You can use the grounded circuit conductor to ground (bond) the non-current carrying parts of equipment (and raceways and other enclosures) at certain locations [see NEC Sec. 250.142]. In many (but not all) wiring systems, this would be the neutral conductor.
On the supply side, the grounding point must be within the enclosure of the:
- AC service-disconnecting means, or
- Main disconnecting means for separate buildings as provided in Sec. 250.32(B), or