Unlike the previous standard, which was based partly on estimated values, the new IEC/EN 60034-2-1 standard is based on measured values of losses. For example, winding and rotor losses will determined by measuring temperature rises.

The standard also tightens up on calculations of additional load losses that result from the magnetic flux created as a motor is running. Previously, these losses were estimated at 0.5% of the input power at the rated load. This resulted in efficiency figures that were generally too high.

The new standard allows for the additional losses to be measured and requires motor manufacturers to state how they have measured their efficiency values. Accurate measurement of the additional losses is expected to result in slightly lower efficiency figures for many motors – although this does not mean that the motor’s design or performance has changed.

Some motor manufacturers have already started to re-test their motors to the new standard. ABB, for example, is using accurate equipment to measure the additional losses and plans to publish the new efficiency values in its catalogues during 2008.

"We welcome the fact that the efficiency measurement standards for electric motors are becoming more harmonised worldwide," says ABB’s Steve Ruddell. "We have waited a long time for a level playing field to be introduced."