Quote Originally Posted by J.R. Rutter View Post
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Third question - If you put a higher HP motor on the exact same load, will the amp draw be higher if motor efficiency is the same?...
The amperage an electric motor draws, in normal operation, is porportional to the load. The motor doesn't develop any more HP (or draw more amperage) than it needs to keep it's RPM near the rated value. So, if the overall efficiency is the same in both, a bigger motor won't draw more amperage than a smaller motor when both are driving the same load. That assumes of course, that both are the same voltage - a 120v motor will draw about twice the amperage of a 240v motor when both are identically loaded.

I have a 5 HP motor driving a blower impeller sized for 2 HP. I've checked the amperage draw of that motor with the impeller under full load. Considering efficiencies, the amperage draw (about 8 amps at 240v) is consistent with developing about 2HP.