Service Replacement: Electrode Changes, Gas Bonding, and a Subpanel Wiring Shortcut
You are replacing a 200 A, 120/240 V residential service. Service-entrance conductors are 2/0 copper. The existing grounding electrode system consists of a driven ground rod and the metal water pipe, both landed at the meter base with 6 AWG copper. During the job the plumber replaces the water service with PEX, leaving only an 18 in. copper stub inside the foundation wall. The inspector also questions a 14 AWG copper conductor run to the new corrugated stainless steel gas piping. Meanwhile a helper has landed the shop subpanel's neutral and equipment ground on the same bar "to cut down on voltage drop." Final inspection is Thursday.
1. With the water service now PEX, what is the grounding electrode conductor requirement, and what must be done with the remaining copper water piping?
Read the worked answer
The water pipe is no longer a grounding electrode. A metal underground water pipe qualifies as an electrode only if it is in direct contact with the earth for 10 ft or more. With PEX serving the building and only an 18 in. stub inside the wall, the pipe fails that test. It must be removed from the electrode system conceptually - the GEC to it serves no purpose and should be relocated.
Driven rod only. With the rod as the sole electrode, the grounding electrode conductor is not required to be larger than 6 AWG copper. The existing 6 AWG is therefore compliant for the rod - the inspector's concern about "undersizing" does not apply here.
But the stub still needs bonding. The remaining copper water piping is a metallic piping system that may become energized, so it must be bonded to the service equipment. Bonding is not the same as grounding; it uses the equipment bonding rules, and 6 AWG copper is adequate for a 200 A service. Keep 6 AWG on the stub, landed on the grounding bar, and label it as a bonding jumper.
Also confirm: the rod connection is listed for direct burial and the clamp is accessible; the grounding electrode conductor is continuous or irreversibly spliced; and the water meter, if any remains, has a bonding jumper around it.
2. What is required for the gas piping bond, and is 14 AWG acceptable?
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14 AWG is not acceptable, and the reason is not just size.
- Size. Bonding of metal piping systems that may become energized is sized from the equipment grounding conductor table based on the overcurrent device protecting the circuit likely to energize the piping - here, the 200 A service. That gives 6 AWG copper. 14 AWG is roughly two sizes too small even before the CSST manufacturer's instructions are considered.
- Manufacturer's listing. Corrugated stainless steel tubing is not a grounding electrode and must never be used as one, but it does require bonding per the listing instructions, which for most listed CSST products specify a 6 AWG copper bonding conductor to the grounding electrode system, with a listed bonding clamp at the prescribed location. Manufacturer's instructions are part of the listing, so they are enforceable.
- Termination. The clamp must be listed for the purpose and the conductor must land on the grounding bar, not on the neutral bar, and not on a randomly chosen cold-water line.
Correct scope: remove the 14 AWG, install a listed CSST bonding clamp and 6 AWG copper to the service grounding bar, and photograph the installation before the wall closes. The gas bond is a life-safety item - an unbonded CSST system is a known lightning-related perforation risk.
3. The helper's neutral/ground connection at the shop subpanel needs to be corrected. Explain the fault and the correct configuration.
Read the worked answer
The fault: bonding the neutral and equipment ground at the subpanel creates a parallel return path for neutral current. Current divides between the feeder neutral and the equipment grounding conductor, the panel enclosure, the EMT, and anything bonded to it - water pipe, gas pipe, appliance frames. That produces objectionable current on the grounding system, and it is one of the most common causes of low-level shock complaints and noisy data circuits in a house.
The subpanel is in this case a load-side panel of the same service, and the rule is the same either way: a neutral-to-ground connection exists only at the service disconnecting means, plus a separately derived system if one exists. Nowhere else.
Correct configuration:
- Remove the green bonding screw or strap at the subpanel and remove the neutral-to-ground jumper.
- Land the feeder's equipment grounding conductor on the grounding bar, and land the neutral on the isolated neutral bar. Check that the neutral bar is not factory-bonded to the enclosure.
- Keep the feeder's neutral and equipment ground as separate conductors back to the main panel.
- Megger or ohmmeter check the completed work with the main off: no continuity should exist between the neutral bar and the panel enclosure except through the feeder back at the main.
This is a fifteen-minute correction with a torque screwdriver. Do it before Thursday, and verify every other subpanel your crew has touched in this house.