I would like to retro fit a ground conductor from one sub-panel to another where both are fed from the main.

I purchased remote property in Alaska. It has a 200 amp Main panel and 2 subpanels. In the Main Panel the ground and neutral bar are bonded.

From the Main panel there is a 100amp breaker feeding 100amp subpanel A approx. 180 ft. away. The feeders to subpanel A are a 4 conductor cable 2-2-2-4 RUD alum. #4 being the ground. Ground and neutral are NOT bonded. Subpanel A feeds 2 R.V. parking spaces, shower house, bunk house, well and Some outlets. works great.

From the Main panel there is another 100 Amp breaker feeding 100amp subpanel B approx. 220 ft. away. The feeders to subpanel B are a 3 conductor cable 2-2-2 RUD alum. The ground and neutral bars are NOT bonded. There is No Equipment Ground conductor from the Main Panel to sub panel B. Sub panel B services a 2 bedroom 1000 sq.ft. very nice cabin fully furnished.

All 3 panels have ground rods attached.

I'm fairly sure after I need a #4 grounding conductor from panel B to get back to the bonded ground bar in the main panel for ground faults.

Can I retro fit a #4 conductor from the ground bar in Sub panel B to Sub panel A, as subpanel A has an equipment ground in place going back to the main panel, completing bonding and the distance is much less, 75 ft.

enter image description here

From comments provided in an "answer":

  • Yes Sub panel B Does have equipment grounding.
  • Yes I'm just missing the equipment ground feed from Sub panel B to the main panel.
  • No the feeds are direct burial, no metal conduit.
  • Was thinking I could tap off Subpanel A's equipment ground as its closer to Subpanel B.
  • Does your wiring in the cabin (subpanel B) have equipment ground conductor wiring, and you are just missing ground connection from subpanel B back to main panel? Is your feed from main panel to subpanel B inside metal conduit that might be used as the EGC between the two?
    – Armand
    Feb 24, 2023 at 2:19

1 Answer 1


That's fine.

However, #2 aluminum is not 100A wire. It's 90A wire. You'll need to downsize those breakers.

enter image description here

(People think it is 100A wire because an exception in code allows service wires to a dwelling to be sized 83% of service ampacity, so 83A to a 100A service. That doesn't help you any, your service is 200A).

Can you power two 50A RV stands from a 90A feeder? Yes, actually! Table 551.73. Based on the near nil chance both RVs will be maxed out at the same time.

  • 1
    And this is why the recommendation: USE CONDUIT!
    – FreeMan
    Feb 24, 2023 at 13:12

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