Article 392.9

[jlm]

Article 392.9(A)(3) - My main question has to do with calculating the percentage fill of a cable tray with cables 4/0 and larger and cables smaller than 4/0.

The way that I understand this Article is that if you have a mixer of cable sizes you essentially divide the tray into two areas. All cables 4/0 and larger are in a single layer and all cables smaller than 4/0 can be stacked.

So to find the percentage fill, I have been adding the diameters of all cables 4/0 and larger than multiplying it by 1.2 to change it from a linear dimension to an area fill. Than I add up the cross sectional areas of all cables smaller than 4/0 which gets added to 1.2*(sum of diameters of cables 4/0 and larger). The number I end up with, I consider the area fill for a given tray.

So to find the percentage fill I divide the number I found above by the maximum allowable fill area of a given tray. For example a 24 inch tray has 28 square inches of allowable fill area.

Is this the proper way to size tray? Any help would be much appreciated.

Thanks

 

[steve66]

Re: Article 392.9

I'm not following the 1.2 factor for finding the area of the cable, but otherwise, it sounds right. The relationship between diameter and area is a square one. So you can't just multiply by a single constant to get area.

If possible for your type of cable, I would use Table 5 in chapter 9 to directly get the area.

Steve