Size for ground wires

[Al_The_Man]

Most supplies have a grounded neutral, so the DC negative wouldn't appreciate being grounded, you'd pop the breakers and possibly damage the PFC / rectifier. Not something to try!

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Every DC supply I have ever used or built was isolated from the AC supply, they are either 50hz/60hz transformer and bridge etc, or SMPS, all typically isolated.
Therefore in all the above examples, there is no problem earth grounding the DC supply common.
Of course, in order to do this, the transformer secondary itself cannot be, and is usually not, grounded, this allows the DC common to be.
A good example is a tower or desk top PC, the power common is connected to earth GND via the screws securing the MB that are through the board ground plane to the earthed chassis.
where the service ground is also terminated.
Al.

[wizard]

When did you last check the electrical code for this, I think you will find that it is not recommended, ( Old methods don't apply anymore ) DC Negative is never floating it is the return path if you want extra noise /voltage on your Grounds then it's your choice how you want to terminate it but the electrical code says different

Din Rail Grounding is completely to Code and can be more affective than what you are suggesting

Din Rail grounding maybe to code but that doesn’t mean that it is wise! There is huge variability in the quality of the din rail grounding systems I’ve seen. Combine that with the way some builders splatter those grounding blocks all over the panel and you end up defeating the concept of a star ground. Being code approved and inspiring confidence are two different things.

As for the comment on DC supplies I’m not sure if we are on the same page there.