VFD Fault Diagnosis and Troubleshooting Guide

VFD Fault Diagnosis & Troubleshooting Guide | Common VFD Alarms, Causes, and Solutions

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Introduction:

Variable Frequency Drives (VFDs) play a critical role in modern industrial automation by controlling motor speed, torque, and energy efficiency. However, VFD faults and alarms can interrupt operations, reduce productivity, and damage equipment if not addressed correctly.

VFD Fault Diagnosis and Troubleshooting Guide

This comprehensive VFD fault diagnosis and troubleshooting guide explains common VFD alarms, root causes, and step-by-step solutions, helping maintenance engineers, technicians, and automation professionals quickly restore normal operation and improve system reliability.

What is a VFD Fault?

A Variable Frequency Drive (VFD) fault occurs when the drive detects abnormal operating conditions such as overcurrent, overvoltage, overheating, or communication failure. The drive automatically stops the motor to protect electrical components and connected equipment.

Common VFD faults include:

Overcurrent fault
Overvoltage fault
Undervoltage fault
Overtemperature fault
Ground fault and more.

1. Current Limit 🔧

The drive enters current limit mode. This means the motor current has reached the set limit.

Current Limit

Check Current Limit Settings.

If Yes (If OK):

Check Motor, Load, and Drive Size.

Verify:

Motor rating matches the drive,
Mechanical load is not excessive,
Drive capacity is sufficient for the application,

If No (If Not-OK):

Correct Settings

Adjust current limit parameters to proper values.

Restart the Drive

Check Current Limit?

If Yes (If OK)

Perform Motor Identification

Run motor auto-tuning / identification.
This allows the drive to correctly control motor current.

If No (If Not-OK)

▶️ Restart the Drive

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2. Drive Not Getting to Speed 🚀

Start when the VFD fails to reach the commanded speed.

Drive Not Getting to Speed

Check Current Limit or DC Bus Limit

If Yes (If OK)

Check Motor current

DC bus voltage

If motor current is OK and DC bus voltage is OK → Continue checking.

If motor current or DC bus voltage is NOT OK → Investigate and correct the issue.

Finally check the Speed.

If No (If Not-OK): Continue Next Process

Check Analog Input Reading

Is the analog input signal being read correctly?

If Yes (If OK): Continue Next Process

If No (If Not-OK): Check wiring

Loose terminals
Damaged cable
Wrong polarity
Incorrect signal type

Finally check the Speed.

Check Reference Source Settings

If Yes (If OK): Continue Next Process

If No (If Not-OK):

Correct the reference source settings.

Finally check the Speed.

Check For Preset Speed Command

If Yes (If OK): Remove fixed speed (preset speed) command.

If No (If Not-OK): check the Speed.

Check Speed:

Verify that the drive receives the correct frequency reference and accelerates normally after all corrections.

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3. VFD Drive Does Not Start ⏳

VFD Drive Does Not Start

Check if the Drive is Ready?

If Yes (If OK):Continue Next Process.

If No (If Not-OK):

Check for Active Fault

If a fault exists, then clear the fault,

If Yes (If OK):

check DC Bus voltage.

If Yes (If OK):

Ensure Run Enable input is active.

If Yes (If OK):

Restart the Drive.

Check Start Source Settings

If Yes (If OK):Continue Next Process.

If No (If Not-OK):

Correct the start source settings.

Next Restart the drive.

👉Check the Control Place (Control Source)

If Yes (If OK):Continue Next Process.

If No (If Not-OK):

Correct Settings.

Next Restart the drive.

Check the Start Signal

If Yes (If OK):Restart the drive.

If No (If Not-OK):

Ensure the start command is active and check wiring

Loose terminals
Open contact
Incorrect input type
Damaged cable

Restart Drive:

Once all checks are correct:

Restart the drive
Verify the RUN command
Confirm that the drive starts normally

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4. Ground Fault Detected ⏚

Ground Fault Detected

Check Motor Leads

If Yes (If OK):Continue Next Process.

If No (If Not-OK): Correct Cabling

Fix loose wires
Replace damaged cables
Verify phase sequence
Check insulation

Next Restart the drive.

Disconnect Motor Leads & Restart Drive

Disconnect the motor from the drive and restart the VFD.

This helps determine whether the fault is coming from the motor or the drive.

Check Again: Is Ground Fault Still Present?

If No (If Not-OK):

Check the Motor
Motor insulation test (Megger)
Check for winding short-to-ground
Replace or repair the motor
You may also test the drive using a known good motor

Next Restart the drive.

