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Cable Trays

ORDERING GUIDE

Load/Span Class

Loading and span factors are very important when specifying cable trays. They are essential if one is to choose the most economical tray system that fits ones needs. Referred to as the NEC (National Electric Codes) and NEMA (National Electric Manufacturers Association) this designation defines the load carrying capability and the support span distances for a cable tray system. They are described in NEC & NEMA as shown in the following table.

Schedule of Permissible Loads
Unsupported Free Span

W mm Size mm H mm 600mm 1200mm 1800mm 2500mm
100 1.6 50 1430 355 156 87
150 1.6 50 1458 362 159 88
255 1.6 50 1498 371 160 89.4
300 1.6 50 1540 380 162 91.3
375 2 50 1955 483 210 116.7
450 2 50 1958 483 210 110.7
600 2 50 1964 481 208 110.4
300 2 62.5 2680 664 290 161
375 2 62.5 2685 664 290 161.3
450 2 62.5 2689 664 289 158.9
600 2 62.5 2698 664 289 157.1
750 2 62.5 2707 666 287 155.7
900 2 62.5 2716 667 287 153.7
600 2 75 3491 861 377 206.5
750 2 75 3513 868 377 205.02
900 2 75 3535 874 378 205.02
*All figures given represent the maximum permissible uniformly distributed load in kgs. per running meter.

Load depth

The distance from the top of the cable supporting member (rung or bottom ribs) to the top of the side rail is called the load depth or inside depth. This is normally 75mm, 100mm, 125mm or 150mm and is determined by the size of the cable to be installed.

Fittings Radii

This figure represents the nominal and bend radius of the fittings inner corner. One choice is usually governed by the minimum allowable bending radius of the cables to be installed in the tray. Occasionally 1200mm radius fittings are required. Standard radii for cable tray fittings are 300mm, 450mm, 600mm & 900mm.


GUIDELINES:

Metals Used

Determining what metal and finish to use mainly depends on the environment the tray will be used in.

Steel--Hot Dip Galvanized After Fabrication : Used primarily for outdoor applications. After the tray is made it is dipped into a molten zinc bath so that all surfaces are thoroughly coated. This provides excellent protection from the elements at an economical cost.

Steel--Mill Galvanized : Not generally recommended for outdoor use. Gives excellent service in dry or controlled atmospheres.

Steel--Stainless : Inherently corrosion resistant. Expensive.

Aluminium : All alloys are copper-free. Inherently corrosion resistant. Light weight. Can be used indoors and outdoors.

Rung spacing

If one is using a ladder tray, the rung spacing should correspond to the nature of the cables to be installed in the tray. Standard spacings are 150mm, 225mm, 300mm & 450mm. Small control cables generally call for 150mm rung spacing to prevent cable sag. Very large diameter cable such as interlocked armored cable can use 450mm rung spacing. The most commonly specified spacing is 225mm.

With a trough system one can choose between closely set rungs (no more than 100mm between rungs) or a ventilated, corrugated one piece bottom.

Tray width

Standard cable tray widths are 150mm, 225mm, 300mm, 450mm, 600mm & 900mm. This is the nominal inside width of the tray that is available for cable fill.

 

 

 
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