Servo drives and RCDs

This is something I've never noticed being posted on any forums, but do Servo drives suffer from the same earth leakage issues as VFDs?

I'm just planning out the major electrics for the mill, and as I'm running the spindle using a VFD, and there is already one VFD and a DC drive on the RCD which if ran at the same time already trip it, I'm looking to run the new VFD through an isolating transformer to alleviate the issue.

However it got me thinking about the planned AC servo drives, and if they have any earth leakage, as VFDs and Servo drives in my mind basically work on the same basis (AC comes in, it get's rectified to DC, then the DC is used to create AC) just that Servo drives have a lot more control technology in them.

A quick google certainly turned up nothing, which then makes me wonder why can't VFDs be designed to minimise earth leakage?