Frame ground vs. Electrical ground.

[polaraligned]

Hi,
I have just got 3 Granite VSD-E drives and have a grounding
question. Here is a quote from their manual:

>>>>>
7.2 Grounding
Drive has two separate grounds for separate purposes which are named
as GND (ground) and FG (frame ground). GND is the electrical 0V
potential shared with power supplies and all connector pins labeled as
"GND". Connect GND to power supply 0V terminal.
FG is the ground for EMI shielding which is located in D-sub connector
metal shells and D-sub connector pins labeled as "FG". FG and GND are
electrically floating against each other but are connected by EMI
suppression capacitor inside drive. Make sure that D-sub shells make
electrical contact to enclosure metal and cable shields are connected
to FG through corresponding pins or D-sub shells.
>>>>>

I plan on installing the drives in the same metal cabinet with my
computer, BOB, power supply, etc. Just like I did on my last machine.

In the past I have connected all grounds to a common point inside the
metal cabinet. This point also was connected to the ground of my
mains AC power.

Do I really need to keep 2 separate grounds? Can I just tie FG and
GND together?

If I tie the drive FG to the metal enclosure, then what do I do
with the mains ground for safety reasons?

Thanks,

Scott

[Al_The_Man]

I cannot speak for Granite devices, but generally the term Frame Ground FG refers to the part of the device that comes in contact with the outer metallic case etc that would contact the enclosure or Service grounded point when mounted.
Other connections are named chassis ground, Logic Ground, Power common, and these may be isolated from the case or Frame ground, then it can be made optional as to whether these are tied to the FG.
There are basically two schools of thought or practices as to whether all systems are kept isolated from each other or tied together and connected to a common ground and machine bonding point.
Personnaly, I find it misleading and bad practice to call these other commons 'ground' when in fact they may not be at all at ground potential, and misleading, especially to those who are newcomers to electronics.
The bottom line is, you should only have one ground point set up that bonds the service ground to all the metalic points on the machine, together with the rest of your grounded commons and shields.
Al.

[Xerxes]

Thank you for contributing input Al!

Please see figure 12 in VSD-E manual. Power supply GND (0V line) should be connected to case (FG). So, do not leave GND and FG floating. Nothing will blow if this connection is not made, but may lead to worse EMI shielding.