electric 101
Member
- Location
- Logansport, Indiana
When calculating the conductor ampacity for underground duct banks is it necessary to use annex B instead of the tables in 310?
Annex B
- Thread starter electric 101
- Start date
- Status
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Annex B is for informational purpose and not part of the code. So IMO you do not use it unless under engineering supervision. Read the first art. in that annex
electric 101
Member
- Location
- Logansport, Indiana
So in the absence of engineering supervision is it permissable to use the tables in 310.16 for underground duct banks?
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
I am not certain but there are Tables such as 310.77 to 310.80 or so that are for above 2000V. Not sure of your application. Hopefully someone else can help. I have meetings to go to and I am not the best at ducts since I never used them.
rcwilson
Senior Member
- Location
- Redmond, WA
My opinion is that it is permissible to use 310.16 (Table 310.15(B16) in 2011 NEC) for underground banks as long as you follow sections 310.15 A (3) and Table 310.15 (B) (2) (a) "Ambient Temperature Correction Factors" and all of the notes to the tables.
The difficulty is picking the correct ambient temperature and adequately accounting for the mutual heating of adjacent conductors. Appendix B tables include those effects.
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