I am installing a three phase transformer with a 480 primary and 208 secondary. The 480 feed is a sub panel. Can I connect the neutral for the 208 XO buss to the neutral in the 480 sub panel or must I run a new EGC from the XO buss to the system grounding electrode? The 480V panel is also used for flourescent lighting and so will be carrings 277v return current.