Derating Factors between multiple service conduit runs

[Luther1]

I am somewhat a novice in using the NEC since I work on the utility side of the service point of delivery. I found derating factors for conductors within the same conduit, but I was unable to readily locate any derating factor(s) for using multiple conduit runs for the service either in air or in earth. Where can I find these multiple conduit derating factor(s) if there is one. Thanks, Luther1

 

[luckylerado]

Each raceway is derated separately as individuals per the rules of 310.15. Additional derating for parallel conductors is not something that NEC requires.

 

[Carultch]

I am somewhat a novice in using the NEC since I work on the utility side of the service point of delivery. I found derating factors for conductors within the same conduit, but I was unable to readily locate any derating factor(s) for using multiple conduit runs for the service either in air or in earth. Where can I find these multiple conduit derating factor(s) if there is one. Thanks, Luther1

Thermally, you can ignore all the other conduits, for ampacity calculation within any given conduit. Derating only applies to wiring within the same conduit or other wiring structure.

 

[GoldDigger]

For really large installations with multiple underground duct banks there are derating factors which are applied depending on the exact geometry of the duct bank. But I do not think that they would necessarily apply to your case.
Take a look at Informative Annex B in the NEC.
The direct application of duct bank corrections in the body of the code is for MV rather than LV wiring. (310.60 [2011])