i'm bidding on a 36 x 36 pole building 6-8' florescent t8 12 recp. my question is there a calculation formula for outbuidings, i'm running #4 al to a 60 amp main breaker sub panel i'm thinking maybe 20 25 total load. The thing that got me thinking was at home depot i read a sign that said #4 thhn al and #6 thhn cu is good for only 50 amp. theres nothing wrong with feeding a 60 amp panel with #4 thhw al or #6 thhw cu is there. correct me if i'm wrong but don't you size the feeder on the calculated load, then you can upsize to the next size breaker