I can't find 310.10 (H)5.
Some multiconductor cables, usually in the larger sizes, will put in three EGC's to reduce the total cross-sectional area of the cable. The combined cross-sectional area of these three EGC's is equivalent to or exceeds the standard 250.122 EGC, i.e. its cross-sectional area.
Thanks, that makes sense . I got hung up on "Sectioned" Equipment.