ECN Forum Forums Code Related Discussion NEC & other Code issues Free Air

Referencing Table 310.19 it states the following:

Table 310.19 Allowable Ampacities of Single-Insulated Conductors, Rated 0 Through 2000 Volts, 150 degrees Through 250 degrees (302 degrees F Through 482 degrees F), in Free Air, Based on Ambient Air Temperature of 40 degrees C (140 degrees F)

Does anyone know of a reference that specifically states the definition of "Free Air"?

I appreciate anyones help.
Brian

Boxford:
I'll take a stab at "free air"...
The best street definition I can come up with is an installation as the utility companies use. Single conductors mounted on cross arms or similar approved methods on poles. I could take it a step further and mention the "older" rack service drops at some commercial buildings; a "rack" is mounted to the exterior wall, on which insulators are mounted, and individual conductors are mounted to the insulators. This is not a commonly used installation now.
Hope this helps
John

Single conductors, spaced more than one diameter apart in a ventilated (ladder type) cable tray, are usually considered to be "free air".

Ed

and i thought i could fill my tires for free here, so much for livin' in the past eh?

I really appreciate everyones help.

Brian