical, they can affect system strength. In addition, rung and side rail attachment methods differ among manufacturers. Flat broad cable bearing rungs, which offer maximized point-to-point contact and support, are offered by most companies. Round or narrow rungs are also often available. In general, in cable installations, ladder cable tray can save appreciably on space compared to conduit.
B-Line Systems, Inc.'s Redi-Rail two-sided rail aluminum cable tray system, featuring I-beam-shaped rungs with a high strength-to-weight ratio, has several user-friendly installation features. These include screw-in/screw-out rungs (tested to 3,000 lb. Pull-apart pressure) and continuously prepunched side rails, which serve as splice connection holes during field cutting.
The prepunched side rails also serve as attachment locations for hanger rod clamps (in place of trapeze supports) and as attachment points for bonding jumpers, branch cable tray systems, and other items. Flex Mount, a new type of splice that does not require bonding jumpers, offers 90 degrees horizontal adjustment and up to 15 degrees vertical adjustment.
The product is available in 2-, 3-, 4-, 5-, and 6-inch depths and seven widths ranging from six to 36 inches. To help facilitate post-installation cable fill depth expansion, the system has incorporated Rail Risers, side rail extensions that accommodate an additional 2-inch depth, says the company.
MP Husky Corp.'s Electray, suitable for multiple large cables such as those typically used in paper mills, power plants, and industrial construction, incorporates flat, broad rungs and a proprietary Thru-Weld technology that completely welds rungs to the outside of the rails for added structural integrity and reduced side rail rotation. The outside weld eliminates inside sharp edges that could damage conductors. An outside flange on both side rails helps preclude snagged wires during installation. The product is available with nine-, 12-, and 18-inch rung spacings and load depths of three to five inches.
Chalfant's ladder-style cable trays use innovative splice plate fasteners that can be finger-spun to within half a turn of being tight. According to the company, the total time to insert the new round-head truss bolts with serrated bottoms and hex nuts with serrated flanges is up to 50 percent faster than traditional-style bolts with serrated necks, which could result in significant labor cost savings both during installation and for later access. The cable trays are available in 12- and 24-foot lengths in widths from six to 42 inches, and with six-, nine-, 12- and 18-inch rung spacing, in a variety of standard finishes. Solid trough (supported on a tray with 12-inch-spaced rung), expanded metal trough, and ventilated trough ladder trays with six-, nine-, and 12-inch rung spacing are available, as well. Chalfant also offers an integral hinged cover tray system that feature built-in half turn spring latches, in both 4- and 6-inch heights.
T.J. Cope offers modular, metallic ladder trays sporting tubular rungs that connect to the side rails by use of a cold swaging process, rather than by welding. Welding typically lowers the strength properties of the base metal, whereas the cold working of the swaging process strengthens the joint, contends the manufacturer. The tubular rungs also feature a flattened cable-bearing surface to eliminate obstructions while pulling cable.
Trough-style ladder cable trays
Trough style cable trays feature solid bottoms, ventilated or louvered bottoms, or punched out bottoms. The trays, which may be hung by two-rod trapeze, or direct from the side rail with clamps, shelf brackets or a center rod, may or may not have internal dividers and covers. They are typically available in galvanized steel, aluminum, and stainless steel, in a variety of finishes and depths.
Chalfant's Series 6 Trough Tray, features one-piece design trays with continuous-run rolled outboard flanges along side rails that protect cable or wire during loading and facilitate smooth loading of cable into the tray. The product, which can be painted or coated with PVC or fusion-bonded epoxy, can be custom modified to special widths and load depths from two to eight inches. The three-inch louvered opening permits easy dropout of cables anywhere along the tray path.
A single center support option allows cable to be loaded from either side. According to the company, the trays take up to 25 percent less space than conduit and cost 40 to 50 percent less to install than conduit. Another mounting option that could save space in cramped above-drop-ceiling installations features two threaded rods and hanger rod clamps that directly attach to the tray side rails. The clamp, by design, gets tighter when loaded, notes the company. Other mounting choices include strut style or shelf wall brackets, trapeze with strut supports, and pedestal splice plates for mounting trays to the floor, vertically up walls, or off floors (elevated up to 10 inches).
In addition to being used as a cable distribution system, GS Metals' Globetray trough cable trays are acting in a starring, rather than supporting, role as decorative custom light enclosures at a new megamall in West Nyack, N.Y., completed in 1998. Designers selected the company's trough-style cable tray, in shiny stainless steel finish, to complement the intended industrial look of the interior of the Palisades Center, which features exposed structural components, air conditioning systems, and water pipes. Lighting for the facility's public areas and entrances comes from standard-colored fluorescent tube lights encased by pieces of the trough style cable tray purposefully suspended at various angles and spacings to create interesting designs, such as the five-point star that decorates the common area near the mall's ice skating rink.
