1

I've installed a new subpanel and service cable, upgrading it from the 30 amp to 100 amp. I installed a new grounding rod and wire to the new panel. I noticed on the old panel and the main panel, the ground wire is routed away from the power service cable. It seems to run separately and comes through an independent hole in the panel.

Does the ground rod wire need to be separated this way, or can it route into the building through the same hole and come up into the panel through the same panel hole as the power cable?

Additional info per @Greg Hill: The service runs underground from the main house in PVC conduit, using AL 2-2-4-6 mobile home feeder cable. It is protected through the full run and not exposed at any point outside the main house and small guest house we are renovating. The grounding rod is embedded in the earth about 2' from the wall where the subpanel is mounted inside. The copper wire runs up the wall and enters the guest house at the same point the service cable enters, then follows the service cable run up into the panel (approx. 5'). There is another grounding wire that is embedded on the opposite side of the building where the previous subpanel was mounted. I am not attached to this wire for the new panel. The mobile home feeder cable ground is attached to the ground bar in the main house, and to the ground bar in the guest house subpanel. The guest house subpanel is not bonded.

2
  • Either way can be done but there are conditions attached. This is an underground service? Is the service cable mostly direct buried, entering conduit only for protection to rise up from the soil to the panel? Is the conduit ferrous (EMT, rigid, etc) or non-ferrous (PVC, aluminum, etc)? Is this service to a site-built home? Is there another grounding electrode present (copper water line, rebar in concrete, etc)? Click the 'Edit' text below the question to revise and add more details.
    – Greg Hill
    Commented Aug 23, 2021 at 18:59
  • You may have a hard time arguing with an electrical inspector that the feeder of your guest house feeds the entire load associated with a unit of a multifamily dwelling unit where NEC 310.12(B) allows #2 al to be protected at 100A rather than the normal 310.16 limit of 90A. Commented Aug 24, 2021 at 2:27

2 Answers 2

1

The ground wire you refer to is also known as the grounding electrode conductor. You should already have a grounding conductor coming from the feeding panel to this new sub panel you've put in. Generally speaking, you would bring the grounding electrode conductor through its own hole rather than through the entry with the other cable, just to make sure that you're protecting your main cable. The main cable feeding that sub panel should have either its own clamp fitting or conduit fitting where it attaches to the sub panel. The grounding electrode conductor is not usually clamped, just brought through one of the tiny knock-out holes designed for it in the bottom of the enclosure.

1

It's ok for that grounding electrode conductor to enter the building through a wall penetration shared with the service cable/conduit.

IMHO the conductor should have a clamp to provide strain relief where it enters the subpanel just as would be done for any cable (ie conductors/cable not inside conduit).

You've done well in providing a ground conductor from the main house to the guest house, and in also providing a ground rod at the guest house -- but when the grounding system includes a ground rod, a second ground electrode is required (or specific testing to demonstrate that the one rod is good enough). In other words you'll actually need two ground rods and they should be separated by at least 6 feet.

Grounding electrode conductors must be continuous (or may be spliced with permanent means such as cad welding) -- this means it's complicated to extend the wire from the existing rod on the far side of the house, and also complicated to extend the wire from the new rod.. so probably your easiest and cheapest option is to drive a second rod and run a new conductor to it from the new sub panel. It'll be parallel with the other ground electrode conductor for part of the run, and that's okay.

1
  • Thanks Greg. One of the challenges I have with another grounding rod is I can't believe how lucky I was to get this one in the ground. I live in the mountains and solid bedrock is only a few feet down. I must have found the only place on the property where the rod actually went in all the way. I know where the other rod is. I'll see if I can run a new conductor from that one. Thanks for the advice!
    – Jon
    Commented Aug 24, 2021 at 12:25

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.