The 3 Most Important Variable Frequency Drive Limitations

Variable frequency drive limitations are a serious concern for anyone who uses VFDs. I know from experience that many people don’t understand just how important it is to use the proper motors with their variable frequency drives. There are several common misconceptions about these Vfd Motor Control devices, but none more so than what a motor should be rated for before using one with a variable frequency drive. 

In this article, we’ll explore some of these limitations and show you what to look out for so that you can choose the right motor for your project.

Not all motor rated motors are VFD Rated.

Not all motor-rated motors are VFD rated. This can be a very costly mistake to make, especially if you’re replacing an old standard starter/contactor with a new variable frequency drive.

The Motor Protection Device (MPD) is the device that protects your motor from being damaged by overheating and overloading. The MPD is included inside the motor and must be reset once it has tripped to allow the motor to start again.

Most Vfd Motor Control manufactured today use an internal overload protection device that trips when the current exceeds its rating and resets automatically when cool. 

However, some older motors do not have this type of protection built in and require separate overload protection devices on the line side of each phase connection to protect against high starting currents (e.g., capacitor start motors). 

These types of capacitors should never be used for VFD applications because they can cause an electrical arc when they fail or trip off during operation, which could potentially damage equipment connected downstream from them!

Vfd Motor Control

Careful attention to ambient temperatures.

VFDs are sensitive to ambient temperatures and can be damaged by overheating, freezing, vibration and moisture. VFD motor controls should be installed in a cool location with good air circulation. 

When installing the control, it is important that all components are mounted level and not subject to vibration or excessive movement.

Motor rating considerations

In order for a frequency converter to provide adequate power transfer capability between itself and the motor is controlled, it must have enough capacity within its own drive system (gear box size / torque rating). 

Manufacturer overload ratings can be inaccurate.

VFDs are not always 100% efficient and can be damaged by overloading.

They can also be damaged by overheating, low voltage or phase imbalance between the voltage and current in the motor.


Careful attention to ambient temperatures, manufacturer overload ratings and VFD limitations can help you avoid these common pitfalls. Hope you found the blog useful in understanding about Variable Speed Drive and vfd motors.

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