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What could be causing the motor coupling between my motor and compressor to break when the motor is powered with a VFD?

Issue:
What could be causing the motor coupling between my motor and compressor to break when the motor is powered with a VFD?

Product Line:
All VFD product lines

Environment:
All models, All serial numbers

Cause:
Motor coupling is breaking when powered by VFD.  Did not do this when connected to line power.

Resolution:
Check the motor control type (CTT parameter on most drives).  If this is in a sensorless flux vector or flux vector control mode, try changing to "v/f 2pts." mode or Standard mode.  These modes do not try to automatically adjust motor voltage to maintain torque.  

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