The class on a rating plate is a compliance threshold, not a running cost. Buy the efficiency the operating hours can repay. A 15 kW machine at 4,000 hours a year spends about 860 kWh more on IE2 than on IE3, so settle the frame, the starter and the drive before assuming an upgrade pays.
What the four classes define
IEC 60034-30-1, adopted in Europe as EN 60034-30-1, grades single-speed line-operated motors from 0.12 kW to 1,000 kW, in 2, 4, 6 and 8 poles, on 50 or 60 Hz supply and rated voltage from 50 V to 1 kV. The 2014 edition set four classes and pulled single-phase and line-start permanent magnet machines into scope; IE5 appeared the same year as an indicative target rather than a limit.
| Class | IEC name | Where you still meet it | Market position |
|---|---|---|---|
| IE1 | Standard efficiency | Pre-2000 plant, small machine tools, spares for old imported equipment | Below the legal floor in the EU and China for 0.75 kW and above |
| IE2 | High efficiency | Installed base from 2010 to 2020, pump and fan sets, sub-1 kW machines in the EU | Legal minimum in the EU only in the 0.12 to 0.75 kW band |
| IE3 | Premium efficiency | Conveyors, geared motors, general process drives | The floor from 0.75 kW in the EU and China |
| IE4 | Super-premium | Fans, pumps and compressors on high-hour duty | Required for 75 to 200 kW in the EU since July 2023; voluntary elsewhere |
| IE5 | Ultra-premium | Synchronous reluctance and permanent magnet machines on a drive | Limits added in the 2025 edition; narrow product range |
The percentage behind a class is not fixed, because the standard sets a separate limit table for each output and pole count. Take 4-pole 50 Hz, where IE3 is 82.5 % at 0.75 kW, 92.1 % at 15 kW and 95.0 % at 75 kW. A bare class name with no power and pole count attached is not a specification. Those figures are minimum efficiencies at rated output, measured by the low-uncertainty method of IEC 60034-2-1, and a motor is placed in a class on the lowest efficiency it achieves across its ratings.
Four things the class does not tell you:
- How the motor behaves away from rated load. Part-load curves differ between designs, and a pump throttled to half flow is not running where the plate was measured.
- What happens on a converter. The class is defined on sinusoidal supply; the losses and the part-load behaviour under a drive are a separate question.
- How it starts. Locked-rotor current and starting torque are not part of the class, and they are exactly what an old starter cares about.
- Whether it fits. Frame, shaft, flange and terminal box are set by IEC 60072-1 and the mounting code, and no efficiency figure overrides them.
The class is a compliance question, the bill is an economic one
Two different decisions get mixed up here. Regulation decides what may be sold; running hours decide what is worth buying.
In the EU, Regulation 2019/1781 has required IE3 for motors from 0.75 to 1,000 kW since July 2021, added IE4 for 75 to 200 kW machines of 2, 4 and 6 poles in July 2023, and set IE2 for the 0.12 to 0.75 kW band on the same date. China reaches the same place through GB 18613-2020, which grades motors 1 to 3, aligns grade 3 with IE3 and grade 1 with IE5, and has been mandatory since June 2021. Both schemes govern what can be placed on the market, which is why IE1 and IE2 motors are now replacement-only items in most ratings.
Compliance ends there, and buyers rarely recognise the boundary. Whether an IE4 motor is the right purchase depends on hours and load, and on a lightly used machine the answer is often no.
What the extra points cost in metal
Efficiency is bought with active material. A higher class usually means a longer core with more silicon steel, more copper in the stator winding, a larger rotor cage and a tighter air gap. The result is a motor that is heavier and longer than the one it replaces, and on some ratings a frame size larger, which is the first thing to check before ordering.
Two consequences matter at replacement time. The first is starting. Higher-efficiency induction designs commonly draw more locked-rotor current, and the IE4 generation splits into line-start permanent magnet machines, which will not tolerate a reduced-voltage or star-delta start without the maker’s agreement, and synchronous reluctance machines, which need a drive and cannot be started direct on line at all. The second is thermal. Fewer losses mean a cooler winding, and since insulation life roughly halves for every 10 K of extra temperature, a motor running cooler at the same load has margin the old one did not.
The arithmetic, on a 15 kW duty
Annual energy is shaft work divided by efficiency, and the rest is multiplication:
annual cost ≈ (P × load factor × hours ÷ efficiency) × price per kWh
Take a 15 kW 4-pole motor driving 12 kW of shaft load, 4,000 hours a year, at ¥0.80 per kWh. The efficiencies are the IEC minimum values for that rating, and the load is assumed to sit at the same 80 % point for all three classes, which flatters the comparison slightly because part-load curves differ.
| Class | Min. efficiency | Input at 12 kW shaft | Annual energy | Annual cost | Saved against the class below |
|---|---|---|---|---|---|
| IE2 | 90.6 % | 13.25 kW | 52,980 kWh | ¥42,380 | — |
| IE3 | 92.1 % | 13.03 kW | 52,120 kWh | ¥41,690 | 860 kWh, about ¥690 |
| IE4 | 93.9 % | 12.78 kW | 51,120 kWh | ¥40,900 | 1,000 kWh, about ¥800 |
Two readings follow. The two steps are worth about the same in cash at this rating, because a 1.5-point gap and a 1.8-point gap remove a similar share of the losses. And the absolute number is small: a few hundred yuan a year on a 15 kW machine.
