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In California, my 200A main service panel is grounded with CEE. Within the same structure this main panel serves a 200A subpanel (including ground conductor) in the garage. The garage subpanel serves a 100A subpanel (including ground conductor) in a utility room on the opposite corner of the house from the main panel. Thus all panels are grounded together. Ground is bonded to neutral only at the main service panel.

The utility room panel is within easy distance of a major copper water pipe and major iron gas pipe, both coming from burial in earth or concrete.

When am I required to bond my ground to a water pipe? A gas pipe?

When should I bond my ground to a water pipe or gas pipe?

Is there a risk in bonding in multiple places?

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  • I'm not sure there is a bond to my gas pipe, but the water pipe ground connection is right where the supply enters the house.
    – keshlam
    Oct 26, 2023 at 12:22
  • Is a grounding conductor run between the main panel and your subpanel? There should be only one ground for a structure.
    – Jon Custer
    Oct 26, 2023 at 13:33
  • Added info. All panels are connected by EGC. I am asking about gas/water because I do not know where those lines transition to non-grounding materials behind the walls.
    – Matthew
    Oct 26, 2023 at 14:44
  • @Matthew do you have any CSST (bendy gas pipe with the yellow or sometimes black jacket) in your gas system? Oct 27, 2023 at 0:28
  • 1
    @ThreePhaseEel none that I can see.
    – Matthew
    Oct 27, 2023 at 4:11

1 Answer 1

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Let's clear one thing up: your subpanel daisy-chain is already grounded. Let's label the panels for clarity

  • Main Panel A
  • Garage Subpanel B (connects to A)
  • Utility Room Subpanel C (connects to B)

By code, A has to have the ground and neutral bonded, and then the box must have a grounding rod as well. You said you have a Concrete Encased Electrode (CEE), which meets that requirement.

Subpanels in a different building have to have their own grounding rod hooked to the ground of the subpanel (not the neutral). Your subpanels are in the same building, so that doesn't apply.

Water lines are generally not required to be bonded to ground within your house unless they are metal. If you have metal pipes, there may be a need for a ground somewhere (i.e. you're hooking copper pipes to steel and want to reduce corrosion).

Gas lines might need a grounding connection. Depends a lot on your setup. Let's say your utility room is the ingress point to your house for the gas line. It would be code to hook your gas line to Panel C for the purposes of grounding the gas line, as Panel C is grounded already.

NEC does not permit bonding a panel to underground pipe for the purposes of grounding panels

NEC 250.52(B)(1)

(B) Not Permitted for Use as Grounding Electrodes. The following systems and materials shall not be used as grounding electrodes:

(1) Metal underground gas piping systems

(2) Aluminum

250.104 Bonding of Piping Systems and Exposed Structural Steel.

(B) Other Metal Piping. If installed in, or attached to, a building or structure, a metal piping system(s), including gas piping, that is likely to become energized shall be bonded to the service equipment enclosure; the grounded conductor at the service; the grounding electrode conductor, if of sufficient size; or to one or more grounding electrodes used. The bonding conductor(s) or jumper(s) shall be sized in accordance with 250.122, using the rating of the circuit that is likely to energize the piping system(s). The equipment grounding conductor for the circuit that is likely to energize the piping shall be permitted to serve as the bonding means. The points of attachment of the bonding jumper(s) shall be accessible.

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  • Are there downsides (other than cost) to bonding water and gas to ground at panel C, even if I am not required to do so?
    – Matthew
    Oct 26, 2023 at 19:03
  • Not really. The purpose of grounding there is to remove it from the pipe.
    – Machavity
    Oct 26, 2023 at 19:15

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