Learn how to diagnose and reset Alarm 60 (External Interlock) on Danfoss VLT drives. This guide covers digital input settings, wiring checks, and parameter configurations.
Danfoss VLT Alarm 60 or AL60 indicates External Interlock. This means a digital input configured as an “External Interlock” has been deactivated.
Danfoss VLT Guide: Alarm 60 (External Interlock)
ALARM 60
Description: External Interlock
On a Danfoss VLT drive, Alarm 60 indicates that a digital input configured as an “External Interlock” has been deactivated. This is a safety or process feature used to prevent the drive from running unless a specific external condition is met.
Failsafe Logic: The External Interlock function typically uses Normally Closed (NC) logic. This means the drive requires a continuous 24V DC signal to a digital input to run. If the circuit opens (wire breaks or switch opens), the drive trips on Alarm 60.
Common Scenarios for A60
- Safety Devices: Fire alarm relays, emergency stop buttons, or pull-cord switches are open.
- Process Interlocks: A damper limit switch, a flow switch, or a vibration sensor has tripped.
- Broken Wiring: A loose wire or a broken conductor in the interlock loop back to the drive’s control terminals.
- Incorrect Programming: A digital input is programmed as an interlock but nothing is wired to it.
Troubleshooting Steps
1. Identify the Assigned Input
Check the programming in Parameter Group 5-1* (Digital Inputs). Look for any digital input that is set to [7] External Interlock.
2. Check the Status of the Input
Go to Parameter for Digital Input on the LCP display. This shows the status of the inputs in binary. Verify if the terminal assigned as the interlock is receiving 24V.
3. Inspect the External Circuit
If the input is ‘0’, trace the wiring from the drive terminal through your external switches and back to the 24V source. Look for open contacts or loose screws.
4. Temporary Bypass (For Testing ONLY)
To confirm the drive is healthy, you can temporarily place a jumper wire between Terminal 12 (+24V) and the assigned interlock terminal. If Alarm 60 clears, the fault is definitely in your external field wiring.
Important Parameters
| Parameter Name | Common Value |
|---|---|
| Terminal for Digital Input | External Interlock |
| Digital Input Status | Binary Readout |