Given a 208 VAC, 3 phase circuit, with amperage on a, b, and c phases, how do you calculate total KVA? Do you use the average of the 3 amperage readings or do you base the calculation on the leg with the highest amperage? Or...
Thank you for your attention to this question

Ideally this should have been posted under the Electrical section in Home and Garden, lot more people would view it there. I googled your question and found 300,000 hits. You might try there first. While I do electrical work, I do not do 3 phase.