3-Phase Generator Frame Ground
It looks like you are using a 24VDC brushless DC motor as a generator, to stand in for a three-phase generator in some bench-top experiments.

If you are working with less than 50 volts, you should be able to operate this motor 'un grounded' without any safety concerns.

Regardless, best practice would be to earth the generator's "frame ground wire". Your electronics lab should have earth bars running around all the benches for this purpose.