If Yes (If OK):Current Measurement Fault in Drive

If the drive shows ground fault even with motor disconnected:

This indicates:

Internal current-sensing failure
Internal short
Faulty IGBT module
Drive control board issue

This generally requires:

Drive repair
Component replacement
Drive replacement (if not repairable)
After correcting the issue (motor or drive), restart the VFD and test operation.

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5. Input Phase Fault Detected 🔌

The drive has detected an input phase loss or imbalance.

Input Phase Fault Detected

Check Line Voltage

If No (If Not-OK):

Correct Input Voltage

Fix supply imbalance
Restore missing phase
Correct loose terminals
Restore proper mains connection

Then Restart the drive.

If Yes (If OK):Continue Next Process.

Static Checks OK?

Perform Static Checks this includes checking:

Input fuses
Input rectifier
Contactor connections
Supply wiring continuity
Phase sequence

If No (If Not-OK):

Replace Faulty Components

Possible faults include:

Blown fuses
Damaged rectifier module
Burnt terminals
Open-phase wiring
After repairs,

Then Restart the drive.

If Yes (If OK):Continue Next Process.

Input Phase Fault

If No (If Not-OK):

Check for Input Phase Fault Again,

System is normal after correction.

Then Restart the drive.

If Yes (If OK):

The issue is internal to the drive.

Proceed to next step.

Measurement Fault in Drive

If the drive shows input phase fault even after voltage and static checks:

The drive has a faulty phase measurement circuit.

Possible causes:

Faulty input current sensors
Defective control board
Faulty measurement IC

This requires:

Drive repair
Component replacement
Or complete drive replacement (if repair is not possible)

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6. Motor Over Temperature Alarm🌡️

The VFD reports that the motor temperature is too high or thermal protection has been triggered.

Motor Over Temperature Alarm

Check Motor Parameters is OK?

Are the motor parameters set correctly?

Examples include:

Motor rated current
Motor thermal class
Motor power (kW/HP)
Motor frequency and voltage
Motor thermal settings

If No (If Not-OK):

Correct Parameters

Enter the correct motor nameplate data and thermal settings,

Then Restart the drive.

If Yes (If OK):Continue Next Process.

Check for Motor Overload Condition

Motor overload may happen due to:

Heavy mechanical load
Blocked fan/pump
High friction or jamming
Low cooling airflow
Incorrect speed setting

If No (If Not-OK):

Check Motor Thermal Overload Parameters

Ensure that:

Thermal model settings are correct
No false overload conditions
Cooling fan and airflow are normal

Then Restart the drive.

If Yes (If OK):Reduce Motor Load:

If actual overload is confirmed, Reduce the load by:

Removing mechanical blockage
Reducing torque demand
Fixing jammed equipment
Improving motor cooling
Adjusting process load

Once load is corrected Restart the drive.

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7. Output phase fault⚠️

Output phase fault

Disconnect Motor Leads

Disconnect the motor cables from the drive output terminals.

This isolates the motor and wiring from the drive.

Output Phase Fault?

If No (If Not-OK): Check Motor and Connections

Fault is caused by:

Motor winding problem,
Cable damage,
Loose or incorrect wiring,
Ground fault or insulation failure,

Restart Drive

After correcting motor or wiring issues, restart the drive.
System should run normally.

If Yes (If OK):

Faulty Current Measurement

Fault is internal to the drive.

Possible causes:

Faulty current sensor,
Defective IGBT/output stage,
Power module or control PCB failure,

After restart the drive. If fault remains, drive requires service or replacement.

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8. Over Current 🔌

The drive trips due to an over current fault.

Over Current

Check Motor Settings

Check whether the motor parameters in the drive are correct:

Rated voltage
Rated current
Rated power (kW/HP)
Frequency

If No (If Not-OK):

Correct Settings

Enter the correct motor nameplate values in the drive.

Restart Drive

After correcting the settings, restart the drive.
Fault should be cleared.

If Yes (If OK):

Disconnect Motor Leads, Restart Drive

Disconnect motor cables from the drive.
Restart the drive without the motor connected.
This helps isolate the fault.

Over Current

If Yes (If OK): Current Measurement Fault in Drive.

The fault is inside the drive.

Possible causes:

Faulty current sensor,
Damaged IGBT or power module, Internal control board issue,

Restart Drive

Drive needs repair or replacement before normal operation.

If No (If Not-OK): Check Motor, Load, and Drive Size

The drive is OK.

Possible issues:

Motor mechanical load is too high,
Motor problem (bearing, winding),
Drive size is too small for the motor.