SpecMate enclosed cable tray from The Wiremold Company can be specified with ventilated louvers that facilitate cooling by natural convection while keeping conductors enclosed and protected. Cable tray can be mounted to walls or support columns, providing enhanced protection for cables that are dropped down from horizontal trays.
Center spine/center rail
Center-spine cable trays feature a single central support from which a series of open-ended rungs emanate. This configuration offers a direct, easy method of laying in cable from one or two sides, rather than the threading and pulling method required with trapeze support cable trays, cutting installation time up to 50 percent. Further time may be saved because the trays typically use 50 percent fewer hanging and joining materials.
The Wiremold Company's SpecMate wall-mounted cable trays feature a spine that attaches to the wall and screw-in rungs (on only one side of the spine) that can be removed to avoid obstructions or replaced with longer rungs for capacity expansion. For added flexibility, including additional capacity and separate channels, second and third tiers of rungs can be added when the spine is specified with the appropriate number of factory-punched openings.
Well-suited to building environments where the center of a hallway or room is already packed with lighting, HVAC, sprinkler system, and fire alarm systems, wall-mounted cable trays can be installed feasibly by one man with convenient, secure wall-mounting hardware, says the company. One-inch rungs, which are fitted with plastic caps to prevent injury to the installer and damage to the cables, minimize potential microbending of sensitive cables over time. A variety of color options are available so installers can identify different cable runs. Both screw-down and hinged covers are available.
Mono-Systems, the company that originated the concept of center- hung cable tray back in 1967, offers Mono-Tray center hung cable tray in a broad array of load classes, materials, and styles, including a top-rung design that offers a large-capacity single compartment and a bottom-rung design that divides the tray into two equal compartments, both available in either aluminum or steel.
The Mono-Tray line also includes bottom-rung aluminum removable rung and top-rung aluminum removable rung cable trays. The rungs on the aluminum trays sport a box beam design for additional strength. End caps are available for all trays.
The company also makes stackable Versa-Tier within the Mono-Tray line, as well as bottom-rung dual-rail style cable trays, in aluminum and steel, with the spines dividing the tray into three separate compartments.
B-Line System's Cent-R-Rail Systems feature Half-Rack and Multi-Tier Half-Rack, (either supported on a wall or on another structure), and ceiling-hung Verti-Rack (featuring multiple tray runs with one center rail), which are well-suited to narrow spaces, as well as ceiling- hung or floor-mounted Data-Track products. Both Multi-Tier Half-Rack and Verti-Rack are expandable after installation via Add-a-rungs. The systems, which feature lightweight, high-strength, corrosion-resistant aluminum, sport a unique Qwik-Bolt splice that reduces the hardware required for connection and can also be used to support the tray.
Facilitating easy system expansion, grid-design universal hub fittings allow installers to connect up to eight trays in random directions. Colored end caps are available for system labeling. Designed to be interactive with B-Line's strut systems, the Cent-R-Rail Systems, which prevent the transmission of smoke or fumes through the center rail (such as could occur with conduit), are interactive with B-Line's strut systems.
P-W Industries, Inc.'s, Centerline cable tray system incorporates a slot in the center rail, adapted from the standard 1 5/8-inch wide strut, that facilitates quick attachment of accessories, including specially designed clamps for attaching extra rungs in the field, and an innovative welding design. Each rung is arc-welded to the center rail in four places, eliminating the possibilities of loose and rattling rungs, or fatigue associated with mechanical or "crimped" rung connections, according to the company. Various configurations are available, including center rails with the slot on the top or the bottom of the tray, and rails with slots on both the top and bottom sides of the tray.
Thomas & Betts Corporation's (T&B) Center-Lok cable tray system, part of the company's OmniLink line of wire management products, is shipped as unassembled modular spine and rung components. The installer can customize cable tray runs on the spot, facilitating easy accommodation of unanticipated obstacles such as HVAC ducts or plumbing piping and other divisions requiring field modifications.
Up to three tiers are possible, accommodating applications calling for separation of wires or cables. As the center spines are marked at three-inch intervals, no measuring may be required. According to the company, one electrician can install the cable trays using a scissors-type hydraulic lift, cutting labor time and cost by up to 30 percent.
