Ampacity Rating of ACSR and AAC versus Copper

[Tomm01]

Most bare copper conductors (used in a substation) are rated with an ambient temperature of 40 Deg C and temp rises of 30, 40 and 50 Deg C. All the ACSR and AAC tables I've seen (like Southwire) rate them at 25 Deg C ambient and only a 50 Deg C rise. Why don't the two worlds match their rating basis? How can you get an accurate ACSR or AAC rating at 30 and 40 Deg C rise above 40 Deg C ambient?

Thanks

 

[7anoter4]

There are some manufacturers' catalogues indicating ampacity for AAC and ACSR for 40 oC ambient air. For instance:
In “Aluminum Electrical Conductor Handbook” 3rd Edition published by Aluminum Association, Washington, D. C., 1989

http://www.amazon.com/Aluminum-Electrical-Conductor-Handbook-ECH-56/dp/9991783075

Section II Bare Aluminum Wire and Cable presents a table [Table 3-13] for different cables in 40 oC ambient, no sun and still air or 2ft/sec wind.
You can follow IEEE 738/2006 calculation way also taking into consideration sun exposure and wind. In annex B you'll find even a Basic written program.