6 Common Mistakes When Commissioning a VFD

 

Commissioning a Variable Frequency Drive (VFD) is one of the most important steps in making sure a machine runs smoothly, safely, and efficiently. But this is also the stage where small oversights often turn into costly downtime, nuisance faults, or even damaged equipment.

Here are some of the most common mistakes technicians and engineers run into during VFD commissioning—and how to avoid them.

1. Ignoring EMI Best Practices in Panel Design

Electromagnetic Interference (EMI) can sneak into control circuits and create hard-to-diagnose problems. For example, one packaging line would randomly fault out on encoder loss. The root cause? Motor cables and encoder feedback lines were routed side-by-side in the same tray, causing noise coupling.

Our Recommendation:

• Keep motor/power wiring physically separated from control and feedback wiring.

• Use shielded cables and terminate shields properly.

• Add reactors or filters if the manufacturer recommends them.

• Other examples for EMI mitigation here: 7 Steps to Reducing EMI with VFDs

Important: Account for Motor Cable Run Length

Think of a manufacturing facility experiencing multiple motors burning out within weeks of installation. Investigation revealed 300-foot cable runs without any output filtering. The reflected wave voltage spikes were stressing motor insulation far beyond its rating.

Our Recommendation:

• Stay within the drive manufacturer’s recommended cable length.
• For long runs, use dV/dT filters or reactors.
• Always check routing to minimize interference with control signals.

2. Miswired or Incorrectly Entered Motor Data

A common field mistake is forgetting to set motor jumpers from 460V to 230V or vice versa. One service call involved a motor that failed catastrophically at startup. The issue? The motor was wired for 230V while the drive was programmed for 460V.

Our Recommendation:

• Double-check jumper positions on the motor terminal block.
• Enter all motor nameplate values—voltage, current, frequency, RPM—correctly into the drive.
• For servo motors, ensure U/V/W phases are wired correctly.

3. Overlooking Brake Operation

A good example of the importance of proper brake operation is a crane or hoist application. If the motor brake didn’t open before attempting to ramp up to speed, the VFD could fault out on an overcurrent error, attempting to spin the motor while the brake is still engaged. In the reverse, if the brake did not engage quickly enough after the motor stopped spinning, a heavy load could drift causing a serious safety concern to equipment or personnel working nearby.

Our Recommendation:
Test the brake’s open and close timing thoroughly and adjust control signals or delays in the VFD to guarantee a safe handoff between brake and motor torque.

4. Forgetting About Regenerative Energy

A sawmill had constant drive overvoltage trips every time operators stopped the high-inertia saw quickly. The regenerative energy had nowhere to go, spiking the DC bus. Installing a braking resistor solved the problem immediately.

When you think of regenerated energy it is difficult to ignore elevator applications. When an empty car is ascending or when an elevator car is descending full of people the motor is generating energy. This situation will damage the VFD unless there is a properly sized braking resistor or line regen units like the ones below.

Our Recommendation:

• Use braking resistors when dealing with overhauling or high-inertia loads.
• For frequent regen, consider regenerative drives that feed energy back to the grid.

5. Starting the Machine Under Load

One pump station tried to commission with the motor fully coupled and under system pressure. The drive faulted immediately on startup, leading the crew to think the drive was defective. Once the motor was uncoupled and tested unloaded, the drive worked fine.

Our Recommendation:
Start with the motor unloaded (and ideally uncoupled). Verify rotation, data entry, and basic control before reconnecting to the machine.

6. Skipping Commissioning Steps

In a bottling line retrofit, engineers skipped the velocity tuning and went straight to position control to save time. As a result, the velocity loop was unstable, causing bottles to be misaligned on the conveyor. After going back to tune the velocity control first, the position control regained its accuracy. 

Our Recommendation:
Use this proven sequence for optimal VFD commissioning:

1. Start with open-loop V/Hz or (A)SCL control.
2. Run motor identification to build an accurate model. 
3. Verify encoder feedback and motor rotation.
4. Tune velocity before moving to positioning.
5. Ramp up slowly before full-speed, full-load testing.
6. Test manually with COMBIVIS 6 software before switching to PLC control.  

Quick Troubleshooting Checklist for VFD Commissioning

Before calling in outside support, run through this checklist to catch the most common problems:

• ✅ Are power and control cables routed separately and properly shielded?
• ✅ Is motor cable length within the drive manufacturer’s recommendations?
• ✅ Are motor leads wired in the correct sequence, and jumpers set for the correct voltage?
• ✅ Did you enter all motor nameplate data correctly (voltage, current, frequency, RPM)?
• ✅ Is the brake opening before torque is applied and closing safely after stopping?
• ✅ Have you accounted for regenerative energy (braking resistor or regen unit if needed)?
• ✅ Did you start the motor unloaded/uncoupled before connecting it to the machine?
• ✅ Did you run motor identification (auto-tune) and basic open-loop tests before closed-loop?
• ✅ Have you tested operation gradually (low speed, low load, conservative ramps) before full output?

Final Thoughts

Commissioning a VFD involves more than simply getting the motor to run. Each step is crucial for ensuring safe, efficient, and reliable long-term operation. The most common issues, such as noise, incorrect wiring, regenerative energy problems, or skipped tuning, are often preventable if they are addressed early. Taking the time to be patient and detail-oriented during the commissioning process will lead to fewer headaches, improved uptime, and a system that operates precisely as intended.