[MML102783]

When using a VFD in the system they are very noisy, they are Grounded, Both the VFD and the Motor/Spindle, the Ground will have a lot of nasty spikes and voltage, that can mess up your DC supply if it is included with your star Ground

Your Power supply's are Grounded, and Isolated some have double Isolation, so have no problem not being part of the Ac 120/240v supply, Yes it's called floating in a good way, when not connected to Star Ground

I agree with Al with what he is saying, but when you add a VFD to the System that is when you can have problems with what is called Common Mode Voltage ( CMV ) this will occur on all VFD driven Motors and is really bad the higher the Frequency goes, 50Hz 60Hz not to bad, and is easy to deal with, the Spindles you will be running are 300Hz and 400Hz so create lots of noise on the VFD and Motor Ground, that can/will feed back into the DC supply if it is connected

The latest VFD Drives there switching frequency is higher than it used to be, creating even more Common Mode Voltage in the driven Motors, this all goes to Ground

Do you mean it returns to the electrical source via a grounded conductor? It does not truly travel to earth, unless the spike was lightning.

[mactec54]

Do you mean it returns to the electrical source via a grounded conductor? It does not truly travel to earth, unless the spike was lightning.

A Grounding conductor is for safety should never be used for anything else other than a safety Ground

No when using a dc power supply you have a + positive and a - Negative ( Common ) a dc Power supply the Common must return to the ( source ) dc supply to complete the circuit, then it can be Grounded to Earth Ground conductor in special circumstances, dc supplies are Grounded normally with the input AC power supply

There are some people that connect the dc common direct to Earth Ground, when using a dc supply this can cause problems even though they say it does not, the main problem is noise on the Ac Earth Ground which can affect the low voltage dc supply

In the case of a lightning spike connected this way could take out all the low voltage components

[Al_The_Man]

Do you mean it returns to the electrical source via a grounded conductor? It does not truly travel to earth, unless the spike was lightning.

The AC service supply has a grounded neutral at the supply transformer, so any power conductor connected to this supply is referenced to earth ground, which means that any current connection/leakage of the power conductor to earth results in a electrical circuit back to the source, i.e. through ground to the earthed supply point.
Once upon a time, rural telephone systems used the ground for the return path in order to save cost of using two conductors.
Any isolated supply that you chose to make one side common to earth ground uses the same return path to the grounded conductor source.
I have made it a practice throughout my career to earth ground all supply systems whether AC or DC, with no ill effects.
There have been a few past posts here where those that have had spurious e-stops problems have cured the issue by grounding the power common

A -ve charged lightening storm cloud has a equally +ve charged area in the ground that follows the storm cloud as it travels.

[mactec54]

The AC service supply has a grounded neutral at the supply transformer, so any power conductor connected to this supply is referenced to earth ground, which means that any current connection/leakage of the power conductor to earth results in a electrical circuit back to the source, i.e. through ground to the earthed supply point.
Once upon a time, rural telephone systems used the ground for the return path in order to save cost of using two conductors.
Any isolated supply that you chose to make one side common to earth ground uses the same return path to the grounded conductor source.
I have made it a practice throughout my career to earth ground all supply systems whether AC or DC, with no ill effects.
There have been a few past posts here where those that have had spurious e-stops problems have cured the issue by grounding the power common

A -ve charged lightening storm cloud has a equally +ve charged area in the ground that follows the storm cloud as it travels.

Good PDF but very old publication Note it states that the common of a DC supply must return to the source, it can then go to Ground if you chose, not to have the DC supply floating, your method is problematic, if you have a VFD Drive in the same system as Ground then has a lot of noise which will mess with the low voltage system, and all most everyone use's a VFD Drive in there system