ThinkGood,
section V of art 250 addresses 'bonding' , some codes that come to mind per the original post:
250.104(A)(2) Buildings of Multiple Occupancy. In buildings of multiple occupancy where the metal water piping system(s) installed in or attached to a building or structure for the individual occupancies is metallically isolated from all other occupancies by use of nonmetallic water piping, the metal water piping system(s) for each occupancy shall be permitted to be bonded to the equipment grounding terminal of the panelboard or switchboard enclosure (other than service equipment) supplying that occupancy. The bonding jumper shall be sized in accordance with Table 250.122.
commentary.....
The intent of 250.104(A)(2) is to recognize that the increased use of nonmetallic water piping mains causes the interior metal piping system of a multiple-occupancy building to be isolated from ground. Therefore, the water pipe is permitted to be bonded to the panelboard that serves only that particular occupancy. The bonding jumper, in this case, is permitted to be sized according to Table 250.122, based on the size of the main overcurrent device supplying the occupancy.
250.104(B) Other Metal Piping. Where installed in or attached to a building or structure, metal piping system(s), including gas piping, that may become energized shall be bonded to the service equipment enclosure, the grounded conductor at the service, the grounding electrode conductor where of sufficient size, or to the one or more grounding electrodes used. The bonding jumper(s) shall be sized in accordance with 250.122 using the rating of the circuit that may energize the piping system(s). The equipment grounding conductor for the circuit that may energize the piping shall be permitted to serve as the bonding means. The points of attachment of the bonding jumper(s) shall be accessible.
FPN:Bonding all piping and metal air ducts within the premises will provide additional safety.
commentary....
Section 250.104(B) was revised for the 2002 Code to state that gas piping is treated exactly the same as all "other metal piping" systems within a building
