The power connector of the motor has a pin for grounding but it is not connected. However there is a tapped hole for grounding on the flange.

I guess the options for grounding are:
- Connect the gnd pin of the motor internally to the motor case. And that line goes to the drive's grounding input trough the power cable.
- Connect a single external grounding wire to the hole on the flange and connect other end to ... ? (fill in the ... please)