250.68(C)(1) Grounding Electrode Conductor Connections. Interior metal water piping.
Code Change Summary: A revision was made to clarify which portion of interior metal water piping can be used to extend a grounding electrode conductor (GEC).
This code section must be read carefully and the gray shading shown in the first published edition of the 2017 NEC® does not appear to correctly highlight all of the code changes to this section.
Previous editions of the NEC® state that interior metal water piping located more than 5 feet from the point where the water pipe enters the building cannot be used as a common connection point to extend a GEC to a grounding electrode. It was assumed that this code section was speaking of interior metal water piping that was connected to a metal underground water pipe that qualifies as a grounding electrode in accordance with the requirements in 250.52(A)(1).
Basically, a metal underground water pipe in direct contact with the earth for at least 10 feet would turn up inside the building above slab as the water supply for the structure. The GEC must connect to the water pipe within the first 5 feet of the pipe after it emerges from underground. Connecting the GEC to the water pipe at a point greater than 5 feet from where the piping enters the building was a code violation.
Bonding water piping systems is different than using the water pipe as an actual grounding electrode. Sometimes, metal water piping serving a building may not be in contact with the earth for 10 feet or more and does not qualify as a grounding electrode. The water piping still needs to be bonded per 250.104(A). This bonding can be done anywhere along the metal water piping system and is not required to be done within the first 5 feet where the piping system enters the building.
The revised code language now makes it clear that interior metal water piping used to extend the GEC connection to a metal underground water pipe electrode must be electrically continuous with the metal underground water pipe.
Below is a preview of Article 250. See the actual NEC® text at NFPA.ORG for the complete code section. Once there, click on their link to free access to the 2017 NEC® edition of NFPA 70.
2014 Code Language:
250.68(C) Grounding Electrode Connections.
(1) Interior metal water piping located not more than 1.52 m (5 ft) from the point of entrance to the building shall be permitted to be used as a conductor to interconnect electrodes that are part of the grounding electrode system.
2017 Code Language:
250.68(C) Grounding Electrode Conductor Connections.
(1) Interior metal water piping that is electrically continuous with a metal underground water pipe electrode and is located not more than 1.52 m (5 ft) from the point of entrance to the building shall be permitted to extend the connection to an electrode(s). Interior metal water piping located more than 1.52 m (5 ft) from the point of entrance to the building shall not be used as a conductor to interconnect electrodes of the grounding electrode system.