danfoss a60 alarm

In Danfoss VLT drive (such as the FC-102, FC-202, or FC-302), Alarm 60 (A60) stands for External Interlock. This alarm means the drive has been told to stop because a safety circuit or external device (connected to a digital input) has opened. The drive will not run until this circuit is closed again and the alarm is reset.

Common Causes & Troubleshooting

The "External Interlock" is essentially a "permission to run" signal. If the drive loses the 24V signal on the terminal assigned to this function, it trips.

• Open Safety Device: Check any external devices wired to the drive, such as:

  • Fire/Smoke detectors or Fire Alarms.

  • High/Low pressure switches.

  • Emergency Stop (E-Stop) buttons.

  • Freezestats (in HVAC applications).

• Loose Wiring: Check for loose or broken wires on the control terminals.

• Blown Fuse/Power Loss: If your 24V supply is shorted or failing, the drive won't see the signal and will trigger the alarm.

• Incorrect Programming: If you aren't using an external interlock but the drive is programmed to look for one, it will trip by default. 

How to Fix / Reset

1. Check the Safety Circuit: Ensure all external sensors are in their "normal" state. If a pressure switch has tripped, you must fix the mechanical issue first.

2. Verify Voltage: Use a multimeter to check for 24V DC between the Common (Terminal 12) and the Interlock Input.

   • Note: If you are testing and want to bypass this for troubleshooting, you can install a temporary jumper wire between 24V and digital input.

3. Clear the Alarm: Once the 24V signal is restored, press the [Reset] button on the drive keypad (LCP).