Fusing & Wire Sizing guidelines for solar panels 2022-04-10

Great info, diagrams and explanation.

However, even though a PV array of 2 strings doesn’t require OCPD per physics, per NEC it does. Refer to sec. 690.9(A)(1) item (2) of the 2020 NEC, and also https://explorist.life/how-to-fuse-a-solar-panel-array-and-why-you-may-not-need-to/.

Basically, if the sum of the short-circuit currents of each PV string in a PV array isn’t greater than the max OCPD rating of the panel (along with another condition), then no OCPD is required. Or equivalently, if the sum of the short-circuit currents of each PV string in a PV array is greater than the max OCPD rating of the panel, then an OCPD is required

Explanation of DC circuit breaker polarity and its proper use in 3 (or more) parallel strings of solar panel wiring found on page 12, Fuses vs. Breakers Directional or Polarized DC Breakers, is very precise. It was not immediately recognizable by me without the explanation.

High level data with code references.