250.66(A) specifically gives a max size for aluminum but 250.66(B) does not list aluminum at all? Seems odd if aluminum is acceptable why it would not be included in A but not B.
Ok...I get touchy with those words "maximum".....lol
being "not required" to be larger than those sizes is not the "Max Size" possible, just not required to be larger, but could indeed be larger if the designer so chooses. Clearly the maximum size is going to be dependent on your termination and the Engineers imagination. Now I will explain my opinion (for what it's worth)on the oddness of (B)...
1) the 2014 NEC change to Section 250.68(C)(3) to make it clear that the rebar could extend beyond the actual UFER (CEE) location as defined in 250.52(A)(3) and probably more of an issue that no one proposed a change to 250.66(B) to correlate with this change and permit AL to serve this purpose as permitted in 250.62. Typically the method of termination for the (UFER) would indeed bring 250.64(A) into play and limit the application anyway which is why it probably was not added to 250.66(B)....which in light of the changes to 250.68(C)(3) could use some tweaking in the 2020 process....bring on the 2020 NEC....)
I am more than sure a public input will be made during the 2020 cycle...by a future CMP 5 member.....