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You are here: Home / New Articles / Understanding cable trays

Understanding cable trays

April 21, 2016 By David Herres 3 Comments

It is increasingly common to see a large amount of data and communication cabling with bandwidth and throughput demands squeezed into a limited area. All of this may require robust air conditioning to control the I2R temperature rise, not to mention clean electric heat and ventilation where precise temperature control is a factor.

The cable tray is a wonderfully efficient tool used to manage all these wires. With a grounded metal barrier along the centerline to separate power wiring and data/communication cabling, a single, large cable tray installation is capable of routing a large amount of wiring. It heads off the possibility of a disorganized mass of conductors that are difficult to trace when changes must be made or faults located.

A point to note is that there is a difference between cable trays and raceways. The NEC says a cable tray system is a unit or assembly of units or sections and associated fittings forming a structural system used to securely fasten or support cables and raceways. That said, raceways generally mount on a wall in a room where power and communications cables are terminated. Cable trays are usually overhead or under raised floors but carry open wiring. They are used to distribute cables from the source to the point of use.

cable tray
Cable Tray in Wall-Penetration Application.

If a facility resides in a single room, it is common practice to install the cable tray so it follows the perimeter of the workspace. (Right angle fittings are readily available.) It is generally mounted high enough so workers can pass underneath without stooping but not so high that it is close enough to the ceiling to limit access. This presupposes a sufficiently high-ceiling construction in the first place.

As the cable tray follows the perimeter of the room, power and data conductors can enter and exit at various locations, thence traveling in the raceway to the points of usage. For raceways terminating at a tray, a listed cable tray clamp or adapter fastens the raceway to the cable tray system.

Cable trays are available in a wide variety of sizes, styles (including ladder, ventilated trough, ventilated channel, solid bottom and similar structures) and materials, metallic or non-metallic. If made of conductive material, the cable tray is one of the permitted types of equipment grounding conductors. Where sections bolt together, paint is supposed to be scraped off and jumper wires installed to ensure ground continuity.

Ladder trays generally get used where there are larger bundles or heavier cables. The ladder cable tray has two side rails connected by cross members, or rungs. The rungs provide convenient anchors for tying down the cables. A trough cable tray is a prefabricated structure consisting of a ventilated bottom with side rails. The ventilated trough cable tray supports cables better than the ladder type, but the additional support is not significant.

Fiber-optic cable installations frequently go with solid-bottom cable trays because the drooping of fiber-optic cables may degrade system performance. However, the main argument for selecting solid-bottom trays is to reduce electromagnetic/radio-frequency interference or for sensitive circuitry.

When the equipment room serves both computer and telecommunications equipment, under-floor cable-tray systems frequently get installed. Single unjacketed conductors and splices are permitted in cable trays. And the NEC says cable tray is permitted for service conductors, feeders, branch circuits, communications circuits, control circuits and signaling circuits. These requirements as well as Uses Permitted and Uses Not Permitted as well as other specifications and construction and installation details are included in NEC Article 392.

Filed Under: New Articles Tagged With: cable tray

Reader Interactions

Comments

  1. emily bennette says

    June 23, 2016 at 10:15 pm

    This is some really good information about cable. I like what you said about how a cable tray can help keep all of your wires together and organized. Do you know how many cables you would need to start using this method? It seems like it would be more helpful if you had a lot.

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  2. Robin says

    December 10, 2016 at 2:48 am

    Hi,
    Glad to see your post….I am very happy to see your informative post which helps me a lot.

    In the electrical wiring of the high-rise building, a Cable Tray System is used to support insulated electric wires, which are used for distribution. It is also used as an alternate to open wiring system for cable management in commercial as well as industrial structures.

    Cable trays are broadly known for its dependability, adaptability, safety, reliability, low maintenance need, easy installation and long operating life. Numerous of its types available in the market to choose from such as electrical, galvanized, ladder, PVC, perforated, mild steel and stainless steel cable tray, etc. This will help you to make your decision easier as per your industry requires.

    Thanks for being sharing….Keep it up

    Log in to Reply

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