Question about power supplies and ground

[kae]

This question may seem dumb to some but I don't know the answer.

I am building a 56 volt unregulated power supply to run the steppers on my recently converted square column mill. I am using a recycled computer power supply to power the BOB and the cooling fans on the heat sinks for the Geckos. I realized while assembling the computer power supply into the driver cabinet (I disassembled the PS and mounted the PCB onto standoffs) that the black common wires go to earth ground. If you check with a meter, you get a circuit between the case and the black wires. The corner mount traces on the PCB that makes up the power supply connect to the black common wires. Probably no mystery here.
Now, here is my question. Why does the unregulated supply I am building to drive the steppers not go to an earth ground on the common side?

Just curious for an answer. Thanks.

[Al_The_Man]

Mainly a question of preference, either personal or abiding by a certain manufacturer or supplier of drives.
Some recommend complete isolation of all P.S. this may isolate all DC supplies but it does not always isolate AC induced/coupled signals.
I tend to follow the common ground approach but is should be done in a proper manner by setting up a common ground point that includes the system ground conductor and any Gnd bonding conductors from metallic parts of the machine and motor frames etc, all power supply commons would also go to the common point as well as shields.
Al.

[kae]

So Al, if I understand you correctly, I can leave the stepper supply as is or I can take it to an earth ground. So far, the earth ground on my driver cabinet is the cabinet itself. How would you do it?

[Al_The_Man]

I believe Gecko specify an isolated ground so it is up to you.
I always ground my supplies to a common point in the cabinet or enclosure.
Where the ground plate is set up.
Al.

[kae]

Thanks, Al.