The face of cable tray is changing to meet today’s market needs
A few short years ago, cable tray was a “smoke stack” product, used primarily in heavy industrial facilities to support power cables. Today it is still servicing the industrial and power users, but it has also found its way into institutional and commercial applications, supporting telecom cabling systems. The reason for its rapidly changing characteristics is that the products are adapting to changing customer needs.
The electrical and telecom industries have discovered cable tray strengths, safety, speed of installation, openness for future change, adaptability, and today, the vast product selection tailored to particular needs.
Traditional two side rail cable tray
This grouping of product is from the old school. Its primary characteristic is as the product is defined—a support system. In its heaviest form, cable trays are very efficient bridges that can span long distances, up to 30 feet, and carry amazing loads.
These “bridges” can be built from steel, stainless steel, aluminum, and fiberglass. The carbon 0/2 steel can be hot dip galvanized after fabrication or mill galvanized. Each material/finish has its advantages and disadvantages.
Aluminum is the material of choice–excellent corrosion protection, light weight, high strength, no finish to specify or repair, ease of field fabrication, and more economical to install. The environment is the ultimate controller as to the material and/or finish of a system. 316 stainless steel or fiberglass may be required in some corrosive areas.
After the material /finish has been considered, the bottom type of cable tray needs to be determined. Ladder, ventilated trough, solid bottom (trough) are common styles available. Ladder is the most common as it provides the most cable freedom and air circulation (for power cables).
For ladder-type systems, the rung spacing needs to be selected for the straight section. The most common rung spacing (not the standard) in the U.S. is nine inches. With certain exceptions, the rung spacing is controlled by the support requirements of the cables being supported. Longer rung spacings are more economical and provide added cable freedom but can affect the system’s strength.
Ventilated trough systems are for very small cables requiring more support and solid bottom flat floor systems provide a safe resting place for delicate high tech cables that do not generate heat.
The solid bottom metal system with solid metal covers also has applications in environmental air areas supporting non-plenum rated cables.
It’s important to note that a solid bottom, covered cable tray remains a cable tray and is not a wireway (tray-rated cables required).
The next issue is the strength requirement. Remember, these are support systems (bridges), so not only is it important to consider the load but the span (distance between supports) must be known. It is also important to consider other stresses the system must withstand–ice, wind, and snow loads. Needless to say, matching the system strength to the installation requirement is important.
As standard two side rail cable tray systems cover a wide range of sizes, strengths, and styles, so do their applications. The heaviest special systems can span 30 feet and are used when intermediate supports are impossible or impractical (over roadways, for example). The lightest systems are best suited for non-power, indoor installation where the span is from eight to ten feet. The mid-range between these extremes covers a vast amount of applications and can be found from offshore oilrigs to your county courthouse, supporting heavy power cables to fiber optic cables.
The traditional two-side rail cable tray product offering is the core of the domestic cable tray industry. New systems are being developed to satisfy more specific customer needs.
Channel type cable systems are used as a flexible, low-cost means of connecting equipment to main tray runs. Often channel feeds power down to a pump or motor within an industrial facility.
The compact size of channel makes it easier to position around and connect to equipment. This style of cable tray is available non-ventilated or ventilated, as shown in (figure D).
Center supported cable trays
Today, another type of cable tray is available for cable support and management. These systems are manufactured from aluminum and steel, with aluminum again being the material of choice. The advantages of these types of cable tray are installation speed and maximum cable freedom. These systems were generated to allow installers to side fill the cables, eliminating the stresses of pulling cables. They install using a variety of connectors and couplings, as opposed to pre-manufactured fittings. This adds to the installation speed and simplicity. The applications of these systems are primarily to support datacom cabling systems.
The rungs pass through the center spine at the bottom, or through the top.
Both top or bottom mount systems allow the installer to lay cable in from the sides as opposed to pulling cables through trapeze type supports.
As not all installations or customer needs are the same, more specialized systems have developed. Wall-mounted racks are available as well as multi-tiered systems.
Wire basket systems
The newest cable support systems to hit our shores are wire basket systems.
These systems are created from a steel wire two-inch by four-inch mesh. Their strengths are their low profile, unmatched installation adaptability, simplicity of accessories, and distribution stockable characteristics. Of the variety of finishes available, zinc plated is the most commonly used. These systems are not new to the world systems, as they are commonly used in Europe.
The 2×4 wire mesh construction offers some desired advantages not at first visible.
By cutting and removing segments of this system, it can be reformed and changed into “fittings”. Installers will find these wire basket systems the most on-site adaptable of all the systems.
The wire baskets are being used primarily in the telecom sector of the market. As the acceptance increases and as distribution stock becomes more common, these systems can become an important part of the continuing cable tray evolution.
Cable tray today is ever changing, ever growing. It is doing what it should; it is evolving to satisfy a constantly changing set of customer needs. All of these systems have their strengths, all have their weaknesses. They are a growing part of the cable support products today and will continue to adapt and grow.
Standards affecting the two-side rail product groupings are: the applying electrical code, NEMA VE-1 or FG-1, UL classification, and NEMA VE-2. The applying electrical code depends on your area. Should it be the National Electrical Code, Article 318 will be of major interest. This document addresses cable fill allowed for different product types, where it can and can’t be used, and the cable types it can support. The NEMA VE-1 and NEMA FG-1 standards address the manufacturing standards for metal (VE-1) and non-metallic (FG-1) systems. These publications contain the standards to which the National Electrical Manufacturers Association members manufacture their products. The NEMA VE-2 is a fairly new document created to be an installation guide.
At this time, there are no domestic standards that mention wire basket systems. The system’s loading capabilities are being stated in terms that the U.S. standards do not address. The loading is being determined by continuous beam testing, and a specified deflection is the controlling factor. This type of testing is common in Europe and is part of the proposed IEC (International Electrotechnical Commission) cable tray specification.
As the IEC spec will not be completed until sometime in 1999, the testing method being used is hard to define.