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This is the scenario:

  1. I have 400amp main service to my meter.
  2. I have a 400amp main panel that has 2x200amp circuits. The panel is grounded with bare copper wire 6ft apart with appropriate gauge wire (this was installed by an electrician and permitted).
  3. 1x200amp circuit is used as the main electrical supply for my house.
  4. I want to use the remaining 200amp circuit to supply a 200amp exterior panel that is about ~100ft away on a barn.

Questions:

  1. What type of wire should I use for this ~100ft run? Can it be 4/0 Aluminum?
  2. Can I use 3 appropriately gauged aluminum service wire to connect 2 of the aluminum wire to the 200amp circuit on the main house panel and the 3rd aluminum wire to the ground bus on the 400amp panel? Basically, can aluminum wire be used as ground wire to run from one ground bus to another?
  3. At the panel on the barn, do I need to "re-ground" the panel if the aluminum wire is connected to the main panel ground bus?
  4. I would plan for an 160amp draw (80% load of 200amp) at the entrance panel on the barn, is this the correct assumption?
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  • How much power do you actually plan to use in the barn? You mention 160A (80% of 200A) but is that what you really think you will use, or just "I know that is the most I could use based on a 200A breaker and feed wire"? If you only need, for example, 100A in the barn, then it may make a lot of $en$e to use smaller wire and replace the 200A breaker in the main panel with a 100A breaker. The barn panel can still have a 200A breaker as there it becomes just a shutoff/disconnect. Commented Aug 11, 2022 at 19:12
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    You need four wires: hot, hot, neutral and ground. This is unless all of your loads are 240 volt and even then, I'd run the neutral for the future.
    – DoxyLover
    Commented Aug 11, 2022 at 21:45
  • Can have 3 wires and steel conduit for grounding. Can't have less than 4 wires if non-metallic conduit (or, I suppose, overhead wire, but there it is still 4 wires. You didn't specify burial - are you going on poles or in conduit?) Anyway, you clearly don't understand how to run wire to a sub-panel, so you need to educate yourself seriously, or hire someone who knows what they are doing. It's not hard to do right, but it's easy to do wrong if you don't understand what you are doing. And right now, you evidently don't. That can kill you or other people, such as your family or friends.
    – Ecnerwal
    Commented Aug 11, 2022 at 23:24

1 Answer 1

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What type of wire should I use for this ~100ft run?

250 kcmil aluminum per NEC 310.15(B)(16).

There are no wins to be found in 310.15(B)(7) since that applies only to the whole service size (400A).

Can I use 3 appropriately gauged aluminum service wire to connect 2 of the aluminum wire to the 200amp circuit on the main house panel and the 3rd aluminum wire to the ground bus on the 400amp panel? Basically, can aluminum wire be used as ground wire to run from one ground bus to another?

If you want to power any 120V loads out of that panel, you are going to need a neutral. Neutral is not ground.

Neutral is generally the size of the hot conductors. Ground can be I believe #4Al.

At the panel on the barn, do I need to "re-ground" the panel if the aluminum wire is connected to the main panel ground bus?

Do you mean local ground rods? Yes, that too. You need all 3 things since they do 3 different jobs.

  • Neutral - return service current
  • Ground wire - return human generated fault current
  • Ground rod - return natural current, spikes, lightning, and prevent hazardous voltage gradients from making a difference between grounding system voltage and actual earth voltage.

I would plan for an 160amp draw (80% load of 200amp) at the entrance panel on the barn, is this the correct assumption?

Yes.

But no need to limit yourself to two F150 Lightnings :) you can have up to sixteen EVs as long as the wall charge units are using Share2 technology to coordinate with each other to not exceed 160A amongst them.

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