[Al_The_Man]

This is where the subject gets muddy, as apart from the safety issues, there is at least two different philosophy's as to what or how grounding should occur, or as the PDF link I referenced before, what should be bonded to ground.
One is that all systems be bonded together to a common point and to earth ground in order to achieve a single point of reference that has effectively zero potential between them, this included all metallic objects of a system, shields and power supply commons.
The second is to effect electrical isolation between various POWER supply parts of the system in order to keep them as far apart electrically as possible.
Some manufacturers of equipment will often recommend one or other of the above methods.
I believe that in most cases, isolation is recommended because they are concerned that if the former is not carried out correctly, or variations are present, problems can occur.
A prime example is a PC power supply, there may be three user, two with a table or tower PC, and one with a laptop PC.
The first mentioned, may have a power supply which will be referenced to ground via the MB retaining screws, which is common to the service ground.
The second may have a M.B. which has insulated stand offs, disconnecting the PC supply from ground.
The Laptop PC power is usually above ground.
Unless steps are taken to make sure that the existing condition conforms to the selected method, then interference effects can occur.
As to the grounding/bonding of all power supply commons, Drive manufacturers such as A-M-C show the recommended method for either technique as a method of choice.
The key words are common bonding to ground, as the PDF shows.
Just as an example, I have been using the common bonding technique for many years, and often have gone against the manuf. recommended method of isolation in order to comply with the method I chose, which includes all power supplies made common to ground.
These PC based systems have been in place for many years now without any detrimental effects.
As to one philosophy or the other, apart from the manufacturers entreaties, there is no right or wrong.
You pick a method and carry it through correctly.
Al.