Re: residental grounding
If I may throw in a little plain ol' English:
Bonding is effectively tying conductive parts to one another to minimize the possibility of voltage differences between the parts, whether this results in the parts being at zero volts to earth or not.
Grounding is effectively tying those parts to earth, with as low a resistance as possible, to minimize the possibility of voltage differences between parts as mentioned above, and the surrounding earth.
A grounding electrode does more to keep the earth around electrical equipment at the same potential as that equipment, than it does to keep the equipment itself at the system's neutral voltage (zero, hopefully).
The main bonding jumper is where the neutral and equipment grounding conductor(s) are tied together. This is the pathway through which any line-to-ground (as in metallic equipment, conduit, etc.) fault has a low-enough resistance to trip a breaker or fuse.
Bottom line: the earth alone is never called upon to be part of that fault-current pathway. The system neutral is the point toward which "return current" attemps to flow. The neutral being grounded is why the earth seems to behave similarly to neutral.
Some say that having a grounded system causes more danger than it circumvents, because a non-grounded system theoretically reduces likelihood of shock, but it also minimized gross system over-voltages from, say, lightning or primary-to-secondary faults.
[ December 14, 2005, 09:17 PM: Message edited by: LarryFine ]