I’m installing a 240 volt, 30 amp line for my Ovation kiln

Since you are firing to such low temperatures, it would probably be okay to fire your kiln on only 214 volts. Try to fire the kiln as is. If the kiln cannot reach the temperatures you need, you could change the 240 elements to 208 volts. If you install 208-volt elements, obtain a new electrical data plate for your kiln that shows 208 volts.