One horsepower is 745.7 watts. which translates to 6.214 amps at 120V.
At 80% mechanical efficiency, it the draw is 7.767 A. de-rate another 20%
for phase angle, and the apparent draw is 9.70A. multi-horsepower, poly-
phase motors will achieve overall efficiency in the 90% range; on the other
hand, 75% is *extremely good for a 1-to-2 HP single-phase unit -- 57-65 is
much more typical int that power range. And at small fractional HP (say
1/6-1/4 HP), getting 50% efficiency is a major accomplishment.
A circuit breakered at 20A is limited to plug-in devices drawing no more than
18A 'Full load', per NEC. At 120V, that gets a 'theoretical' 2.89HP, under
perfect conditions. A 2-1/4 to 2-1/2 HP load on that circuit requires
overall efficiency in the 80-85% range.
*NOT* 'impossible'; but *is* 'bloody unlikely'. <grin>
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