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Is it OK to put a disconnect between a VFD drive and the motor?

Published date: 24 April 2019

Is it OK to use a motor disconnect on the output of a VFD drive?

Product Line:
All open style and enclosed Altivar drives.

All models, All Serial numbers

Information not available in existing literature.

A disconnect can be used between the drive and the motor. This is general practice to assure that power does not reach the motor during maintenance and other non-operating times. Note that the disconnect should not be opened or closed while the VFD is running (outputting voltage from T1,T2,T3). This is sometimes referred to as "slamming the motor." This can damage the output IGBT components of the drive and such damage is not covered under warranty.  We recommend adding a fast-acting auxiliary contact on the disconnect that will trigger a freewheel stop on the drive before the main 3 phase contacts open. Refer to your drive's Programming Manual for instructions on programming a logic/digital input as freewheel stop. 

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