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I'm installing a subpanel on the opposite side of my home. To be clear the subpanel will be attached to the same structure as the main panel (the main panel does have a grounding rod), just on the opposite side from the main panel.

Originally I was planning on installing a grounding rod for the subpanel, now since the main & subpanels will be on the same dwelling I'm not sure the grounding rod is needed.

Should I install new grounding rods for this new subpanel?

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  • Do not think you need an extra grounding rod by code, but usually the more the merrier. If you do add an extra rod think it has to be bonded(connected) to the other/s if in the same building.
    – crip659
    Apr 6, 2022 at 15:16
  • Couldn't that possibly cause issues with variance in ground potential, @crip659? I'm not certain, so I'm asking.
    – FreeMan
    Apr 6, 2022 at 15:17
  • Not sure myself, but do think they need to be bonded to each other. The sub panel needs a ground path(wire, metal conduit) back to the main, besides the rod. There are a couple of questions on the side of this that seem interesting.
    – crip659
    Apr 6, 2022 at 15:32

2 Answers 2

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No, you don't need separate grounding rods for a sub-panel in the same building. It just needs a 4 wire circuit (appropriately sized): 2 hots, a neutral and a ground. As always, the neutral and ground should NOT BE BONDED, so that means all neutrals go to a separate bus bar that's not connected to the Grounding bus bar, the grounding bar is where all the ground wires will go.

EDIT: Based on Ecnerwal's comment: be sure to remove the bonding screw(s), if present, to properly isolate the neutral from the ground. Some panels include the bonding screw loose, others have it installed. Again, bonding neutral to ground is a no-no. Thanks to Ecnerwal's helpful comment.

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    The neutral bar also must be isolated (insulated) from the case, as the case is grounded. In practice, you usually have to remove the bonding screw connecting the neutral bar provided to the case, and add the grounding bar (there are usually screw holes provided for adding one, two or more depending on panel/case size)
    – Ecnerwal
    Apr 7, 2022 at 13:44
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An Equipment Grounding Conductor (wire or qualified metal conduit system per NEC 250.118) is required with the feed from the main panel to the sub-panel. Supplemental or Auxiliary grounding electrodes at sub-panels in the same buuilding are not required but are specifically allowed by NEC 250.54.

250.54 Auxiliary Grounding Electrodes. One or more grounding electrodes shall be permitted to be connected to the equipment grounding conductors specified in 250.118 and shall not be required to comply with the electrode bonding requirements of 250.50 or 250.53(C) or the resistance requirements of 250.53(A)(2) Exception, but the earth shall not be used as an effective ground-fault current path as specified in 250.4(A)(5) and 250.4(B)(4).

Extra ground rods will reduce gradients and are almost never a bad idea.

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  • I think that last sentence is misleading. There's no reason to install extra ground rods in a residential building. It's a huge waste of money. For a sprawling commercial or industrial site, maybe, but not for a sub panel on the other side of the house. There are far more things that can go wrong when introducing auxiliary grounding. I'd say stay well clear of this, in general.
    – J...
    Apr 7, 2022 at 12:46
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    @J... Then write up answer, and back it up with some sources, rather than "drive-by commenting" FUD and your opinion for something that is explicitly blessed in code Also - grounding rods are not particularly expensive, so it's hardly a "huge waste of money" to add another one.
    – Ecnerwal
    Apr 7, 2022 at 13:24
  • @Ecnerwal An auxiliary grounding electrode is not a ground rod and must not be used for that purpose - I'm saying your answer is providing incomplete information and conflates what this code section is talking about. I don't have another answer to write because 250.54 is completely off-topic for this question - George's answer says it all. This is introducing new information and it's doing so in a way that is incomplete and misleading. The main danger of an auxiliary ground is circulating currents from lightning strikes. Adding one must be a carefully considered decision.
    – J...
    Apr 7, 2022 at 13:42

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