It is not mandatory to have fuses for your system to function properly.
Inline fuse for solar panel.
This means each series needs a fuse breaker placed in the combiner box as shown here.
Fusing solar panel arrays wired in parallel.
Between the charge controller and battery bank solar connector inline fuse between the charge controller and solar panels anl fuse set fuse.
Commercially made solar panels over 50 watts have 10 gauge wires capable of handling up to 30 amps of current flow.
The size of this fuse is dependent on how many solar panels you have and how they are connected series parallel or series parallel.
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Now in the case of 3 panels in series and 4 strings in parallel if one string shorts the max amperage to short is 39 12 which exceeds the 30 amp max current rating of the 10 awg wire.
However we do recommend to add fuses to prevent any mishaps.
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We recommend adding two different fuses in the following scenarios.
If you connect these panels in series there will be no increase in current flow so fusing is not required for this string.