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What cable tray is
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What cable tray does
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Where cable tray is used
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How cable tray is constructed
- What cable tray’s features and benefits are
Cable Tray System Overview
Cable tray is simply a “rigid structural system” for cables. In its simplest form, a cable tray is a fabricated “tray” that supports a number of electrical cables. These can be electrical power cables, electrical distribution cables, instrumentation cables, and/or communication cables.
Cable tray is designed to be used in place of conduit pipe. In other words, instead of feeding each electrical cable through a length of metal conduit pipe, the cable is simply laid in a length of cable tray.
Cable tray is usually mounted above the normal operations area. Indoors it is typically suspended from the roof joists or beams. Outdoors it is supported by elevated pipe racks or trestles between buildings or equipment.
Cable Tray System
A typical run of cable tray starts at some type of source, such as a switchboard, and is routed to various termination points throughout the plant. The route it takes normally makes a number of twists and turns. A complete cable tray system, therefore, requires a number of different section configurations including tees, crosses, wyes, and bends, as well straight sections.
Ladder Type Cable Tray
The basic component of any cable tray system is the straight section seen below. This section establishes the TYPE of cable tray that is being used. There are four basic types of cable tray: Ladder, Ventilated Trough, Solid Bottom, and Cable Channel.
The Ladder type is the. most common and widely used, accounting for about 75% of all cable tray sold. One reason is that it is the least expensive design. It also offers maximum ventilation for the cable. The rungs of the “ladder” are welded or swaged to the side rails at spacings of 6, 9, 12, or 18 inches. The support and sag prevention needs of the cable being used determine the rung spacing selection.
VENTILATED THROUGH CABLE TRAY
Below is the Ventilated Trough type cable tray.
This is the second most popular design, capturing about 15% of the market.
In lieu of rungs, a flat or corrugated sheet is used as the bottom tray surface. This allows continuous support for smaller cables while allowing reasonably good ventilation. In some applications, this design is used to prohibit unauthorized access to the cable from beneath the tray.
SOLID BOTTOM CABLE TRAY
The third cable tray design, Solid Bottom, is below. Its share of market is about 10%.
As its name indicates, this cable tray design has a bottom that is completely solid. The bottom material can be either flat or corrugated. Typically, one of a variety of covers is added to provide a completely enclosed tray. When a cover is added, ventilation is quite restricted and the tray really becomes a raceway. Cable fill is also more limited. Solid Bottom cable tray with a cover is often used where access to the cable must be restricted or the cable must be protected from the environment.
CABLE CHANNEL CABLE TRAY
Here is the Cable Channel cable tray design.
This is simply a small U-shaped channel that is available in both solid and ventilated styles. This design is often used as the main tray system for small cables. In other applications, it is used to exit the main cable tray system to the end destination such as a motor control center, enclosure, or piece of equipment.
HORIZONTAL BEND IN CABLE TRAY
Now let’s examine a few of the fittings that are used with straight sections to construct a complete cable tray system. The design of any fitting, of course, must match the design of the associated straight section. For example, if the straight sections being used for an application are the ladder design, then the fittings for that application must be the ladder design also.
Below is a typical horizontal bend for a ladder type system. This particular bend makes a 90° turn. Horizontal bends and vertical bends are also available for 30°, 45°, and 60° turns.
HORIZONTAL TEE OF CABLE TRAY
Here is a typical horizontal tee for a ladder type system. The two turns, one left and one right, are always 90º. When the turns need to be 45º, a horizontal wye is used.
VERTICAL BEND
Finally, a cable tray application may require vertical changes in direction as well as horizontal changes. These changes require vertical fittings.
There are two types: vertical bends and vertical tees. Shown below is a typical 90° vertical bend for a ladder type system. As with horizontal bends, these fittings are also available for 30°, 45°, and 60° vertical bends.
Material Types of Cable Tray
Cable tray is available in four different materials: aluminum, pregalvanized steel, hot-dipped galvanized steel, and stainless steel.
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Aluminum cable tray is the most commonly used because it is the least expensive. This is a good basic material that provides long life with little maintenance.
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The zinc coating of pregalvanized steel is applied at the steel mill before the cable tray is fabricated. This material provides greater strength than aluminum with reasonably good corrosion resistance. Some surfaces are exposed during the fabrication process.
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When greater corrosion resistance is needed, hot-dipped galvanized steel is used. With this material, the zinc coating is applied after the cable tray is fabricated. In this way, all surfaces of the finished cable tray are protected.
