Service Replacement With a Plastic Water Service Line
A 1968 single-family dwelling is getting a 200 A overhead service replacement. The service-entrance conductors are 3/0 Cu, and the utility has just replaced the water service line from the main to the house with plastic. Inside, the metallic water piping is continuous and includes the water heater and fixtures. The only other grounding electrode is an existing 8 ft × 5/8 in. copper-clad rod at the meter, connected with 6 AWG Cu. The homeowner wants to reuse the interior water pipe as the grounding electrode because it is "still metal" and asks you to connect the grounding electrode conductor to the pipe in the basement, about 18 ft from where it enters the building. You also notice the existing water meter has no bonding jumper and the panel's neutral and ground bars are separated. The inspector has not yet been called.
1. May the interior metal water pipe serve as the grounding electrode for this service? Explain what changed and what the pipe must be used for instead.
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No. A metal water pipe is a grounding electrode only where it has at least 10 ft of direct contact with the earth, as required by 250.52(A)(1). Once the utility replaces the service line with plastic, the interior piping no longer has that earth contact, so it cannot be the grounding electrode for the service. The pipe does not become irrelevant, however. Because it is a metallic water piping system likely to become energized, 250.104(A) requires it to be bonded to the service equipment or grounding electrode system. That bonding jumper must be sized from Table 250.66 using the 3/0 Cu service conductors, which calls for 4 AWG Cu. The connection can be made at an accessible location on the interior piping, not necessarily within 5 ft of entry, because this is bonding, not a grounding electrode conductor connection. The grounding electrode system must rely on the rod and any other qualifying electrode.
2. What electrode(s) and conductor sizes should be installed, and where should the connection be made?
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The existing 8 ft rod is a qualifying electrode under 250.52(A)(5) if it is listed and at least 5/8 in. diameter, or 1/2 in. if listed. The grounding electrode conductor to a rod need not be larger than 6 AWG Cu under 250.66(A), so the existing 6 AWG Cu is acceptable. But 250.53(A)(2) requires a rod electrode to be supplemented by another electrode unless it can be shown that the rod has 25 ohms or less resistance to earth. The practical answer is to drive a second rod and connect it to the first with a 6 AWG Cu bonding jumper. The water pipe bonding jumper should be 4 AWG Cu per Table 250.66 and should be connected to the metallic piping with a listed clamp. The grounding electrode conductor connection to the water pipe would have had to be within 5 ft of entry if the pipe were an electrode, but it is not; the connection here is a bonding jumper, so the basement location is acceptable if accessible.
3. Is the missing water-meter bonding jumper a violation, and does the neutral/ground separation in the panel affect the answer?
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Yes, the missing meter jumper is a defect. Where a water meter is removed for service, the metallic piping system can be interrupted, so 250.104(A) and 250.68(B) require a bonding jumper around the meter to maintain continuity of the bonding path. The jumper should be sized at least as large as the water-piping bonding jumper, 4 AWG Cu in this case. The neutral and ground bars being separated in the service panel is correct for a service panel only if the grounding electrode conductor and main bonding jumper are arranged so the service neutral is bonded to the enclosure and grounding electrode system at the service disconnect. The separation at a subpanel would be correct, but at the service it is not simply a matter of keeping them apart; the main bonding jumper must be installed at the service disconnect. The inspector will check both the electrode system and the main bonding jumper.