Frame ground vs. Electrical ground.

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