Don't worry too much about what the POCO is is supplying you with now. Provide them with a real load calculation and they will determine which size wires to run to your service.
But for kicks... (I x E = P)
(480V x 1.732) x 100 amps = 83Kva
83,000va/ (208V x 1.732) = 231 amps
Looks like you're good to go with what's there but you'll still need to supply the calc load to the poco.
“It marks a big step in your development when you come to realize that other people can help you do a better job than you could do alone.”
-- Andrew Carnegie