The comparison of motors based on their efficiency could be complicated and the outcome may be completely worthless. Our initial decision was not to publish any Energy Saving Calculator on our website but a number of our customers asked for it so we eventually decided to publish it but not without the following explanation:

The efficiency of electric motors was originally calculated as the ratio between the shaft output power and the electrical input power into the motor. However a new IEC 60034-2:1996 efficiency standard stipulating calculation/testing method was published in 1996 where the efficiency was established through the summation of motor losses. The additional losses were then added as fixed percentage (0.5%) of the measured losses. By using the summation of losses the motor efficiency value was actually lower than the efficiency value calculated when the traditional method was used.

In 2007 a new efficiency determination method was introduced when the new IEC 60034-2-1:2007 standard was published. The motor efficiency must again be determined through summation of losses however the additional losses can no longer be added as a fixed percentage but must be measured/calculated and the motor efficiency is lower when this new method is used than when compared with the previous method specified in IEC 60034-2 standard. The efficiency value difference is between 1%-2% which is actually quite a substantial figure.

When you try to compare a modern motor efficiency of which was determined through the IEC 60034-2-1 and an old motor the efficiency of which was determined through IEC 60034-2 or if the motor was produced before 1996 before the IEC 60034-2 efficiency standard was published you will be comparing incomparable. If the old motor was tested today whilst using the latest efficiency testing standard the efficiency would be considerably lower than the one published on the motor's rating plate at the time of manufacture.