Variable Frequency Drive Noise Reduction

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Ground straps that are made up of very fine braided wires can have the opposite results relative to high frequency (and expectations they work). It may appear they are all shorted together, but typically they have oxide, and oil film that insulates them. So these tiny wires with the RF skin depth makes this look like a large impedance. That is the same issue with stranded 12AWG SO cord ground.
Your solid strap is the way to go. Should be interesting with installing motor leads in a coaxial Faraday shield. The only design issue is how to connect this shield with minimal inductance. Typical STP with ground drains (pigtails), will have around 25ohm impedance per inch at 100MHz (22AWG STP signal wire and drain wire gauge).
There probably is some conducted emissions on the 220VAC power to the VFD. I don't know how good the EMI front end filters are in the VFD.
It looks like you fixed your EMC issue.
Very nice write up that should be helpful to many.