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We purchased three-conductor 2awg cable. It has 2 insulated wires surrounded by a neutral/ground. This cost $150, and since it was bought by the foot, I don't believe we can return it.

Can we still use this to run the subpanel, using the the 3 wires as L1 and L2 and neutral, and running the ground to existing grounding rods outside that building from the panel?

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  • What loads are you putting on this subpanel?
    – ThreePhaseEel
    Nov 13, 2017 at 2:44
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    Earth ground is NOT the same as a safety (grounding) ground. The safety grounding conductor that runs back to your main panel, is a low resistance path back to the source that allows faults to be cleared. The metal rods in the ground are for equipotential bonding, and lightning protection. You cannot replace a safety ground, by sticking metal in the dirt.
    – Tester101
    Nov 13, 2017 at 4:07
  • 100amp subpanel
    – Samantha
    Nov 13, 2017 at 8:47
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    You can return it if he lied to you / misled you. Worst case you charge back the credit card. Lowe's doesn't like it, but they also know this is the price they pay for paying $9/hr for their clerks and overcharging on most items to the point where no electrician would ever shop there. (Not the items you'd check, of course). Now stop in at a real electrical supply house, or browse a few, they're not "retail friendly" but they're good.
    – Harper - Reinstate Monica
    Nov 13, 2017 at 17:43
  • Curious which specific cable you got. I only see one 2/2/2 with outer wrap ground in Lowes' online catalog: + it's aluminum, + for direct burial, - no good for anywhere near 100A. Just for reference, aluminum is actually better for large wires than copper. Far cheaper, and less corrosion problems because the lugs are aluminum.
    – Harper - Reinstate Monica
    Nov 13, 2017 at 18:03

2 Answers 2

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Just get the correct stuff and run it -- anything else you do's going to be a way bigger pain in the arse

Since you (presumably) have not put the wrong cable in the ground yet, your best bet is to simply get the correct cable (one with 3 insulated wires and bare ground) and run it. If you can't return the incorrectly purchased cable, just toss it in with the next load going to the metal scrapper in your area -- you'll at least get a little bit of money back for it that way.

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  • Unfortunately I'm not at a place where throwing $150 in the garbage is something I'm really wanting to do. We wanted to run 100amp subpanel.
    – Samantha
    Nov 13, 2017 at 8:45
  • Could they just add an one more insulated wire as the neutral and run all of those in conduit?
    – kponz
    Nov 13, 2017 at 15:23
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    @kponz interesting idea, the conduit might make that legal. OP also did not say whether they have Al or Cu or how far they want to go. I hope they didn't get Cu, waste of money and corrosion hazard. Also they didn't say what cable type and it may not be outdoor rated.
    – Harper - Reinstate Monica
    Nov 13, 2017 at 17:37
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OP is possibly using what I believe to be SEU cable ( based off of OP's description of the cable ). SEU CANNOT be run in conduit.

In order to add a sub panel you'll need to run 2 hots and a common, of the appropriate gauge which #2 is to my knowledge, along with a ground from your existing panel to your sub panel.

It's unclear to me where this new sub panel is located. If it's in the same structure or a different structure as the main panel.

Code requires 2 grounds. They can be dual grounding rods, with an unbroken #4 ground wire running between them and the main panel, or a cold water ground and ground rod, as long as the cold water ground is located within 5 feet of where the cold water enters the dwelling. That's assuming your incoming cold water line is metallic ( copper, galvanized ). If your sub panel is located in a different structure, additional ground rod(s) will need to be added there as well...

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    Are you sure it's SEU and not single-rated USE(URD)?
    – ThreePhaseEel
    Nov 17, 2018 at 21:20
  • Actually, no... I'll adjust my answer accordingly.
    – BillWeckel
    Nov 17, 2018 at 21:26

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