NEC Free AIR

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dean.thompsonIII

Member
Location
Sacramento CA
Occupation
Senior Electrical Engineer
If I have #10 AWG THHN wire bundled with a zip-tie every 6 ft and not in any raceway or conduit. Is this considered Free Air and is it still subject to bundling derate called in NEC Table 310.15(C)(1)? This is a PV application.
 
dean.thompsonIII said:
If I have #10 AWG THHN wire bundled with a zip-tie every 6 ft and not in any raceway or conduit. Is this considered Free Air and is it still subject to bundling derate called in NEC Table 310.15(C)(1)? This is a PV application.
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There is no specific definition of 'in free air'.
But if the conductors are touching each other, regardless how often the zip ties are placed, I would consider them bundled. If they are visible separated, by roughly 1 conductor diameter, I would say they are in free air.

Check with manufacturer or industry cable tray data for conductor spacing in free air.
 
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to discribe better this process we are using PV 10AWG which is rated for outdoor use. when bundling a total of 12 PV cables in open air the bundles are clamped approximately every 6 ft- 10 ft. Therefore, it seems that the heat produced by current is able to dissipate in what I see as FREE AIR but the NEC is not very clear with PV applications.
 
dean.thompsonIII said:
to discribe better this process we are using PV 10AWG which is rated for outdoor use. when bundling a total of 12 PV cables in open air the bundles are clamped approximately every 6 ft- 10 ft. Therefore, it seems that the heat produced by current is able to dissipate in what I see as FREE AIR but the NEC is not very clear with PV applications.
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You would use the normal table (NEC 2020 table 310.15(B)(16)). Arguments could be made for the wire being able to care more than that table but it will fall on deaf ears. Your install would require terminating those wires at terminals that are not exclusively rated for the free air ampacity. Terminals in free air are still only allowed the 110.16 (60°C / 75°C) ratings. As well as, if those conductors enter an enclosure prior to a splice or end up in conduit or another wiring method than you would need to use the lower ampacity per 310.14(2) anyway.
 
dean.thompsonIII said:
to discribe better this process we are using PV 10AWG which is rated for outdoor use. when bundling a total of 12 PV cables in open air the bundles are clamped approximately every 6 ft- 10 ft. Therefore, it seems that the heat produced by current is able to dissipate in what I see as FREE AIR but the NEC is not very clear with PV applications.
Click to expand...
12 PV Cables bundled like you describe are not single conductors in free air, see 310.15(C)(1) - The ampacity of single conductors not installed in a raceway but are installed without maintaining spacing for a continuous length longer than 24 inches shall be reduced per the table in that section.
 
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