I have a question for regarding the definition of "Free Air". I have attached a photo of an older installation. You will three (3) large disconnects. Inside each disconnect is an old Klockner Moeller 800AF/AT Breaker. On the line side of each breaker lands two (2) sets of 3-1/C 500MCM (insulation type unknown). The other end(s) terminate onto the ATS you see on the far left. I highly suspect the termination provisions on the KM breakers are not 90C rated; therefore, I would have to utilize the 75C column, yes? The problem is...
Do I use the "Raceway, Cable, or Earth" or "Free-Air"? I suspect "R, C, or E" as there is a fair amount of the cable protected/supported by conduit/weatherhead and enclosure.
Based on what I see (as explained above) it would appear the designer/installer based the wire size on either:
a) 90C column of "Raceway, Cable, or Earth" which would handle 860A, or
b) 75C column of "Free Air" which would handle 1240A (overkill)
Assuming the termination provisions are 75C and the cable can not be classified as being "Free Air", it would be safe to say this installation is not to code given that the cable would only be able to to support 760A (before temp correction factors, derating, etc) and the breaker is 800A.
I welcome any comments on my thinking/logic.
Thanks in advance for you time!