Table 250.102.(C)(1) is a new table for the 2014 NEC. Previously, we were required to use Table 250.66 for sizing the Grounding Electrode Conductor (GEC), Grounded Conductors, and Bonding Jumpers. Now, all Table 250.66 is used for is the Grounding Electrode Conductor. The new table is to be used for the others. The only difference I see is in the last line. Table 250.66 basically says if the Largest Ungrounded SE Conductor (or equivalent parallel area) is over 1,000kcmil, use a minimum size 3/0 Grounding Electrode Conductor.
The new Table 250.102.(C)(1) says if the Largest Ungrounded Conductor (or equivalent parallel area) is over 1,100kcmil then "see the notes." The notes then apply the 12-1/2 percent rule. That is; the Grounded Conductor can be no smaller than 12-1/2 percent of the largest ungrounded supply conductor. So, at 1,100kcmil, a 3/0 is slightly larger than 12-1/2 percent (Chapter 9, Table 8). If I parallel three (3) 500 kcmil conductors then I would have to move up to a 4/0 Grounded Conductor to meet the 12-1/2 percent requirement.
So, why don't we have to upsize the GEC in Table 250.66 beyond a 3/0? Must not this grounding electrode conductor also be able to carry available fault current imposed, even though it is into the earth? Hopefully, someone with some Code theory background can explain this one.