Answer by Hugh Falkner (Atkins)
The IE labelling scheme for motors is described in IEC60034-30-1 Rotating electrical machines – Part 30-1: Efficiency classes of line operated AC motors (IE code). Although not published until March 2014, the efficiency levels contained within it had been used for many years by regulators and manufacturers. The tremendous benefit of this internationally recognised standard is that it gives motor buyers and sellers alike a simple way of describing how efficient a motor is. Very simply, the higher the IE number, the more efficient the motor is. It supersedes the previous EU Eff 1 – 3 scheme .
The principle underpinning the setting of the IE levels is that of fairness, meaning an equal degree of techno-economic challenge to the motor designer for all sizes and types of machine of a particular IE level. Overall this has been achieved, but all motor manufacturers report that higher IE levels are easier to achieve for large motors than for small motors. For this reason, the new MEPS for induction motors in the EU is in two stages, with motors below 7.5kW being subject to a tougher level at a later date.
There are two sets of curves, one for 50Hz (European) and another for 60Hz (primarily USA) motors. 60Hz machines run 20% faster than a 50Hz machine, and since Power = Torque x Speed, the higher speed means that for the same torque and amount of active material, the same machine can produce more power. To ensure a level playing field between motors designed for different frequencies, the 60Hz IE efficiency values are therefore set slightly higher.
For each mains frequency, there are also different IE values according to the number of poles. Again, this is so that the relative cost of manufacturing each IE level is roughly the same, where slower motors with a larger number of poles and hence more active material will be more costly.
Some motors may also have several different efficiencies specified on their nameplate, dependent on what frequency and/or voltage is used. If only one efficiency is to be declared, it must be the lowest efficiency.
If a new motor has no IE rating, then it is usual to assume that it is worse than IE1. This level is sometimes informally referred to as “IE0”; but this definition does not appear within the standard.
In common with many other standards, IEC60034-30-1 only publishes tables of values rather than a graph, but such graphs are readily available from a wide range of sources.
IEC60034-30-1 is designed very much with the induction motor in mind, and to date the IE labels are only found on induction motors. But manufacturers of other types of motors, in particular newer types of motors driven by Variable Speed Drives (VSD), are also using it to indicate how efficient their products are. Unfortunately without an agreed test standard for VSDs, these claims are not formally valid, and in any case this standard is specifically for line-driven motors only. However, a future IE5 level is mentioned in an annex, which might at a later date be created as Part 2 of this standard to enable electronically controlled motors of any type to use the same classification. The level would be set to have losses about 20% below that of the IE4 level, which is a similar ratio as the average difference between the other IE levels.
 Where IE1 = Eff 2, IE2 = Eff 3.