sgreany
The question you asked has absolutely nothing to do with the ambient temperature.
electricman2 nailed it, there is nothing for the NEC to reevaluate, the rule is a good rule.
First read carefully the name of Table 310.16
Allowable Ampacities of Insulated Conductors Rated 0 Through 2000 Volts, 60°C Through 90°C (140°F Through 194°F), Not More Than Three Current-Carrying Conductors in Raceway, Cable, or Earth (Directly Buried), Based on Ambient Temperature of 30°C (86°F)
The rating of 8 awg in the 75 C column is 50 amps.
Now if the ambient temperature is 30 C as the table is designed around and if the cable or raceway has three 8 AWGs each loaded to 50 amps the temperature of the conductors will approach 75 C.
75 C is 167 F and yes that is warm but it is within the design limitations of any 75 C insulation.
Connect this conductor that is close to 75 C to a 60 C rated breaker and the heat transfer from the conductors to the breaker is very likely to cause the breakers thermal overload to trip the breaker.
Bob
