Derating Factor of Cables 1

[mab2008]

In the NEC code, I don't find any reference to "derating factor of 3 phase cables" when bundled / stacked together either underground (directly buried) or above ground thru cable trays? Need some suggestions on this.

 

[resqcapt19]

The cable tray ampacities are covered by the rules in 392.11 and it is my opinion that if you bundle cables in other applications you derate based on the total number of current carrying conductors in all of the cables that are bundled together. Given that the derating factor goes up to 50% when you get to 10 current carrying conductors, the pratical limit would be three 3 phase cables in any one bundle. Also if you are bundling only part of the total length of the cables, you may not be required to derate. See the exception to 310.15(A)(2).

 

[raptor6458]

You derate cables in group installation (bundle) and you also derate cables for various ambient temperature whether it is in ground (buried) or in air (cable trays, etc).