On 02/09/2011 03:00 PM, Jon Danniken wrote:
If an electric motor with 80% efficiency is pulling 16A at 120V, what is the
horsepower?

Going by (16)(120)(0.8)/746, I get about 2 HP.

Is this right?
Unless you measure the current with a phase-sensitive ammeter, you are
measuring two totally unrelated values. The problem with AC (I'm
assuming from "120 V" that this is an AC motor) is that the phase angle
is extremely important. Many motors will have only a small variation in
measured current from no-load to full load. the difference is that the
phase angle between voltage and current shifts dramatically from no load
(current lags nearly 90 degrees from voltage) to full load, where
current and voltage are nearly in phase. The POWER drawn changes just
as dramatically, from maybe 200 Watts to 1900 W. But, you will likely
see a 2 HP motor will draw 11 - 13 A at idle.

Jon