I read the Mike Holt forum post ?Primary protection of xfmr? I want to step down 480 volts to 208 volts single phase. I need 23 per leg amps on secondary, the amp draw on the primary side is 10.4 amps table 450.3(B) states 125% for primary OP and 250% when both primary & secondary OP devices are used if transformer has primary thermal overload. I have not received the equipment, not sure if thermal protection is installed. I want to protect the transformer from overload by feeding with a 15 amp OP primary and a 20 amp for secondary OP work if no thermal protection is installed. Can any confirm I am on the right track Thanks?