NEC Table 310.15(B)(16) vs Table B.310.15(B)(2)(7)

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Rai136926

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I have a designer who designed an underground feeder based on Table B.310.15(B)(2)(7) and the DPD is not excepting it. Is there a rule where we can not apply Table B.310.15(B)(2)(7)?

When is appropriate to use Annex B?

thanks
 
Rai136926 said:
I have a designer who designed an underground feeder based on Table B.310.15(B)(2)(7) and the DPD is not excepting it. Is there a rule where we can not apply Table B.310.15(B)(2)(7)?

When is appropriate to use Annex B?

thanks
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I think you mean 310.15(B)(7)???? You can only use that table for feeders in a residence when the feeder carries the entire load of the dwelling. In most cases that is not the case so you must use 310.15(B)(16)



As for annex B
Annex B

This informative annex is not a part of the requirements of
this NFPA document but is included for informational purposes
only.
B.310.15(B)(1) Equation Application Information. This
informative annex provides application information for ampacities
calculated under engineering supervision.
Click to expand...
 
Of course the DPD (Department of Planning and Development) would not approve that! They don't exist anymore, and can't approve anything! :happyno:

Now, if you want to deal with the DCI (Department of Construction and Inspections, the successor to DPD), then I would say that you need to supply more information. What is the nature of the installation? What is the wire type and insulation rating? What is the calculated load? Are you following the installation pattern of the 1-, or 3-, or 6- duct configurations as shown in the details cited in the table? What value of thermal resistivity are you using, and what is your basis for using that value? Are you within the limits described at the top of the table (e.g., three conductors, 75C wire, 20C ambient)? Are they calling for you to provide a drawing that bears a PE seal and signature?

Oh by the way, why would you want to use that table anyway? The ampacity values it gives us are lower than those of 310.15(B)(16).

 
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