Inverter Duty Motor
An inverter duty motor is a motor specified to be supplied from a variable frequency converter rather than directly from the mains, with its insulation system, cooling arrangement and usable speed range all defined for converter operation.
A converter output is not a sine wave. It is a train of steep-edged pulses, and by the time those pulses reach the motor terminals along a cable they can arrive with a peak considerably higher than the drive produced. The insulation has to survive that, repeatedly, for the life of the machine.
The second difference is cooling. On an ordinary machine the fan sits on the shaft, so it slows down exactly when the machine is running slow and still has losses to shed. That is why inverter duty machines are commonly built with a separately driven fan running at constant speed.
Also written: inverter duty motors · VFD motor · variable frequency motor · inverter rated motor · vfd electric motor
What the term fixes, and what it leaves open
| Supply | Converter output — pulse-width modulated, not sinusoidal |
|---|---|
| Insulation | Specified for repeated voltage peaks caused by cable reflection at the terminals |
| Cooling | Commonly IC416 — a separately driven fan at constant speed, independent of motor speed |
| Speed range | Constant torque below base frequency, constant power above it |
| LEADGO YVP window | Constant torque 5 – 50 Hz; constant power 50 – 100 Hz |
| Efficiency measurement | A separate standard — tested against a standardised comparable converterIEC 60034-2-3:2024 |
| Efficiency class | Machines designed specifically for converter supply are excluded from the line-fed IE classesIEC 60034-30-3:2024, clause 1 |
| Is "inverter duty" a certification? | No. No standard issues the label — it is a description of how the machine was specified |
Three different problems in three different places
Converter operation causes trouble at three points, and the fix for one does nothing for the others. On the supply side, the drive draws harmonic current from the grid. At the motor terminals, cable reflection raises the peak voltage the insulation sees. At the shaft and bearings, common-mode voltage can drive current through the bearings.
Line reactors, dv/dt filters and insulated bearings each address exactly one of those. Specifying "an inverter duty motor" does not by itself settle any of them — it settles the machine, not the installation.
What the efficiency figure on an inverter duty datasheet means
It is measured against a standardised reference converter, so that two machines tested in two laboratories are being asked the same question. The standard is explicit that this makes designs comparable with one another, and equally explicit that it is not the loss figure for your installation.
Knowing the real losses in a specific drive means testing the whole power drive system with the converter that will actually be used. That distinction is worth raising before a guarantee is written around a datasheet number.
What Inverter Duty Motor does not tell you
"Inverter duty" is not a class or a certificate
No standard defines the phrase or issues a mark for it. It describes an intention. What makes it checkable is the specifics underneath: the insulation system, the cooling code, and the constant-torque and constant-power windows in hertz.
It does not mean any drive will do
The machine is specified for converter supply in general; the installation still has to match a particular converter. Cable length, switching frequency and converter topology all change what arrives at the terminals.
It does not mean the machine is a permanent magnet machine
Induction and permanent magnet machines are both built for converter duty. Which one you have is a separate axis, and it changes the drive requirement completely — a PM machine needs a converter that can track rotor position.
It does not remove the need for ancillaries
Reactors, filters and bearing protection sit outside the motor. A machine rated for inverter duty is not a substitute for deciding whether the problem is on the supply side, at the terminals, or at the shaft.
Which LEADGO motor series are built for converter supply
Generated from the product data. Drives and control cabinets are excluded — they are the other half of the system, not motors. The cooling code is shown because it is the part most often left unspecified, and it is what decides whether the machine can hold its rating at low speed.
CYJTYP Series
IC410, totally enclosed natural cooling
DZTYP Series
IC410
GTYP Series
IC416 / IC411 (air cooled)
GTYPS Series
Water cooled
TYC Series
IC411
TYP Series
IC411
TYPL Series
IC410
YBBP
IC416 (separately driven fan)
YBBPX3
IC416 (separately driven fan)
YFBBPX3
IC416 (separately driven fan)
YVP Series
IC416 (separately driven fan)
Frequently asked
What is an inverter duty motor?
A motor specified to run from a variable frequency converter rather than straight from the mains. What differs is the insulation system, which has to survive repeated voltage peaks from the converter; the cooling, which usually cannot rely on a shaft-mounted fan at low speed; and the defined speed range, stated as a constant-torque window and a constant-power window in hertz.
Is inverter duty a certification?
No. No standard defines the phrase or issues a mark for it, which is why two motors both described as inverter duty can be specified very differently. The checkable parts are the insulation system, the cooling code, and the two frequency windows — ask for those rather than for the label.
Why does an inverter duty motor need a separate fan?
Because a fan on the motor’s own shaft slows down with the motor. At low speed the machine still has losses to get rid of, but the cooling has fallen away with the speed. A separately driven fan — cooling code IC416 — runs at constant speed whatever the main machine is doing, which is what lets the machine hold its rating across the speed range.
Can I use a standard motor on a VFD?
Often, within limits, and the limits are the point. The cooling has to be checked at the lowest speed the machine will actually run at, and the peak voltage arriving at the terminals depends on the cable and the converter. Neither is a yes-or-no property of the motor, which is why a wide speed range or a long cable is usually where a standard machine stops being suitable.
Do inverter duty motors have IE efficiency classes?
Machines designed specifically for converter supply are excluded from the line-fed efficiency classification, so there is often no IE class to quote. Converter-fed efficiency has its own test standard instead, measured against a standardised reference converter — a figure that compares designs with each other rather than predicting the losses in your installation.
Where this is worked through properly
What an inverter-duty efficiency figure measures →
the comparable converter, and its limits
VFD reactors and filters →
which of the three problems you actually have
Drive system efficiency, IE and IES →
classifying the system rather than the motor
VFD retrofit: induction or PM →
what an existing installation forces on the choice
Flameproof motors on a VFD →
where the speed window narrows, and why