GB 18613 and IE Classes: Reading a Chinese Efficiency Grade

Two efficiency systems meet on most Chinese motor quotations, and the first thing to know about them is that their numbers run in opposite directions.

Direct answer

GB 18613—2020 defines three energy-efficiency grades for motors, and states plainly in its definitions clause that grade 1 is the highest efficiency. The scale improves as the number goes down.

The IE code runs the other way. As GB/T 32891.2—2019 puts it in its foreword, the intention is a single system in which IE1 is low efficiency and IE5 the highest — and the code is not limited to motors: it is applied to other products such as converters and gearboxes as well.

So “grade 2” and “IE2” are not two names for a similar thing. They sit at opposite ends of their respective scales.

Neither one is a label

This is the part that matters more than the direction, and it is the reason we are not going to print a tidy grade-to-IE lookup table here.

Both systems define their classes as tables of efficiency values indexed by rated power, pole count and frequency. GB 18613 adds two mechanics that any comparison has to respect:

• Ratings not listed in the tables are determined by linear interpolation.
• The measured efficiency at rated output carries a tolerance, per GB/T 755 and the relevant product standard.

So a statement that two classes “are the same” is a statement about a particular table cell, plus a tolerance — not about the words on a nameplate. At your power, your pole count, your frequency, compare the two numbers. That comparison takes five minutes with both standards open, and it is the only version of the answer that survives an engineer checking it.

If a supplier offers a general equivalence without reference to a rating, treat it the way you would treat any other unqualified claim.

Cite the right part, or you cap yourself at IE4

GB/T 32891 comes in two parts, and the split is by how the machine is fed:

Part 2 covers machines designed to run on sinusoidal fundamental current but not directly on the line — permanent magnet synchronous machines with or without additional reluctance torque, sinusoidal reluctance synchronous machines, and synchronous machines with DC field windings, plus induction machines specifically designed for variable-speed operation. Switched reluctance machines are not included.

Two consequences for a specification:

• Quoting an IE class for a PM or inverter-duty machine from Part 1 caps the claim at IE4 when the machine may qualify higher under Part 2.
• A machine that uses a converter only to soft-start and then runs on the line is not in Part 2’s scope — that case goes back to the line-operated part.

Explosion-proof machines: the trade-off is in the standard

This is worth knowing because it usually arrives as an argument rather than a fact.

GB/T 32891.2 states that motors designed to IEC 60079-0 for explosive atmospheres are covered by the standard, and then explains that the special design considerations these machines carry for safety — a larger air gap, reduced starting current, enhanced sealing — mean they may not be able to reach the higher efficiency classes.

That is a documented engineering trade-off written into the classification standard itself. A hazardous-area machine sitting a class below its general-purpose equivalent is not a supplier falling short; it is the physics the certification requires.

A high class is not the same as saving energy

The same standard is unusually direct about the limits of its own scale, and two of its statements deserve to be read by anyone writing an efficiency specification:

A high-efficiency motor does not by itself make a high-efficiency system. The standard coordinates with IEC 61800-9-2, which classifies converters (CDM) on an IE scale and complete power drive systems (PDS) on an IES scale. Users are advised to select the motor’s efficiency class against the actual load and operating point, and the running hours.

On the wrong duty, a high class can be the wrong purchase. Where operation is short-time, intermittent, or substantially at part load, choosing a high-efficiency-class motor rated for S1 continuous duty is not necessarily energy-saving.

There is a physical reason behind the second point, and the standard gives it: to reach higher full-load efficiency, these machines run a moderate flux density, which makes them physically larger with higher rotor inertia than standard-efficiency machines. On a duty dominated by acceleration rather than by steady running, that extra inertia is a cost, not a benefit — which is why servo machines are excluded from the scope entirely.

If your duty is cyclic, settle the duty type first. See motor duty types S1 to S10.

What the scope leaves out

Worth checking before an efficiency clause is written into a contract, because several common machines are simply not in it:

• Motors with mechanical commutators.
• Motors integral to combination machinery — pumps, fans, compressors — that cannot be separated and tested on their own.
• Brake motors where the brake is an internal structural part that cannot be removed or separately powered during the efficiency test. Brake motors are included where the efficiency can be measured without the brake’s losses, for instance by removing the brake or powering the coil from a separate supply. (See brake motors: how the brake releases.)
• Motors designed to run fully immersed in liquid.
• Smoke-extraction fan motors above the 400 °C temperature class.
• Machines meeting the standard’s quantitative servo criteria.

Two reference conditions also travel with every published figure: rated efficiencies and classes are given at an ambient of 25 °C and referenced to an altitude at or below 1,000 m. A site that departs from either is not reading the same number.

On NEMA Premium, since it always comes up

MG 1’s Premium efficiency tables are not a single object. The 50 Hz values are stated in the standard as derived from IE3. The 60 Hz table is NEMA’s own.

So the correct sentence is that the 50 Hz Premium level has a stated IE3 basis — not that NEMA Premium and IE3 are numerically the same thing across the board. The second version gets refuted the moment someone opens both tables.

What to ask for

1. The class, the standard, and the edition — GB 18613 grade, or IE class from Part 1 or Part 2, named explicitly.
2. The efficiency value at your rating, not the class alone.
3. The test method and tolerance applied.
4. The duty, so that the class is being chosen against real running hours rather than a nameplate.
5. For hazardous-area machines, whether the class reflects the Ex design trade-off above.

LEADGO’s YE5 and YE4 series carry their grades per rating rather than as a family claim — ask for the efficiency at the specific power and pole count you are buying, and compare that number against whichever system your market uses.

Going deeper

• Motor duty types S1 to S10 — where the part-load and intermittent cases above are defined
• NEMA MG 1 explained — how the US standard defines a premium efficiency motor
• Brake motors: how the brake releases, and what fails — the machine the efficiency scope treats conditionally