Electrical Duct Bank Artical 310

[nmadhusudhan8@gmail.com]

Hi Everyone,

What is the de-rating factor if i have 10 electrical ducts in a Duct bank.

Thank you,
Madhu

 

[erickench]

You mean 10 electrical cables in a single duct? It would be 50%.

 

[don_resqcapt19]

Take a look at the information in Annex B, but I don't think that there is a table for 10 ducts. There can be issues with excessive heat in duct banks and that will result in a lower ampacity than normal. Often engineering software is used for these calculations and you have to know something about the thermal resistivity of the backfill around the ducts.

 

[charlie b]

Let me add that if you do find a Table that is appropriate for the underground ductbank configuration that you plan to use (and there is no such Table for 10 ducts), then the ampacity values you take from that Table does not constitute a "derating." You are looking up an ampacity. You are not taking one value of ampacity, and multiplying it by a derating factor, in order to get a final ampacity value.