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I'm planning to run a #2 Aluminum conductor ("XLP/USE-2 or RHH/RHW-2") from my new 200A panel to the water pipe as a bonding conductor (80 ft distance). If I run the bonding wire in a PVC conduit back to the panel, can I use the bonding wire also as a ground for a 50A circuit that I'm planning to run in the same conduit? In other words, can I run 2 hots and a neutral (#4 Aluminum for my 50A 240V stove circuit, and use the #2 Al bonding conductor as my ground? What if I also add a 30A 240V circuit for a future heat pump water heater (#10 THHN Copper) in the same conduit, can I use the bonding conductor as a ground for that circuit as well?

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    Is all this stuff in the same conduit? Then 250.122(C) can apply. Otherwise you're going to need a ground per circuit.
    – KMJ
    Aug 15, 2023 at 22:59
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    You know you can use the 75C thermal table with individual wires, right? Though yes you'd need #4 to a 50A range if it was sharing the pipe with other live circuits. Anyway, a 30-60A circuit only needs a #10 Cu or #8 Al ground. The code you'd be looking at would be 250.130. Aug 16, 2023 at 18:05
  • @Harper-ReinstateMonica is there any derating for the ground in a conduit with 4 current carrying conductors? Or is #10 Cu fine for the ground for the 50A and 30A circuits? Aug 16, 2023 at 20:43
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    It's the same code reference I used when installing two 30A circuits recently in my house. The big thing to keep in mind is that you need to connect everything so that if you disconnect one of the devices (receptacle or appliance) the other one stays grounded at all times. No running all the grounds in to a wire nut, it has to be something like a bus, independent ground ears, or a Wago.
    – KMJ
    Aug 16, 2023 at 21:25
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    @ChristianK In a split-phase 120/240V circuits, all circuits have exactly two current carrying conductors for the purpose of the derate. If a second circuit is present, #8 caps off at 44A. See 250.122(B) for the "enlarge grounds if conductors are enlarged" rule. Since #6 Cu has the minimum ampacity for the intended installation (with a second circuit), I believe #10 ground should suffice. Aug 17, 2023 at 4:43

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Recently discussed here.

Upgrade Nongrounding Receptacle near Aluminum GEC?

Unless you are bonding within 5 feet of the water service entrance, the bonding wire is not considered GEC and can't be used as an EGC. If the 80 ft run does get all the way to entrance, then you can use it possibly for retrofits, but that is limited to replacing non-grounding receptacles and extending existing circuits. This does not apply to a new panel.

If you run a new 50A circuit then you have to run at least one new ground wire in the PVC raceway. Reference NEC 250.122(C). For a new circuit, the water bond doesn't count as a ground wire.

2014 NEC added an exception in 250.121(A) if you can meet the requirements regarding objectionable current. But really, how easy is it to add a 10 ga grounding wire in the same conduit for your new circuits?

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  • I am bonding within 5 feet of the water service entrance, but you are right that adding one #10 Cu wire isn't that big of a deal. Aug 16, 2023 at 20:46

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