Hours are the multiplier. Double the running to 8,000 hours and the two steps save 1,730 kWh and 2,000 kWh, or roughly ¥1,380 and ¥1,600 a year. Halve it to 2,000 hours and the savings fall to about ¥345 and ¥400, which is where an upgrade rarely pays. Payback is the price premium divided by the annual saving, so it shortens in direct proportion to running hours, and a two-shift fan or a process pump is a different proposition from a standby unit.
Treat the result as an order of magnitude, not a quote. Efficiency at 80 % load sits below the rated figure, the two classes do not fall away at the same rate, and where the tariff charges for reactive power the power factor needs checking with the drive supplier.
Replacing a motor that carries no IE label
An imported machine from the 1990s often has a plate with a power rating, a voltage and nothing about efficiency. The replacement is chosen on fit first and class second, and these are the items to record before looking:
- Frame size and shaft. IEC 60072-1 frame number, shaft diameter and length, keyway, and for flanged motors the flange spigot and hole circle.
- Power, speed and poles. Rated kW, rated rpm, and whether the load needs the same breakdown torque.
- Mounting. The IM code — B3 foot, B5 flange, B14 face, B35 foot and flange — and the terminal box position on the frame.
- Enclosure and cooling. IP rating, and the IC code, since a TEFC motor (IC411) and a separately ventilated one are not interchangeable in a dirty or hot location.
- Insulation and duty. Class and temperature rise, usually F with B rise, plus S1 continuous or a shorter duty cycle.
- Supply and start. Voltage, frequency, connection, and whether the existing starter is direct on line, star-delta or a soft starter.
Where the original class is unknown, an IE3 unit is normally the right commercial choice in the EU and China, and it will be heavier than what comes out. Check the baseplate and the coupling alignment allowance before assuming the frame will drop in.
When the motor sits behind a drive
A converter changes the ground rules, and it is where most retrofit problems appear.
The supply is no longer sinusoidal. Fast switching edges stress the winding, so for a standard motor check the permitted cable length and fit a dv/dt or sine filter on long runs; motors built for converter duty are specified to IEC 60034-25, which sets an insulation requirement rather than a class label.
Shaft currents rise with frame size and switching frequency. From roughly frame 160 upwards, insulated or hybrid ceramic bearings and a shaft earthing brush belong in the specification rather than in a later failure report.
Cooling falls away with speed. A shaft-mounted fan gives almost nothing below half speed, so a motor that must hold torque at low rpm either carries a separate fan or is derated. And an IE4 synchronous reluctance machine only runs on a drive, which makes the drive part of the replacement rather than an accessory.
Where the class is no longer the question
The class compares motors, not systems. Three cases fall outside it.
Steppers, servo motors and integrated motor-drive units fall outside IEC 60034-30-1, which covers single-speed line-operated machines. A NEMA 23 stepper or an integrated unit such as the Anaheim MDrive23 has no IE class, because its losses depend on the drive, the current setting and the motion profile. Compare those on torque, current and duty instead — our Anaheim range is a case in point, while the motor category covers the line-fed machines the classes apply to.
Geared motors move the question to the gearbox. A 1:100 worm unit loses more in the mesh than an IE3 to IE4 step gains in the motor, so the ratio and the gear type decide the bill, not the class.
Pumps and fans move it to the system. Throttling a valve throws away more than any class step recovers, and a drive cutting speed by 20 % on a centrifugal load beats an IE4 motor at full speed. Fix the system first.
Putting the enquiry together
Send the nameplate photograph, the measured load and the annual hours, plus the frame, mounting and starter details from the list above. That is enough to place the right class on the right frame rather than the nearest stocked size. For the mechanical side of matching an obsolete unit, the notes on cross-referencing a motor after discontinuation cover the nameplate fields in more detail, and the full product index shows the other categories we cover. Send the details through the enquiry form and we will come back with the frame, class and options that fit the duty.
Efficiency values quoted here are the minimum limits of IEC 60034-30-1:2014 for 4-pole 50 Hz motors, as published in manufacturer reference tables, and the regulatory dates follow Regulation (EU) 2019/1781 and GB 18613-2020. Standards are revised and national scope differs, so confirm the class, the test method and the marking against the current edition of the standard and the motor’s own data sheet before ordering. This article is technical guidance, not a substitute for the standard or the data sheet, and it is not a statement of availability for any individual part number. FINACO supplies motors and drives through the manufacturer and established channels; we are an independent supplier, not the manufacturer.