Troubleshooting ABB ACS880 Emergency Stop OFF2 (Fault 71B1)

A guide to understanding the Emergency Stop OFF2 condition on ABB ACS880 drives. Learn the difference between OFF1, OFF2, and OFF3, and how to troubleshoot Fault 71B1.

 

ABB ACS880: Emergency Stop OFF2

In the ABB ACS880 ecosystem, an "Emergency Stop OFF2" command is a safety or operational state that triggers an immediate Coast-to-Stop. When this command is received, the drive instantly stops firing the IGBTs (power transistors), disconnecting power from the motor and allowing it to spin down freely under its own inertia.

Fault Code: 71B1

Display Message: Emergency stop (OFF2)

Action: The drive trips and the motor coasts to a stop. The drive cannot be restarted until the signal is reset.

OFF2 vs. Other Stop Modes

Mode	Type	Action
OFF1	Normal Stop	Stops along the standard deceleration ramp.
OFF2	Emergency Ref	Coast to stop. Power is cut immediately.
OFF3	Emergency Stop	Emergency ramp stop (usually a faster, dedicated decel ramp).

Common Causes of Fault 71B1

• E-Stop Button Pressed: A physical emergency stop button wired to a Digital Input (assigned to OFF2) has been activated.
• Fieldbus Command: The PLC or control system sent an "OFF2" bit via the control word (e.g., Profinet or Ethernet/IP).
• Broken Wire: If the digital input assigned to the Emergency Stop is "Active Low" (failsafe), a broken wire or loose terminal will trigger the fault.
• Logic Configuration: Incorrect parameter settings in Group 21 or Group 31.

How to Troubleshoot & Reset

1. Check Physical E-Stops: Ensure all mushroom buttons are pulled out/reset.
2. Identify the Source: Check Parameter 31.11 (Fault Reset Selection) and Parameter 21.05 (Emergency Stop Source) to see which input is mapped to OFF2.
3. Monitor Digital Inputs: Use Parameter 10.01 (DI Status) to see if the assigned input is changing state when you toggle the switch.
4. Fieldbus Check: If controlled via PLC, check the Control Word bit 1. Bit 1 must be "1" for the drive to run; a "0" triggers OFF2.
5. Resetting: Once the signal is healthy, you must apply a Reset command (via panel or DI) before the drive will accept a new Start command.

NOTE: OFF2 is often used for "Emergency Coast" scenarios. If your application requires a controlled, high-speed stop, consider using OFF3 (Emergency Ramp) instead.

Related Parameters

• 21.04: Emergency stop mode (Defines if OFF1, OFF2, or OFF3 is used).
• 21.05: Emergency stop source (Defines which DI or bit triggers the stop).
• 31.11: Fault reset selection.