Because the components snap together and apart, rung spacing can easily be changed later, as well, during retrofitting or installation expansion. Their innovative Ty-Rap attachment slots allow cables to be separated and organized, as, for example, for separating primary from secondary feeds MP Husky offers Centray, featuring heavy-duty 5/8 x 5/8-inch rungs with chamfered ends that eliminate sharp edges and the need for end caps. (Caps are available in color for cable identification purposes.) The product can be center hung or wall mounted. An innovative dual-width configuration for separation of different types of cables. Hinge connectors give the installer the ability to change directions either vertically or horizontally to avoid obstacles, says the manufacturer.
While wire baskets are widely recognized as a viable alternative to conduit for voice/data/video and other low-voltage applications, they can also be used for power applications. Wide, shallow baskets typically dissipate heat better than narrow, deep baskets holding a stack of wires. For outdoor (exposed) installations, various coat finishes are often available.
The OBO Bettermann System features wire mesh trays, bends, connectors, clamps, and fasteners that install a wrench and bolt cutter. Simple bends and cuts and a minimum of brackets and connectors allow installers to easily turn straight trays into any vertical or horizontal angle, notes the company. Five hardware accessories handle 95 percent of assembly and connecting needs, saving substantially on installation cost.
Made of carbon-welded steel wire and spot welded at all intersections of the two-inch by four-inch grid for added strength, the lightweight cable tray is available in stock in standard 10-foot lengths, two-inch and four-inch depths, and widths of two-inch increments up to 24 inches in electro and hot-dipped galvanized stainless steel and application-specific finishes.
Cablofil Inc.'s EZ Tray wire baskets, constructed of steel wires up to nearly a centimeter in diameter, include several configurations of low-profile trays. The two-inch-deep trays come with a variety of standard support systems and utilize the company's fast assembly system. Installers can bend the anchoring tabs on the wire to securely mount the tray without screws, bolts, or additional tools beyond a screwdriver.
The trays, finished in stainless steel, have been mounted with the bottom surface against the wall, both horizontally and vertically, and wires have been fastened to the rungs in "clean rooms" at food processing facilities. This type of installation, says the company, reduces the amount of exposed surface on which grime and bacteria can accumulate, requiring less steam washing, as well.
Mono-Systems, Inc.'s Mono-Mesh cable tray system, which can be assembled with a bolt cutter and a wrench, uses only a few components to create a wide array of elbows, tees, offsets, risers, and other fittings from standard tray lengths, according to the company. An innovative, patented, radiused dropout, placed on the tray before the wires are dropped, provides a gentle radius bend minimizing potential stress and strain on the wires.
Universal Electric Company's Starline Track Busway is a low amperage (60, 100, 160 or 225 ampere) track busway system that can be easily reconfigured when changing applications and layouts on the work floor. The busway uses a continuous access, continuously energized slotted track that gives users the flexibility of adding turn-n-lock duplex receptacles, fixtures, and power poles or drop cords down to a work area from anywhere along the busway.
Any plug-in device can be added or removed from the system while it is energized. Unlike conduit, where wires are removed before dismantling, Starline Track Busway can be pulled apart and reconfigured for the new work area in total sections. The extruded aluminum track uses solid copper conductors, that are superior to aluminum conductors, the company asserts.
Minerallac Co.'s Cable Guard saddle system is an example of an inexpensive alternative to cable tray, used most often with Cat 5, fiber optic, and other voice/data/video cables. The continuous radius supports the natural curve of the cable and the wide saddle serves to eliminate pressure points that can degrade bandwidth and damage the cables. Easily mounted to beams for horizontal and vertical runs, it comes as an assembled unit of the saddle can be bought separately to retrofit earlier Minerallac saddle systems.
The FELDMANS write on trends and products, including computers and electronic commerce technologies, for the electrical and general contracting fields. Authors of Construction & Computers (McGraw-Hill), they can be reached at firstname.lastname@example.org or at (914) 238-6272.
Companies mentioned in this article include the following:
B-Line Systems, Inc., www.b-line.com, (800) 280-7994
Cablofil Inc., www.cablofil.com, (800) 658-4641
Chalfant Cable Trays, www.chalfantcabletray.com, (216) 521-7922
GS Metals Corporation, www.mphusky.com, (618) 357-5353
Minerallac Company, www.minerallac.com, (877) 286-2200
Mono-Systems, Inc., www.monosystems.com, (914) 934-2075
MP Husky, www.mphusky.com, (800) 277-4810
OBO Bettermann of North America, Inc., www.obo-bettermann.com, (800) 459-7375
P-W Industries, Inc. www.pwtray.com, (215) 364-3807
Thomas & Betts Corporation, www.tnb.com, (800) 888-0211
T.J. Cope www.alliedsupport.com (800) 416-2101
Universal Electric Company, www.uecorp.com, (800) 333-3490
The Wiremold Company, www.wiremold.com, (800) 621-0049