This is not a 50 Hz 60Hz install which can work with what you are saying, and is definitely not a preferred method my be 50 years ago
You have not done many if any of these High frequency Spindle installs or you would not be posting this, while the spindle is running Rotor Voltage and Frequency, travels through the Ground conductor , unshielded Ground wire will cause unwanted noise if it is independent, So this is a No for all new installs of the High Frequency Spindles