How to properly fuse a solar PV system - WindyNation How to properly fuse a solar PV system. If your panels are smaller than 50 watts, and use only 12 gauge wires, and 20 amp fuses are required. Parallel/Combiner Box fusing. In a parallel system a combiner box is used that holds the fuses/breakers to each panel, plus one or more “combined” fuse leading to the charge controller or grid tie How to Fuse your Solar System - Renogy United States For instance, if you have one of our 40Amp charge controllers, we would recommend using an 40Amp fuse second fuse between your solar panels and charge controller is a little bit different to figure out. The size of this fuse is dependent on how many solar panels you have and how they are connected (series, parallel, or series/parallel).