Servo Drive Leakage Current

I would like to discuss leakage current of Servo Drives and see if anyone else out there has had the same issues. We are a manufacturer, with our own engineering team, that builds machines to be used in our production facility. We follow all standards for testing of equipment such as ground bond, hi pot, insulation resistance and leakage current tests before a machine is released into production.

Most recently we have had issues with Servo drives leakage current to ground above 30ma. Talking with our vendors and manufacturers and also doing research on our own we have tried a number of items to try and reduce the leakage current to below 5ma of which is our standard.

We have tried different filters, isolation transformer with separate ground, moved servo drives to their own cabinet to keep the wire separated from
the rest of our control system. This has helped but never lowered the current to below 5ma as mentioned above.

Is anyone else having the same issues? Is there something we can do that perhaps we are missing?