This seems to support what was stated above. Now you would have to use the 60C rating as the minimum. This makes sense since the insulation has no affect on the ability of the conductor to carry the fault, at least not enough to be an issue.
Personally I would like to see an exception that reads-- where a raceway is used that can also be used as a grounding means then no increase is necessary. Why does one have to increase the size of the EGC if they are using emt.
Dennis where do you read that you must use the 60C rating. If you are using THHN and both ends support 70C connections then the minimum size for a 50 amp circuit would be #8 and if you used # 6 as proposed by the OP then an upsize EGC would be necessary. This would be a legitimate argument.
Why the Code panel can't move away from this type of nonsense is beyond me. If this rule was intended to add safety for long runs then say so in the rule. Make a minimum distance. Also make a starting point from what size EGC you start the upsize from. Not all cables have the same size EGC as others do for the same size CCC as I found in my reading yesterday.
SER cable seems to have larger EGC than necessary. In my opinion SER already has larger EGC.
What is real intent of the authors of this rule. Are they backed by cable manufactures? Wht is the motivation. The corrected language is absurd. The code making body needs to put down on paper what the mean.
Again in the 2002 hanbook ( I don't know who approves it's interpetation) explains this rule as to be applied to Voltage drop conditions.
This rule is getting more nonsense as the days go by. Hear I am complaining about a rule that if corrected will not help me or affect me for 6 years!
Some would say that is insane!