How to Fix Danfoss VLT Alarm 14 or AL14 Earth Fault?

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Staring at AL 14 on your Danfoss drive? Learn why this Earth Fault occurs, how to test your motor insulation, and the steps to clear the alarm safely.

 

How to Fix Danfoss VLT Alarm 14 or AL14 Earth Fault?

Solving Danfoss Alarm 14: The "Earth Fault" Troubleshooting Guide

If you are looking at your Danfoss VLT drive and the display is flashing AL 14, your drive is in "Survival Mode." In the Danfoss manual, this is defined as an Earth Fault.

In simple terms, the drive has detected that electricity is "leaking" out of its intended path and heading into the ground (earth). When this happens, the drive trips in microseconds to prevent the internal power transistors (IGBTs) from exploding. Let’s look at how to find the leak and get your system back online.

Common Causes of Alarm 14

When a Danfoss drive trips on AL 14, the problem is almost always in the field wiring or the motor. Here are the most likely culprits:

  • Motor Insulation Failure: The copper windings inside the motor have degraded and are touching the metal frame.
  • Damaged Motor Cable: The cable has been nicked, crushed, or heat-damaged, allowing a phase to touch the ground conduit.
  • Moisture in the Terminal Box: Water, condensation, or oil has entered the motor terminal box, creating a conductive path to the ground.
  • High Capacitive Leakage: You have very long motor cables (over 50-100 meters) which create "ghost" ground faults due to cable capacitance.
  • Internal Drive Failure: In rare cases, the drive’s internal current sensors or output stage have failed.

Step-by-Step Troubleshooting for AL 14

1. The "Isolation" Test (The #1 Maintenance Trick)

We need to figure out if the "leak" is inside the drive or out in the motor.

  • Power down the drive and wait for the display to go dark.
  • Disconnect the motor wires from terminals U, V, and W.
  • Power the drive back up and try to "Start" it (using Hand On mode) at a low frequency.
  • If AL 14 still appears: The drive's internal hardware is damaged. You likely need a new VFD.
  • If the drive runs fine without the motor: The VFD is healthy! The problem is 100% in your cables or the motor.

2. Inspect the Motor Terminal Box

If the drive passed the isolation test, it’s time to look at the motor:

  • Open the motor terminal box. Look for moisture, charred wires, or "carbon tracking" (black dust).
  • Clean and dry the box thoroughly with a heat gun or compressed air. Often, a damp terminal block is the only reason for an AL 14 trip.

3. The Megger Test (Insulation Check)

Use an insulation tester (Megger) to check the motor’s internal health.
Crucial Warning: Never use a Megger while the wires are still connected to the Danfoss drive! The high-voltage test signal will destroy the VFD instantly.

  • Disconnect the cables from the drive.
  • Check the resistance between each phase (U, V, W) and the ground.
  • A healthy motor should read several hundred Megohms. If it's near zero, your motor has a ground fault.

4. Check the RFI Filter Settings (Parameter 14-50)

If you are running on an "IT Grid" (isolated ground) or using very long cables, the drive's internal RFI filter might be causing nuisance trips.

  • Check Parameter 14-50 (RFI Filter).
  • In some specific power grids, turning the RFI filter OFF can clear intermittent AL 14 warnings caused by capacitive leakage. (Consult your plant electrician before doing this).

How to Reset Alarm 14

  1. Identify and fix the short circuit in the motor or cable.
  2. Press the [Reset] button on the Local Control Panel (LCP).
  3. Note: Alarm 14 is often a "Trip Lock." You may need to cycle the main power (Off/On) before the drive will allow you to reset the fault.

Summary

The Danfoss AL 14 alarm is a safety guardrail. It stops a small electrical leak from becoming a major fire hazard or hardware failure. Follow the Isolation Test first—it will tell you within 5 minutes if you need a mechanic to fix a motor or a technician to replace the drive.

 

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