# ungrounded 480 delta and VFD



## scotch (Oct 17, 2013)

Follow the drive manufacturers instructions I guess !


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## micromind (Aug 11, 2007)

Most likely you'll need to disconnect the MOVs. Sometimes this is done by removing a jumper, sometimes you'll need to cut a jumper. 

If the MOVs are left in a circuit that is not a solidly grounded Y, they may very well see the high leg as a voltage spike, try to clamp it and since it's not a transient, they'll blow up.


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## JRaef (Mar 23, 2009)

Removing the MOV ground reference (if possible, many make it all but impossible) is one way, but it also removes some of the protection the MOVs provided and usually violates the UL listing of the VFD (i.e. the VFD was UL listed with it so removing it alters the product). AB drives for example give you nice easy jumpers to access the ground reference so that you can remove it, but in doing so, they warn you that the UL listing is void (most people don't notice that footnote).

The BEST way, if you have to live with a Delta power system, is to use a Delta-Wye Drive Isolation Transformer ahead of the drive. It creates an isolated grounded Wye feed for the VFD without compromising the reasons why someone wanted an ungrounded Delta system. A Drive isolation Transformer is one that is a shielded isolation transformer with a 1:1 ratio, but Delta primary, Wye secondary.


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## eddy current (Feb 28, 2009)

Check the specs of the drive. It may only accept a wye, void warranty.


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