Your most pressing National Electrical Code (NEC) questions answered
Q. Does the Code allow metal piping for the interconnection of other grounding electrodes?
A. Yes. Grounding electrode conductors and grounding electrode bonding jumpers are permitted to terminate to interior metal water piping located not more than 5 ft from the point of entrance to the building/structure [250.68(C)(1)].
An Exception follows this rule and states: In industrial, institutional, and commercial buildings where conditions of maintenance and supervision ensure only qualified persons service the installation, the entire length of the metal water piping system can be used for grounding purposes, provided the entire length, other than short sections passing through walls, floors, or ceilings, is exposed.