Don'tknow;
without gettin' the good book out, i believe you must size per ballast, not element.
( probably because people can change an element)
then you should use the 80% rule for totals as applied to circuits.
yes, a shared noodle can have it's drawbacks, not that it's a violation. There is the consideration of the electronic ballasts vs. regular ones, i think they create more harmonics....

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