First make sure the AC secondary side of the toroid is not at ground, (probably not), but it pays to check if grounding the DC-ve side.
I use this method all the time with Advanced Motion drives, and in fact the AMC site has a Technical Section where they describe this.
The drive signal common and the DC power common should have a bonding connection to a common Earth ground plate, this is a point set up for all the connections that are set up to Earth potential, including the service ground.
The PC power supply common should also be bonded to this point.
Al.
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.