xara
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- minneapolis, mn
why did they add the term "free air" to chapter 3?
free air
- Thread starter xara
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petersonra
Senior Member
- Location
- Northern illinois
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- engineer
Its been there a long time.
Conductors that are not enclosed dissipate heat faster than conductors that are in a raceway or a wall or enclosed in some other fashion, so their ampacity is increased.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Assuming you mean in the tables for ampacity, like Table 31O.15(B)(17) (formerly Table 310.17), some time between 1897 and 1975 when I started, because it was there the first time I read the NEC, but it's not there in the first edition.
Which is an interesting read by the way, all of 56 pages of it! (including the index and table of contents...)
https://archive.org/stream/00701897/0070-1897#page/n55/mode/2up
Julius Right
Senior Member
- Occupation
- Electrical Engineer Power Station Physical Design Retired
In my opinion, these tables- Table 310.15(B)(17) and Table 310.15(B)(19)- may be use for single-core cable [up to 2000 V rated] laying on a cable tray in a single layer with a maintained space of not less than one cable diameter between individual conductors [not in a solid bottom cable tray].
See NEC 392.80(A)(c)
See NEC 392.80(A)(c)
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