A2021 START ENABLE 1 MISSING Alarm in ABB ACS550 Drive

A2021 START ENABLE 1 MISSING in the ABB ACS550 Drive indicates that the drive has not received the required Start Enable 1 signal. The ACS550 requires a valid Start Enable 1 command before it will allow the motor to start. If this signal is missing, the drive generates Alarm A2021 and inhibits motor operation until the enable signal is restored.

A2021 START ENABLE 1 MISSING Alarm in ABB ACS550 Drive


This alarm generally indicates a problem with the start enable signal source, digital input wiring, or fieldbus communication, rather than the motor or power circuit.

Possible Causes

  • Start Enable 1 signal is not present.
  • Incorrect Parameter 1608 – START ENABLE 1 setting.
  • Digital input wiring fault.
  • Loose or damaged input terminals.
  • Incorrect PLC or external control logic.
  • Missing fieldbus control word.
  • Fieldbus communication failure.
  • Incorrect I/O configuration.
  • Faulty digital input circuit.
  • External safety or interlock circuit open.

Solutions

  1. Check Parameter 1608 – START ENABLE 1 settings.
  2. Verify that the Start Enable 1 signal is present.
  3. Check the digital input connections and wiring.
  4. Inspect input terminals for loose or damaged connections.
  5. Verify PLC or external controller logic.
  6. Check fieldbus communication settings.
  7. Confirm that the fieldbus control word is sending the Start Enable command.
  8. Restore the missing enable signal.
  9. Reset the alarm if necessary and restart the drive.

Additional Information

The ABB ACS550 requires a valid Start Enable 1 signal before accepting a run command.

Alarm A2021 is generated when the drive does not detect this required enable signal.

According to ABB, the recommended corrective actions are to:

  • Check Parameter 1608 – START ENABLE 1.
  • Verify the digital input connections.
  • Check the fieldbus communication settings if the drive is controlled over a network.

Unlike a Run Command Missing alarm, A2021 specifically indicates that the Start Enable 1 permission has not been received.

Common Symptoms

  • Drive displays A2021 START ENABLE 1 MISSING.
  • Motor will not start.
  • Run command is ignored.
  • Drive remains in a ready state.
  • Alarm appears immediately after a start command.
  • PLC-controlled systems fail to enable the drive.
  • Fieldbus-controlled drives do not respond to start commands.
  • No output frequency is generated.
  • Alarm clears when the enable signal is restored.
  • Drive operates normally after correcting the enable source.

Recommended Troubleshooting Sequence

  1. Verify that the alarm is A2021 START ENABLE 1 MISSING.
  2. Check Parameter 1608 – START ENABLE 1.
  3. Verify the selected Start Enable signal source.
  4. Inspect digital input wiring and terminals.
  5. Confirm that the external Start Enable signal is active.
  6. Check PLC or relay logic if applicable.
  7. Verify fieldbus communication status.
  8. Confirm that the fieldbus control word includes the Start Enable command.
  9. Restore the enable signal.
  10. Restart the drive and verify normal operation.

A2021 START ENABLE 1 MISSING Check Table

Check PointAction
Parameter 1608Verify START ENABLE 1 setting
Start Enable signalConfirm signal is present
Digital inputsInspect wiring and terminals
External control circuitVerify PLC or relay logic
Fieldbus communicationCheck network status and settings
Control wordConfirm Start Enable bit is active
Drive operationVerify normal start after correction
Alarm statusEnsure alarm clears when enable is restored

Preventive Maintenance Tips

  • Verify Parameter 1608 during commissioning.
  • Periodically inspect digital input wiring and terminals.
  • Keep control terminals clean and securely tightened.
  • Test external interlocks and enable circuits regularly.
  • Monitor PLC and fieldbus communication for faults.
  • Verify I/O configuration after firmware or parameter changes.
  • Record recurring A2021 alarms to identify intermittent wiring or communication issues.
  • Follow ABB preventive maintenance recommendations.

Proper inspection of Parameter 1608 – START ENABLE 1, digital input connections, external control logic, and fieldbus communication settings will help prevent recurring A2021 START ENABLE 1 MISSING alarms in ABB ACS550 drives, ensuring reliable start authorization and normal drive operation.

Comments

Post a Comment

Popular posts from this blog

Allen Bradley Kinetix 5500 Drive Fault Codes List

Complete guide to Allen Bradley Kinetix 5500 fault codes. Troubleshoot FLT codes, Single-Cable (DSL) feedback errors, shared bus faults, and perform diagnostics via Studio 5000. Kinetix 5500 Fault Codes Reference Table Kinetix 5500 Fault Codes Reference Table Kinetix 5500 Fault Codes Reference Table Fault Code and Meaning Cause and Remedy FLT S03 – MTR OVERSPEED FL Motor Overspeed Factory Limit Fault Cause: Motor speed has exceeded 125% of its maximum speed. Remedy: Check control loop tuning. FLT S04 – MTR OVERSPEED UL Motor Overspeed User Limit Fault Cause: Motor speed has exceeded motor overspeed user limit. Remedy: Check control loop tuning. Increase the Motor Overspeed UL attribute value. FLT S05 – MTR OVERTEMP FL Motor Overtemperature Factory Limit Fault Cause: Calculations based ...
Read more

Danfoss VACON 100 FLOW Drive Fault Codes List

Access the complete reference guide for Danfoss VACON 100 FLOW drive fault codes. Learn to diagnose Multipump communication errors, dry run faults, and use Vacon Live software. VACON 100 FLOW Fault Codes Reference Table VACON 100 FLOW Faults and Alarms VACON 100 FLOW - Fault Tracing Fault Code and Meaning Cause and Remedy Fault Code 1, ID 1 Overcurrent (Hardware Fault) Cause: There is too high a current (> 4 × IH) in the motor cable. a sudden heavy load increase a short circuit in the motor cables the motor is not the correct type the parameter settings are not properly made Remedy: Check the loading. Check the motor. Check the cables and connections. Make an identification run. Set the acceleration time longer (P3.4.1.2 and P3.4.2.2). Fault Code 1, ID 2 Overcurrent (Software Fault...
Read more

ABB ACH580 Drive Fault Codes List

Access the complete reference guide for ABB ACH580 HVAC drive fault codes. Learn to diagnose issues via the Hand-Off-Auto panel, BACnet integration, and Fireman’s Override. The ABB ACH580 is the industry-standard flagship drive for HVACR applications. Designed to control air handling units, cooling towers, and chillers, it ensures critical comfort and safety in buildings. When a malfunction occurs, the dedicated Hand-Off-Auto (HOA) control panel displays a 4-digit code alongside plain-text diagnostics, often integrated directly into the Building Management System (BMS). This guide provides the most updated reference to help you interpret these codes and maintain building environmental standards. ACH580 Fault Codes Reference Table Use the search bar below or browse the table to identify your specific error code: ABB ACH580 Drive Fault Codes List ABB ACH580 Drive Fault Codes List Fault Code and Meaning Cause and Remedy A2B1...
Read more