When using a concrete encased grounding conductor as your main means for grounding, should you size your wire accordingly to 250.66 and treat it as your main GEC?
See 250.66 (B) connections to concrete encased electrodes. this sections modifies table 250.66. There is a difference between table 250.66 and section 250.66
If its the main GEC depends on what other electrodes are available, and how they are connected.