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Okay, I have a 200amp main panel with 2 hots and 1 bare wire connected to a bonded neutral and ground bar. I'm trying to run a sub panel off this and the new panel has 2 hots a neutral and a bare ground in panel. How do I connect the sub panel when I only have 3 wires? I do have the ground bar and neutral separated in sub panel. And should I use a separate grounding rod on sub panel?

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  • How did you come to have only 3 wires? Did you use metal conduit to connect the subpanel, and if so, which kind? Commented Feb 27, 2022 at 0:35
  • It was preexisting. I used 2/0 service cable
    – Sean
    Commented Feb 27, 2022 at 1:38
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    Are you saying that you used 3 wire cable for the run between the main and the sub, or that the cable coming into the main panel has only 3 wires in it? Commented Feb 27, 2022 at 2:00

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Your main has neutral and ground bonded, so Hot-Neutral/Ground-Hot

Your subpanel has isolated Neutral and Ground, so Hot-Neutral-Hot and Ground.

The ground connects to the SAME BAR as Neutral at the Main Panel, but NOT at the Sub-Panel.

Your grounding conductor can be metallic (non-flexible) conduit, if it's continuous and correctly assembled all the way from the Main to the Sub. So it does not HAVE to be a wire, but it still needs to remain isolated everywhere but at the Main from Neutral. If you bought cable with only 3 conductors, you made a mistake and will need different cable, or conduit and wires.

If the Main is correctly grounded and the Sub is in the same building, there is no need for a Grounding Rod at the Sub-panel.

If the Sub-panel is in a separate building, a Grounding Rod (or other acceptable Grounding conductor, such as an Ufer ground aka "concrete encased electrode") is required local to that building as well as the separate Grounding conductor (which can be metal conduit, or a green or bare wire) that goes all the way to the Main panel.

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