VFD Faults: What Your Drive Is Trying to Tell You

The pump stops.

The variable frequency drive shows a fault.

Someone presses RESET.

The system starts again.

A week later, it happens again.

Repeated VFD faults should not become part of normal operation.

The fault code exists because the drive detected a condition outside its expected operating range. Depending on the drive, fault categories can include overcurrent, overvoltage, undervoltage, phase loss, overheating and motor overload. ABB and Danfoss drive documentation both identify these types of conditions in their troubleshooting guidance.

What Do Common VFD Faults Mean?

The specific code and troubleshooting procedure depend on the VFD manufacturer and model.

Always use the documentation for the installed drive.

But understanding the general categories can help facility teams capture better information before service arrives.

Overcurrent

An overcurrent fault means the drive detected current beyond its permitted condition.

Potential causes can include a motor or driven-equipment problem, rapid acceleration, wiring issues or excessive load.

Danfoss specifically recommends checking the application when an overcurrent condition occurs.

For a pump application, look beyond the VFD.

What was the pump doing when the fault occurred?

Was a valve moved?

Did something obstruct the pump?

Did the motor or equipment suddenly become harder to turn?

The drive may be reporting the symptom of a mechanical problem.

Overvoltage

A DC-link overvoltage fault indicates voltage inside the drive has risen beyond its permitted limit.

Depending on the application, this can be associated with supply conditions or energy returning from the motor during deceleration.

Drive-specific troubleshooting guidance may include checking incoming voltage and reviewing deceleration settings.

Do not change parameters randomly.

Understand why the fault occurred first.

Undervoltage

Undervoltage means the drive is seeing insufficient DC-link voltage.

That can point toward issues with incoming power, supply interruptions or other electrical conditions.

ABB and Danfoss both identify DC-link undervoltage as a distinct fault or warning condition.

If several pieces of equipment experience problems at the same time, that context can be especially useful.

Phase Loss

A VFD may detect a missing input or output phase depending on the drive and fault.

This can point toward electrical supply, wiring, connection or motor-circuit problems.

Do not continually reset a phase-related fault.

The electrical condition needs to be checked.

Drive Overtemperature

Variable frequency drives need cooling too.

Fans, heatsinks and ventilation paths help remove the heat generated by the drive.

Dust, restricted airflow and high ambient temperatures can reduce cooling.

ABB warns that dirty heatsinks can contribute to overtemperature warnings and faults in its drive hardware documentation.

That makes summer a particularly useful time to inspect drive ventilation.

Motor Overload or Temperature

Some drives provide motor thermal protection based on configured motor data and operating conditions.

If a motor overload or temperature fault appears, check the motor as well as the drive.

Danfoss troubleshooting guidance recommends looking at motor overheating, mechanical overload and configured motor-current data when motor thermal faults occur.

What Should You Do When VFD Faults Occur?

Before pressing reset, record what happened.

Take a photo of the display.

Write down:

• Fault code

• Date and time

• Pump or motor involved

• Operating speed

• Motor current if available

• What the equipment was doing

• Whether another alarm occurred

• Whether the fault happens repeatedly

This information can drastically improve troubleshooting.

Look at the Fault History

Many drives retain recent fault information.

Use it.

ABB's troubleshooting documentation specifically references reviewing stored error logs as part of fault diagnosis.

One fault can be an event.

Five identical faults at approximately the same load or time can be a pattern.

Patterns are much more useful.

Don't Treat Reset as Repair

A reset tells the drive to try again.

It does not tighten an electrical connection.

It does not clear an obstructed pump.

It does not improve ventilation.

It does not correct low incoming voltage.

And it does not repair a motor.

If the same VFD faults keep returning, the equipment is providing information that should be investigated.

The Drive May Be Protecting Something More Expensive

A VFD fault can be frustrating because it stops equipment.

But that shutdown may also be preventing a motor, pump or drive from continuing to operate under damaging conditions.

Instead of asking only, "How do we clear the fault?" ask:

"Why did the drive decide it needed to stop?"

Academy Pump & Motor provides pump, electric motor and system troubleshooting throughout Calgary and surrounding areas.

If your equipment is experiencing repeated VFD faults, capture the code and operating conditions before resetting the system.

Call Academy Pump & Motor at 403-437-7888 or visit academypump.ca.