Upgrading to 400 amp service. Have already set my two grounding rods and ran #2 solid for them.

My question is about the water bonding.

Existing water bond was (to my understanding) done wrong...but not noticed on inspection. It was attached to a hose bib on the opposite side of the house (60') from where the pipe enters the ground. At the time the whole house was copper piping.

Piping now changes to pex just AFTER it enters the house, so I am assuming that it does actually still need bonded...

That being the case...What size wire for the 30' run from the panel to the closest qualifying bonding point?

Water main is metallic and will remain so.

  • 3
    You may want to double-check with your jurisdiction (electrical permit or building permit department). Some places are still doing the water pipe bond, some have switched to only ground rods due to the prevalence of PEX, etc. May 23, 2023 at 19:35
  • 1
    Is your water main still copper/metallic, or is that going to be changed to plastic as well? May 24, 2023 at 0:32
  • My mains are copper and will remain so.
    – Shawn G
    May 24, 2023 at 15:57
  • Also, the language seems to suggest that, because the pipe enters the building (even if its only 6"), I need to bond it. But, having consulted with my inspector, he said not to bother. No explanation for what seems (to me) like it would be an exception, just..."I wouldn't bother".
    – Shawn G
    May 24, 2023 at 16:02
  • Exactly what I thought might (50%) happen. Local practices have a lot to do with this. My guess is that new buildings are being built with the water main not metal, so rather than pick and choose based on each situation, they just established a local rule of "two ground rods, no water pipe". May 24, 2023 at 17:34

1 Answer 1


Size of Grounding Electrode Conductor feeding metal water piping entering a building is based on size of ungrounded Service Entrance conductors from Table 250.66.

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For a 400A Service I would expect you would need 400CU/600AL kcm service conductors so you would need 1/0 copper for the water pipe grounding electrode.

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  • Strange, I thought the revisions stated never larger than 2/0.
    – Shawn G
    May 24, 2023 at 15:56

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