[RE-wrenches] Battery Conductors and the NEC

[Chris Sparadeo]

Thanks for the thoughtful response, William. I do think article 100's
definition is ambiguous enough to make the case. I'm not sure that 310.16's
exceptions for derating a conductor (which would normally apply to
things like conduit fill, # of conductos, ambient temp) then allow that
conductor to be classified under table 310.17. Those conductors might not
have to be derated, but they are still bound to the limitations of 310.16.
Even if it's semantics, I think pleading "well ventilated" and starting in
310.17 is a better option. There isn't much conversation around this
subject and the hardened, old school electricians I interface with would
say that a nipple is still a raceway and absolutely not "free air". Point
taken about manufacturers, but then again they still often point to the NEC
for sizing requirements in their installation manuals.

On Thu, Mar 20, 2025 at 1:53 PM William Miller <william at millersolar.com>
wrote:

> Chris:
>
>
>
> 1:
>
> From Article 100 (2020 NEC):  Free Air (as applied to conductors). Open or
> ventilated environment that allows for heat dissipation and air flow around
> an installed conductor. (I did not find this definition in the 2017 Code.)
>
>
>
> 310.15(C)(1) Exception (b): Adjustment factors shall not apply to
> conductors in
>
> raceways having a length not exceeding 600 mm (24 in.) .
>
>
>
> The 310.15(C)(1) Exception (b) applies most specifically to more than
> three conductors in a conduit, but it makes a case that short sections of
> conduit are not treated the same as longer runs.  It might be argued that
> 24 in. or less of nipple or a cable tray is a “ventilated environment”.
>
>
>
> 2:
>
> Manufactured assemblies are not regulated by the NEC.  If the manufacturer
> recommends a specific wire gauge, and particularly if they provide that
> wire, then the case can be made that it is approved.
>
>
>
> I hope these interpretations help.
>
>
>
> William
>
>
>
> Miller Solar
>
> 17395 Oak Road, Atascadero, CA 93422
>
> 805-438-5600
>
> www.millersolar.com
>
> CA Lic. 773985
>
>
>
>
>
> *From:* RE-wrenches [mailto:re-wrenches-bounces at lists.re-wrenches.org] *On
> Behalf Of *Chris Sparadeo via RE-wrenches
> *Sent:* Thursday, March 20, 2025 10:09 AM
> *To:* RE-wrenches
> *Cc:* Chris Sparadeo
> *Subject:* [RE-wrenches] Battery Conductors and the NEC
>
>
>
> Hey everyone,
>
> I’m looking for some clarification on conductor ampacity ratings as they
> relate to battery cables. My understanding is that the term ‘free air’
> wasn’t actually defined in the NEC until 2020 and that conductors installed
> in a nipple, wire trough, conduit body, or enclosure don’t qualify as ‘free
> air.’ That said, I’ve noticed some battery manufacturers and installers
> seem to be applying Table 310.17 (free air) rather than 310.16 (raceway)
> when specifying conductor sizes—particularly for battery-to-inverter
> connections.
>
> For example, a battery manufacturer offers a 48Vdc LFP battery with 10kW
> continuous output, which would suggest needing a conductor rated for ~245A
> (safety factor included). However, they provide a wire trough for the
> battery to inverter connection and provide a 1/0 Cu battery cable. This
> seems undersized if 310.16 applies. Am I overthinking this, or are these
> configurations typically tested and listed accordingly?
>
> I see similar situations across multiple manufacturers, and while I don’t
> put too much trust in marketing images, I noticed SimpliPHI using a single
> 1-1/4” conduit from a stack of 6.6 batteries to a 15kW inverter, which also
> raises questions. Is there a code-compliant rationale I’m missing, or are
> manufacturers and installers misapplying Table 310.17? I spoke with one
> applications engineer that referenced table 310.17 as the “battery cable
> table”. I get the value of running free aired battery cables with regard to
> ampacity allowance, but I also see the value in protecting energized
> conductors in a raceway. Would love to hear your insights!
>
> Best,
>
> Chris Sparadeo
>
>
>
>
>
> C_802-369-4458
>
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