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.
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.