A/C condensing unit calculation

[Minuteman]

Amps is not = watts/voltage. You're missing power factor, and that is significant on a motor-compressor.

I have not found a single equation that works well. Dividing the BTU by 8.5 is rather close to come up with VA. But it is best to find the MCA value. I'd hate to install 10-2 thinking it would be be in the high 20's for amps only to see an MCA of 30.5. Or you install 8-2 to cover your bets and see an MCA of 24 so you could have used 12-2.

Totaly agreed.

I only use the 10 amps per ton for bidding. Nameplate is the ONLY correct way to know what size conductors and OCP to install.