Original poster: "Steve White by way of Terry Fritz <twftesla-at-qwest-dot-net>" <slwhite-at-zeus.ia-dot-net> Can anyone tell me how many square inches of iron (stell laminations) is needed for the center section of a ballast. The ballast is to be used for a 5 KVA pole transformer. I want to limit the current at 20 to 25 amps at a working voltage of 240 volts.