In article ,
larry g wrote:
.......
difference. The motors that we fried were running 24x7 and would only last
a month or two before failing so in limited machine tool use it should not
be a problem.

I am curious; What voltage were these motor running on??
Someone reported that normal 230V motors seem to hold up well running
from a VFD, but higher voltage motors do not. So I am curious
if your failures support of disprove this theory.
chuck