Thanks for the clarifications. Couple of niggling things:
-Mex, it's not always the panel output that counts. With 24v panel and 12v battery, the controller-battery path carries almost twice the amps the panel-controller path does, so ampacity requirement goes up.
-The wire gauge on the controller-battery path has to prevent voltage drop, have sufficient ampacity, and be fused to protect the wire "from the battery" but the current from the battery would be huge. I take it that if the wire is fused to the gauge for the controller output amps (and a bit more like 1.25 more) then that fuse will also blow if the battery shorts. That just leaves the piece of wire between battery and fuse to melt, which is why that piece is usually stated to be no more than 18 inches long (and not behind a wall I would think)
-The operating at 80% NEC guide/rule is for "continuous" (yes?) but the 1.25 over STC idea is for "occasional" times when the panel is doing more than its Voc /Isc at STC. So why can't the fuse etc be at just 1.25 too, not 1.56, since it is not expected to be running at 1.25 continually?
