One must ask the question right, to get the answer right :-)
At one time- not so long ago- it was the practice to "ground" the case of a range or clothes dryer by bonding it to the third wire- which also served as the "neutral" for any 110 loads the appliance might have had.
This is no longer allowed on NEW dryers and ranges, nor is it allowed to run NEW circuits this way. Section 250.140 is the place to start reading...
So, today, we no longer bond the case to the "neutral" wire. We run an additional wire to serve as the ground wire.
If an appliance has no 110v loads, then the third prong of the plug is a true "ground" prong.
