An accurate method of estimating the efficiency of in-service motors is needed in order to determine the
performance of installed motors without disrupting the motor driven process. In this paper, the motor
efficiency is estimated using a non-intrusive implementation of the compensated slip method. The motor
speed is accurately estimated using motor vibration signature analysis. A few other efficiency estimation
techniques are implemented and their performance is compared to the proposed method. It was found
that the non-intrusive compensated slip method produced relatively accurate results without having
an adverse impact on the availability of the motor under test. This method provides an attractive alternative
to highly intrusive techniques that offer similar accuracy.