[RE-wrenches] Battery Conductors and the NEC

[William Miller]

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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