Table B.310.7 Ampacities?

[EEC]

Under most installations we install 4/0 THHN for loads @200Amps, right? But Table B.310.7 in the back of code book says you can install 2/0 thhn if you use three conductors in underground ducts. So does this mean you can use 2/0 thhn if you install 3-2/0 thhn conductors in sch 40 pvc conduit with 18 inch cover?

 

[e57]

Do you have an EE stamp? Then you can use that table, and all the other info in Annex B.

Annex B provides guidance on the use of the general formula for ampacity found in 310.15(C) Engineering Supervision.

 

[bob]

Under most installations we install 4/0 THHN for loads @200Amps, right? But Table B.310.7 in the back of code book says you can install 2/0 thhn if you use three conductors in underground ducts. So does this mean you can use 2/0 thhn if you install 3-2/0 thhn conductors in sch 40 pvc conduit with 18 inch cover?

Keep reading table 310.7. It says at the bottom of the heading that the ducts are arranged as shown in figure B.310.2. Read the notes at the bottom of figure B310.2.