Cooper Bussmann CT02MAN manual Construction Specifications. B Smooth Edges

moisture content, however the minimum density that should be used for snow is 5 pounds per cubic foot. The engineer will have to contact the weather service to determine the potential snow falls for the installation area or consult the local building code for a recommended design load.

Usually cable trays are installed within structures such that the structure and equipment shelter the cable trays from the direct impact of high winds. If wind loading is a potential problem, a structural engineer and/or the potential cable tray manufacturer should review the installation for adequacy. To determine the wind speed for proper design consult the Basic Wind Speed Map of the United States in the NESC (Figure 250-2).

For those installations located in earthquake areas, design engineers can obtain behavioral data for B-Line cable trays under horizontal, vertical and longitudinal loading conditions. Testing done for nuclear power plants in the 1970's indicates that cable trays act like large trusses when loaded laterally and are actually stronger than when loaded vertically. Cable tray supports may still need to be seismically braced and designers should consult the B-Line Seismic Restraints Catalog for detailed design information.

The midspan deflection multipliers for all B-Line cable trays are listed in the Cable Tray Systems catalog. Simply pick your support span and multiply your actual load by the deflection multiplier shown for that span. The calculated deflections are for simple beam installations at your specified load capacity. If a deflection requirement will be specified, extra care needs to be taken to ensure that it does not conflict with the load requirement and provides the aesthetics necessary. Keep in mind that continuous beam applications are more common and will decrease the deflection values shown by up to 50%. Also, aluminum cable trays will deflect 3 times more than steel cable trays of the same NEMA class.

To complete the design, the standard straight section length and minimum bend radius must be chosen. When selecting the recommended length of straight sections, be sure that the standard length is greater than or equal to the maximum support span. Choose a fitting radius which will not only meet or exceed the minimum bend radius of the cables but will facilitate cable installation.

[See page 11 for more information on selecting the appropriate cable tray length]

Cooper B-Line, Inc

392.5.Construction Specifications. (B) Smooth Edges.

This is a quality statement for cable tray systems and their construction. B-Line cable tray is designed and manufactured to the highest standards to provide easy, safe installation of both the cable tray and cables.

392.5.Construction Specifications. (C) Corrosion Protection.

Cable tray shall be protected from corrosion per Section 300.6, which lists some minimum criteria for different corrosive environments. The B-Line Cable Tray Catalog contains a corrosion chart for cable tray materials. Cable trays may be obtained in a wide range of materials including aluminum, pregalvanized steel, hot dipped galvanized steel (after fabrication), Type 304 or 316 stainless steel, polyvinyl chloride (PVC) or epoxy coated aluminum or steel and also nonmetallic (fiber reinforced plastic). Check with a metallurgist to determine which metals and coatings are compatible with a particular corrosive environment. B-Line has corrosion information available and may be able to recommend a suitable material. Remember that no material is totally impervious to corrosion. Stainless steel can deteriorate when attacked by certain chemicals and nonmetallic cable trays can deteriorate when attacked by certain solvents.

392.5.Construction Specifications. (D) Side

Rails.

The technical information in Article 392 was originally developed for cable trays with rigid side rails by the 1973 NEC® Technical Subcommittee on Cable Tray. “Equivalent Structural Members” was added later to incorporate new styles of cable tray such as center rail type tray and ‘mesh’ or wire basket tray.

392.5.Construction Specifications. (E)

Fittings.

This section has been misinterpreted to mean that cable tray fittings must be used for all changes in direction and elevation [See Section 392.6(A) Complete system for further explanation). When two cable tray runs cross at different elevations, lacing a cable between the rungs of one tray and dropping into the other is a common practice which changes the direction of the cable while providing adequate cable

Cable Tray Manual

20