Restart Drive

After fixing motor/load issues,
restart the drive.

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9. Over Voltage ⚡

The drive trips due to an over-voltage fault.

This happens when the DC bus voltage exceeds the safe limit.

Over Voltage

Line Voltage OK?

If Yes (If OK):

Fault Occurs During Deceleration or When Motor Is Over-Running?

If No (If Not-OK):

Correct Input Voltage

Check incoming supply voltage.
Ensure voltage is within the drive’s rated limits.

Restart Drive.

Fault Occurs During Deceleration or When Motor Is Over-Running?

If Yes (If OK):

Increase Deceleration Time or Add Brake Chopper

Fast deceleration causes regenerated energy to raise DC voltage.

Solution:

Increase deceleration time, or Use a braking resistor / brake chopper.

Restart Drive

If No (If Not-OK): Monitor = Measured Value

Monitor = Measured Value

If Yes (If OK): Check Line Side Harmonics

Voltage spikes or harmonics from the power supply may cause over-voltage.

Check:

Power quality,
Harmonic distortion,
Line reactors or filters,

Restart Drive

If No (If Not-OK): Measurement Fault in Drive

The voltage feedback or sensing circuit inside the drive is faulty.
Drive requires repair or replacement.

Restart Drive

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10. Under Voltage ⚡

The drive trips due to an under-voltage fault.

This means the supply or DC bus voltage is below the required level.

Under Voltage

Line Voltage OK?

If Yes (If OK): Continue Next Process Static Checks OK?

If No (If Not-OK):

Correct Input Voltage

Check incoming power supply.
Ensure voltage is within the drive’s rated limits.

Restart Drive

Static Checks OK?

If Yes (If OK): Continue Next Process [ Monitor = Measured Value?]

If No (If Not-OK):

Replace Faulty Components

Possible issues:

Blown fuses,
Loose terminals,
Faulty rectifier or DC bus components,

Restart Drive

Monitor = Measured Value?

If Yes (If OK):

Check Power Quality and Proper Drive Sizing

Possible causes:

Voltage dips
Weak power supply
Drive undersized for the motor/load

Restart Drive

If No (If Not-OK):

Measurement Fault in Drive

Internal voltage sensing circuit is faulty.
Drive requires repair or replacement.

Restart Drive

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11. Unit Over Temperature 🌡️

The drive trips due to over-temperature.
This happens when the internal temperature exceeds the safe limit.

Unit Over Temperature

Cooling Fan ON?

If Yes (If OK): Continue Next Process [Heat Sink Clear?]

If No (If Not-OK):

Repair Cooling Fan(s)

Check fan power supply.
Replace faulty or blocked cooling fans.

Restart Drive

Heat Sink Clear?

If Yes (If OK): Continue Next Process [ Monitor = Measured Value?]

If No (If Not-OK):

Clean Heat Sink

Remove dust, dirt, or blockage.
Ensure proper airflow through the heat sink.

Restart Drive

Monitor = Measured Value?

If Yes (If OK):

Measurement Fault in Drive

Temperature sensor or monitoring circuit is faulty.
Drive requires repair or replacement.

Restart Drive

If No (If Not-OK):

Check Ambient Temperature of Inlet Air

Ensure surrounding temperature is within limits.
Improve ventilation or cooling in the panel/room.

Restart Drive

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Common Applications of VFD Drives

HVAC fan systems
Pump control systems
Conveyor systems
Compressors
Industrial automation equipment

Conclusion:

A systematic approach to VFD fault diagnosis significantly reduces downtime, protects equipment, and improves operational efficiency.
By understanding alarm causes and following structured troubleshooting steps, technicians can quickly identify whether issues originate from the motor, load, power supply, or the drive itself.
This guide serves as a practical reference for field engineers, maintenance teams, and automation professionals working with Variable Frequency Drives in industrial environments.

FAQ (Frequently Asked Questions)

1. What is the most common VFD fault?

Overcurrent and overvoltage faults are among the most common VFD problems.

2. Why does a VFD trip frequently?

Frequent tripping may occur due to motor overload, improper parameter settings, or unstable power supply.

3. How do you reset a VFD fault?

Most drives can be reset through the keypad, digital input, or by cycling the power supply.

About the Author – Insight Control System

Insight Control System provides technical education and practical guidance in the fields of Building Automation Systems (BAS), HVAC controls, PLC programming, sensors, and industrial automation. The content published on this platform is based on field experience, technical documentation analysis, and real-world system applications.

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Every article is carefully structured to deliver accurate technical knowledge, practical insights, and industry-relevant information aligned with modern automation standards.

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