awesome, but a bit over this dinesour inspector's head... as is most Solar.
For conversations sake...and to teach me a bit... let's assume the combined Isc from my combiner box to my inverter is 60 amps. NEC states my conductor ampacity must be 1.56% or 94 amps. Assuming THWN-2 conductors I can use a #4. Derating my #4 for standard reasons (fill, ambient) and assuming 75° terminations I should be fine supplying a 60 amp overcurrent device ? (or would that OCP need to be 125 of my combined module Isc ?)
Taking your example:
Given that standard test conditions total Isc is 60 A.
Max continuous current = 1.25*Isc = 75A
Sizing calculation for OCPD's = 1.56*Isc = 94A
This means we'd need 100A worth of overcurrent device if required. And we'd need 94A of termination ampacity.
Most terminations are rated 75C. For 100A and less, you need to check. Assuming such, this would mean a #3 Cu conductor is required for terminations, given that 1.25*1.25*Isc = 94A.
Now the conditions of use. A temperature correction factor of 0.82 is very common. We're talking 33C ambient and a durablock's height above the roof. Another common one when not in direct sunlight is 0.96, which I call the "basic derate" for simple ambient temperatures, and if this is all that there is, it usually will not affect conductor selection.
Standard 30C ampacity of #3 Cu THWN-2 in the 90C column = 110A
Adjust for 0.82 temperature correction: 0.82*110A = 90.2A
Now you might think that this calculation has to at least be 94A, and so did I at one point. But it doesn't. You do not apply both 1.25 factors when doing derates, only the first enhancement factor. Once you apply the enhancement factor, you treat it as any other continuous load.
You only need 1.25*Isc worth of conductor ampacity to satisfy the second condition. In this case, we need 75A worth of conductor ampacity, and we have 90.2A. So far, the #3 wire is still good.
Finally, the OCPD,
where required, shall protect the wire as sized. This means that both the termination ampacity and the derated conductor ampacity must round up to the actual OCPD (for 800A and less), or be greater than the actual OCPD for over 800A. An obscure rule, thanks to 240.4(B), but it certainly is strategic to make use of it. Where OCPD is not required, and not part of the design, you don't need to think about this. Where not required, but somehow there anyway, you also don't need to apply this rule. I suppose in concept you could have 100A worth of wire landing on an unnecessary 200A breaker where OCPD is not required, but it would raise questions when reviewed by anyone else.
So. We've determined a 100A OCPD, with #3 wire. Does the 100A OCPD protect it?
Its termination ampacity is 100A. Good
Its derated conductor ampacity is 90.2A. OOOOOO!!!! this is interesting. We've exceeded the previous OCPD by just a fraction of an ampere. But it still rounds up to 100A. Therefore, the 100A OCPD still protects the #3 wire, and thus the #3 wire is sufficient for local factors only.
Next comes voltage drop, which is a story for another day. And not as firm of an NEC requirement as the local factors.