As I understand it, you have an array that outputs 7.5A. You fuse it with 10A. A 10A fuse does not open at 10A. It may take 10 minutes to open at 135%, or at 13.5A. Your array has a short current current about 10% greater than Imp. That means in your case short circuit current is 8.25A.
So you see, a short will generate 8.25A. The fuse won't blow till 13.5A. It serves no purpose. It will never blow.
Cal
So here's the scoop....
I will explain the reasons for the need to fuse the wire between PV's and Charge Controller. There are 2.
Attached is a picture of my home-grown combiner box which used to accommodate 4 breakers for 4 PV's in parallel, and conveniently made into an illustration (I hope).
*Illustration Notes:
RED Wires/Arrows/Labels: Pos. Current Flowing Under Normal Conditions
RED & Black Arrows/Labels: Pos. Current Flowing Under Shorted Conditions
Reason 1: 3 or More PV's in Parallel - One PV shorts
If one of the PV's (PV #1 in our case) shorts, the 2 other PV's will supply a 10A current (back-feed) through the PV #1 wires. These wires may now be undersized and it and the PV will fry.
Reason 2: Charge Controller Shorts
If the charge controller fails and shorts, the 20A current from the battery will flow towards the PV's. The wires after the combiner and Pv's are rated for 5A, so again things can fry.
*From the Manufacturers: A PWM controller has the ability to have current flow in reverse under failure/short in some scenarios. An MPPT controller apparently cannot (but this is not definitive).
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REBUTTALS:
I erred in me previous postings... I have 5A breakers (not 10A) protecting each PV that is Isc: 5.85A or Ipm: 5.45A, but under normal operating, the max. range is 4.33A -ish.
BUT, as you can see, I now run 2 PV's (each with 3 panel's wired in series @ 36v), SO I no longer have or need protection for Reason #1, but since the fuse is under the PV's Isc: 5.85A, it does add another layer of protection (Reason 3?)
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