What can cause an OCL fault on ATV21 or ATV212 drives, and how can it be troubleshot?

An OCL fault indicates an output short-circuit condition. Possible causes include a phase-to-phase short circuit, a problem with the motor or motor cables, or low insulation resistance between the motor circuit and ground.

Follow these steps to help isolate the source of the OCL fault:

1. Inspect the motor and motor cables

   • Power down the drive and follow the appropriate electrical safety procedures.
   • Disconnect the motor leads from the drive.
   • Inspect the motor and wiring for damaged insulation, loose connections, or evidence of a short circuit.
   • Perform the appropriate insulation-resistance tests on the motor and motor cables to check for phase-to-phase or phase-to-ground insulation problems. Follow the motor manufacturer's recommended test voltage and procedure.

2. Determine whether the fault is associated with the motor circuit

   • If the motor and cables test correctly, the drive can be tested without the motor connected to help determine whether the OCL fault is coming from the drive.
   • Turn off the drive and wait for the DC bus to fully discharge before disconnecting or working on the output terminals.
   • Set F605 (Output Phase Loss detection) = 0 and F307 = 2 as required for the no-load test.
   • With the motor disconnected, run the drive at approximately 20 Hz, 40 Hz, and 60 Hz.
   • Measure the output voltage at each frequency and verify that the phase-to-phase output voltages are balanced and increase appropriately with frequency.

Safety note: VFD output terminals can contain hazardous voltage. Output-voltage measurements should only be performed by qualified personnel using appropriately rated equipment and the required electrical safety procedures.