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Can I make a 10 foot long single 4 gauge grounding wire from several twisted 12 gauge solid copper wires?

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    .... for "several" = 7.
    – Dave Tweed
    Commented Aug 28, 2017 at 18:48
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    But an electrical inspector may not approve. Commented Aug 28, 2017 at 19:44
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    Is it worth the hassle when you can get 10' of 4 awg thhn for <$10? Commented Aug 29, 2017 at 11:08

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#4 has a area of 41,742 CM (Circular Mils).

#12 has a area of 6,529 CM.

As Dave Tweed says in the comments, you need 7 (6.39) connected in parallel.

Parallel conductors are permitted by electrical codes for phase, neutral or ground for #1/0 and larger. Each conductor must be same length, material, insulation, area and termination. The parallel conductor rule is set up for currents > 250A.

As Peter Bennett says, an electrical inspector will probably take exception to this because #4 is readily available.

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    I think he's talking about field fabricating a single stranded conductor here, not multiple parallel conductors, and I have NFC how an inspector would deal with that considering that bare copper wire typically doesn't receive a listing in and of itself... Commented Aug 29, 2017 at 1:55
  • Conveniently, 7 is also the proper bundle size for a minimal stranded cable (one in the middle and 6 around it.) The next step is 19 (7 like that, 12 more around them.) So if you do a half decent job, there are going to be few clues indeed - and little reason to look for any clues in the first place. Just do a "workmanlike job" and you should be free and clear.
    – Ecnerwal
    Commented Aug 29, 2017 at 2:30
  • @ThreePhaseEel Aside from the question, I make no assumptions. We have no idea of the location, application, duration or certification. Commented Aug 29, 2017 at 18:23
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Can I make a 10 foot long single 4 gauge grounding wire from several twisted 12 gauge solid copper wires?

Yes

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