Assuming you are asking about mains power distribution, and not low-level DC power supplies:

Neutral and ground serve two different purposes. Neutral is the return for the mains hot wire; as such, it is a current-carrying conductor and must be sized appropriately. (It's worth noting that in a low-level circuit, such as what we deal with with microcontrollers and op-amps and the like, this circuit node would be called "ground.")

Ground is better called "safety ground," because it is NOT normally a current-carrying conductor, but rather it only carries current in the event of a fault (the hot lead shorted to a chassis). The ground wire must return to the panel and be connected to some sort of grounding system (cold-water pipe, copper rods buried in soil, building steel, or something that is dictated by local electrical codes). This is to establish a drain for the fault current as well as a "zero volt" node. At the main panel, the neutral must be bonded to the ground (and only at the main panel -- not in any sub-panels; however, again check your local codes). Bonding neutral to ground in this fashion forces the neutral node to be at 0 V with respect to ground, so the connected equipment doesn't float relative to ground.



What kind of system are you describing?



Power distro or otherwise?

-a