On Fri, 15 Mar 2019 13:46:40 -0700, wrote:

Especially since
the VFD manual says to not connect anything across the output.
Switches and capacitors are specifically mentioned.

We have the VFD powering only the spindle motor, which requires 3
phase power from a single phase source. We have no filtering on the
VFD output. Everything else I previously mentioned is powered by
220VAC single phase, which is full of AC line filters. If you suspect
that the spindle power is somehow getting into the computah, perhaps
some shielding conduit might be an easy fix?

http://eecoonline.com/vfd-load-filters/
See comments under "VFD Load Filters".

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558