- Stainless steel cable tray is used in highly corrosive environments such as is found in some chemical plants. Both Type 304 and Type 316 stainless steel are available.
Advantage of Cable Tray vs Conduit Pipe
Cable Tray vs Conduit Pipe
The primary method of routing electrical cable throughout a building in the United States is conduit pipe. This is not necessarily the best method, it is just “the way it’s always been done.” In Europe, Asia, and Canada, by comparison, cable tray is the predominant method used.
The job of selling cable tray in the United States, therefore, involves two phases. With all customers, we must sell the advantages of cable tray over our competition. With those customers now using conduit pipe, there is also the need to sell the advantages of cable tray over conduit. These advantages are as follows:
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The installed cost of cable tray is less than conduit in most cases. Depending on the size of the installation, the total installed cost of a cable tray system can be up to 60% less than a conduit system.
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Cable tray requires fewer supports than conduit. Supports for cable tray can be up to 20 feet apart. With conduit, depending on size, the distance between supports is only 8 feet. As a result, cable tray requires less support materials and less labor cost.
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Laying cable in cable tray is much easier and faster than pulling cable through conduit pipe. Another saving in labor cost.
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Bolting pre-fabricated cable tray fittings to straight sections requires less on-site labor than bending conduit, resulting in further cost savings.
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There are fewer cable tray sections to handle and install than lengths of conduit for the same installation.
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When rigid conduit is used, both ends of each length must be threaded. Cable tray sections, by comparison, are simply bolted together using splice plates and hardware.
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The entire interior of cable tray can be filled with cable. The fill capacity of conduit, however, is restricted to 40%.
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There is less chance of cable damage when laying cable in cable tray than when pulling cable through conduit pipe.
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A single run of cable tray requires less space than multiple runs of conduit for the same installation.
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The future expansion cost of cable tray is less than conduit. With cable tray, the original design can include space for future expansion. Additional cable is simply laid in the trough as needed. With conduit, any expansion requires the purchase of additional conduit and support material.
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Space requirements are also increased. Because of its open construction, cable tray does not collect moisture or need to be sealed in seal tight environments. The opposite is true of conduit because of its closed construction.
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Cable is readily accessible for maintenance when cable tray is used. With conduit, the pipe must be disassembled to gain access to the cable for maintenance.
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Cable tray requires less design engineering time than conduit.
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Cable tray is safer than conduit.
Features & Their Benefits
Cable Tray is a superior product line. Millions of dollars have been spent on its development. Four years were spent on market research to determine the needs of users and distributors. Three years were spent on product design, manufacturing, engineering documentation, quality procurement, user/designer computer software, technical catalog, application support, and part numbering system. A review of the key product features and benefits follows.
There is a total of over 70,000 individual items in our product line. This includes five different materials, four different overall depths, eight different widths, and a full line of fittings and accessories.
Benefit = one source of supply for all the customer’s cable tray needs
TY-RAP CABLE TIE SLOTS
Exclusive Ty-Rap® cable tie slots 1″ center to center on all ladder ventilated and solid bottoms. Secure cables without kinks and keeps cables uniform.
Cable tie head can be installed inside the tray or outside the tray on the under side. Allows perpendicular attachment of cable instead of conventional skewed attachment.
Benefits = Keeps cable straight and uniform. Eliminates kinking of cable. Reduces cutting pressure of cable tie edges on cable.
FOUR-BOLT SPLICE CONNECTIONS
Snap-in aluminum splice plates for easy installation.
Maximum of four bolts required at each splice to connect two straight sections or connect a fitting to a straight section.
Benefits = Less hardware and less installation time required than conventional connection methods.
OPEN SLOT RUNGS
Underside of each rung equipped with a longitudinal slot that accepts the standard pipe straps used in the Kindorf/Superstrut product line.
Position of rungs are alternated to permit attachment of pipe to underside of tray.
Benefit = Simple attachment of pipe when needed.
FLEXIBLE BARRIER STRIP POSITIONING
Barrier strip attached to tray by bolting through cable tie slots
Allows barrier strip to be positioned laterally in 1” increments. No self-tapping screws used.
Benefit = Position of barrier strip easily customized to need of application.
SNAP-IN SPLICE PLATES
During assembly, each splice plate snaps into position at connection joint.
Benefit = Frees both of installer’s hands to install connection nuts and bolts.
