Originally Posted by
Jim Luttrall
All metal piping systems (water, gas, air, etc.) should be bonded back to the building grounding electrode system. This does not provide grounding for the electrical system, it prevents the piping systems from being energized and hurting people. You want the overcurrent device to trip, and bonding makes this possible.
As far as the overcurrent device goes, it's the low impedance path back to the source that allows for sufficient current to flow to trip the breaker or blow the fuse.
The grounding electrode path is relatively high impedance and is mainly for high voltage events, like lightning, and to stabilize voltage.