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I have a three-wire cable feeding a 60A sub panel from the main panel. Will a separate wire from the main panel to the sub-panel suffice for the ground or neutral in the sub? Separation of ground and neutral or bonding will take place in sub panel.

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    If the wires are in metal conduit, then the conduit is used for ground. I am assuming this is for a simple hot, hot, neutral North American system.
    – crip659
    Sep 28, 2022 at 13:03
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    If the sub is in a separate out building, it needs its own grounding rods.
    – FreeMan
    Sep 28, 2022 at 16:51

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I’m going to assume you don’t have separate wires in conduit since then you could just pull an additional wire.

The problem is that a neutral wire must be in the same cable as the hots. No exceptions. If your cable has a green wire or a bare wire, that must be ground and cannot be reassigned as neutral.

On the other hand, if you somehow has a red-black-white cable, you would be allowed to add a green or bare wire separately. It doesn’t even have to follow the same route as the main cable.

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  • Additional note: If there were separate wires in metal conduit, the conduit could be the ground. (as noted in comments on the OP, too.)
    – FreeMan
    Sep 29, 2022 at 14:53
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Also if you have a sub panel that is next to your main panel you do not want to bond the neutral and ground. This will cause a draw on any ground in your home because the neutrals and ground will be essentially on the same 'return' power. As stated before if the sub-panel is in another building it needs it's own grounding rod.

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  • It doesn't matter where the sub panel is, it should NOT have a neutral-ground bond.
    – FreeMan
    Sep 30, 2022 at 13:01

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