ambient temperature correction factors

[Vertex]

I referenced the wrong code in a previous thread. I'll try again.

Do the ambient temperature correction factors in 310.16 apply to 310.15B6?

 

[jumper]

Interesting. It seems not.... I assume I am missing something. Conduit on a roof in resi?

 

[Vertex]

Residential service feeder sizing.

 

[jumper]

Most resi is a direct service drop or a lateral as far as I know. Are you referring to a mast and derating for it?

 

[Vertex]

Yes, a mast.

 

[charlie b]

Do the ambient temperature correction factors in 310.16 apply to 310.15B6?

No. Absolutely not. Table 310.15(B)(6), which became (B)(7) in the 2011 edition, is not an ampacity table, so there is no way to apply any ampacity correction or adjustment factors.

 

[tkb]

I believe so. Add and then multiply by the correction factor.

(c) Conduits Exposed to Sunlight on Rooftops. Where
conductors or cables are installed in conduits exposed to
direct sunlight on or above rooftops, the adjustments shown
in Table 310.15(B)(2)(c) shall be added to the outdoor temperature
to determine the applicable ambient temperature
for application of the correction factors in Table 310.16 and
Table 310.18.
FPN: One source for the average ambient temperatures in
various locations is the ASHRAE Handbook ? Fundamentals.

I looked at the TOC for the ASHRAE Handbook-Fundamentals and don't see where this information would be listed.

Is it in this book?

Table of Contents 2009 ASHRAE Handbook--Fundamentals

PRINCIPLES
1. Psychrometrics
2. Thermodynamics and Refrigeration Cycles
3. Fluid Flow
4. Heat Transfer
5. Two-Phase Flow
6. Mass Transfer
7. Fundamentals of Control
8. Sound and Vibration

INDOOR ENVIRONMENTAL QUALITY
9. Thermal Comfort
10. Indoor Environmental Health
11. Air Contaminants
12. Odors
13. Indoor Environmental Modeling

LOAD AND ENERGY CALCULATIONS
14. Climatic Design Information
15. Fenestration
16. Ventilation and Infiltration
17. Residential Cooling and Heating Load Calculations
18. Nonresidential Cooling and Heating Load Calculations
19. Energy Estimating and Modeling Methods

HVAC DESIGN
20. Space Air Diffusion
21. Duct Design
22. Pipe Sizing
23. Insulation for Mechanical Systems
24. Airflow Around Buildings

BUILDING ENVELOPE
25. Heat, Air, and Moisture Control in Building Assemblies?Fundamentals
26. Heat, Air, and Moisture Control in Building Assemblies?Material Properties
27. Heat, Air, and Moisture Control in Insulated Assemblies?Examples

MATERIALS
28. Combustion and Fuels
29. Refrigerants
30. Thermophysical Properties of Refrigerants
31. Physical Properties of Secondary Coolants (Brines)
32. Sorbents and Desiccants
33. Physical Properties of Materials

GENERAL
34. Energy Resources
35. Sustainability
36. Measurement and Instruments
37. Abbreviations and Symbols
38. Units and Conversions
39. Codes and Standards

 

[charlie b]

If you are dealing with a situation in which the ampacity of a conductor might be altered due to some physical condition (e.g., ambient temperature, sunlit roof, more than three current-carrying conductors in a raceway), then you need to go to table 310.16 for the ampacity values. Table 310.15(B)(6) does not have any ampacity values, so it cannot be the starting point for an ampacity derating process.

 

[Vertex]

Charlie, I interpreted this the same as you. My AHJ used to have an amendment to the NEC that required us to go one gauge larger. That amendment has been dropped, but they interpret the ambient temperature correction factors in 310.16 to apply to 310.15B6 (2008 edition). I wonder if this issue has been addressed in any trade publications. I'd like to give my AHJ a reason to reconsider their interpretation. If their are any inspectors reading this, I would appreciate hearing your opinion on this.