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Thread: Romex for DC run

  1. #11
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    Assuming you are speaking about source circuit conductors, there would be numerous encumbrances to use of NM "romex:"


    First, the location is almost certainly going to be damp or wet. Not allowed to use NM in this location. 334.12(B).

    Second, there will likely be be numerous questions about exposure to physical damage, mitigation of which could make NM cable not worth the cost.

    Third, you would likely have to transition to another wiring method via a junction box or something, to connect to the modules (can't just strip the romex and leave it in the air.

    PV Wire (which usually us a USE-2/RHW wire with a 2000V rating and marked as PV wire) is readily available nowadays.

    Regarding the comments on the need to guard conductors or enclose in a raceway per 690.31, this requirement could apply, regardless of if one is using NM cable, or PV Wire. This would be a conversation to have with the inspector in many cases, as to is the wires are considered readily accessible. here are some examples of interpretations of 690.31:

    - An unfenced ground mounted solar array in someone's yard would have conductors that are readily accessible, and would need either guarding or raceway.

    - A PV install on a rooftop would require the use of ladders, and would therefore not be readily accessible.

    - A commercial PV installation with a fence meeting the requirement of 110.31 would meet the requirement for being "guarded" and the conductors inside would not have to be enclosed in a raceway simply due to their being readily accessible.

  2. #12
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    So I read all the posts and if I read them correctly, the only approved flexible cable assembly for DC PV run is type MC?

  3. #13
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    Read 690.31(G). That's basically correct but there's still a bit more to it.

  4. #14
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    Quote Originally Posted by five.five-six View Post
    So I read all the posts and if I read them correctly, the only approved flexible cable assembly for DC PV run is type MC?

    Inside a building, if it is not otherwise inside a raceway, yes. DC circuits from solar arrays, have to be in metal, in some form or another. This would either mean using metal clad or armored cable, or using a metal raceway.

    Outside within the array field on the racking, you do have other options for using a multiconductor cable, if it is either "guarded" by being not readily accessible or by being behind a locked fence. The cable you would use would have to be listed for use in a wet location, UV stable, and if your system is over 600V, it would also have to carry a special voltage rating. NM cable (e.g. Romex) meets none of these requirements.
    Last edited by Carultch; 04-19-19 at 07:20 PM.

  5. #15
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    Quote Originally Posted by Carultch View Post
    Inside a building, if it is not otherwise inside a raceway, yes. DC circuits from solar arrays, have to be in metal, in some form or another. This would either mean using metal clad or armored cable, or using a metal raceway.

    Outside within the array field on the racking, you do have other options for using a multiconductor cable, if it is either "guarded" by being not readily accessible or by being behind a locked fence. The cable you would use would have to be listed for use in a wet location, UV stable, and if your system is over 600V, it would also have to carry a special voltage rating. NM cable (e.g. Romex) meets none of these requirements.

    Good info, this first job I’m doing is on my own home and getting a raceway from the array would be an absolute nightmare with windows doors and eaves in the way there is no elegant way to make a run however with a new roof penetration, I can easily intersect the path that my #4 is taking from the new panel to the water service.

  6. #16
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    Quote Originally Posted by LarryFine View Post
    690.31 Methods Permitted.

    (A) Wiring Systems. All raceway and cable wiring methods included in this Code, other wiring systems and fittings specifically listed for use on PV arrays, and wiring as part of a listed system shall be permitted. Where wiring devices with integral enclosures are used, sufficient length of cable shall be provided to facilitate replacement.
    In the '17 Code there is an important 2nd paragraph.
    At my age, I'm accustomed to restaurants asking me to pay in advance, but now my bank has started sending me their calendar one month at a time.

  7. #17
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    Yeah, really bad idea

    Ignoring the fact that the NEC says this isn’t allowed (unless the voltage is less than 30VDC ...), it’s just a bad idea. A large part of the problem is that you’re either on the “battery” side of a system with batteries, or you’re on the photovoltaic side. If you’re on the “battery” side, you won’t have enough current at less than 30 volts to be useful. If you’re on the PV side you have to derate by something like 156%, which makes matters even worse.

    Anyway, DO NOT DO THIS. It’s just plain pointless.

    Obviously, once you’re on the AC output side, Romex is fine so long as Code permits.
    Julie in Austin

    Born to brew, forced to work ...

  8. #18
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    Quote Originally Posted by five.five-six View Post
    So I read all the posts and if I read them correctly, the only approved flexible cable assembly for DC PV run is type MC?
    yes MC for cable assembly.

    flex conduit is also an option but it of course has no wires

  9. #19
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    Quote Originally Posted by five.five-six View Post
    Good info, this first job I’m doing is on my own home and getting a raceway from the array would be an absolute nightmare with windows doors and eaves in the way there is no elegant way to make a run however with a new roof penetration, I can easily intersect the path that my #4 is taking from the new panel to the water service.
    For anyone wanting to run Romex or where conduit is difficult or ugly: I recommend a micro-inverter system.
    No DC. All AC. You can run all the Romex you want.

    E.g. new construction: rough-in romex in walls if home-owner wants no conduit visible.

  10. #20
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    Quote Originally Posted by five.five-six View Post
    Good info, this first job I’m doing is on my own home and getting a raceway from the array would be an absolute nightmare with windows doors and eaves in the way there is no elegant way to make a run however with a new roof penetration, I can easily intersect the path that my #4 is taking from the new panel to the water service.
    Depending on specific eaves windows etc......Consider running down other side of house and across crawlspace....., sometimes an option....., sometimes too much work.

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