Do I Need To Bond To My Cold Water Pipe?
February 26, 2006
Q: I installed a feeder from my main service disconnect to a new sub panel in my home. The underground water pipe that supplies the home is plastic but, it is copper in the house. The copper water pipe is not underground and there is no metal water pipe in contact with the earth. Does the NEC allow the water pipe to be bonded to the feeder grounded circuit conductor in the feeder sub-panel because the water pipe is not being used as a grounding electrode?
A: The interior metal water pipes must be bonded to the grounding electrode system. The requirement for bonding the metal water pipe is found in 250.104(A)(1) and reads like this: “The metal water piping system shall be bonded as required in (1), (2), (3) or (4) of this section. The bonding jumper(s) shall be installed in accordance with 250.64(A), (B) and (E). The points of attachment of the bonding jumper(s) shall be accessible.”
Part (1) of 250.104(A) specifies which parts of the grounding electrode system are suitable for bonding the water pipe. They are the service equipment enclosure, the grounded conductor at the service, the grounding electrode conductor if it is large enough, or to the one or more grounding electrodes used.
The size of the bonding jumper cannot be smaller than shown in Table 250.66. For example, a 200A service that consists of 3-3/0 Type THWN conductors would require a 4 copper bonding conductor. If the grounding electrode conductor is 6 copper because the grounding electrode is two 8-foot ground rods, the bonding conductor from the water pipe would have to terminate on the service equipment enclosure, or the grounded circuit conductor (neutral) at the service.
This is because the bonding conductor is required to be larger than the service grounding electrode conductor.
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