A 10KVA single phase transformer would provide 83A per line with a 120V 2 wire connection. Or, you could have 42A per line with a 120/240 3 wire connection.
I am not aware of any 10KVA three phase transformer, so I don't know what the contractor was trying to install. You would need a 30KVA unit to get a single voltage secondary of 83A at 120V. It would not be possible to have a 120/240 3 wire secondary connection with this unit. Also, this arrangement would not be very energy effcient and would require a much larger primary feed.
