Here's my take on voltage drop with wire gauges: The cost of wire between 12 AWG and 4 AWG is is about $.50/ft.-> $.75/ft., depending on where you source wire. I paid some fairly good money for my solar system and spent a lot of time on it, both in front of a screen, researching, and in the shop fabricating pieces of it.
My trailer is 22' long so the greatest amount of wire run could be 50' (both phases) to connect modules with controller. I asked myself, " will I try to cut costs and live with any voltage drop for the maximum of $25 saved?", when selecting wire sizes. Answer to self was, "NO, I don't want to lose a single watt of power harvested, if possible". Granted, all wire has resistance and there will inevitably loss of power but I chose not to go with the accepted 3% or 5% of loss due to the cost of wire.
As the wiring schemes of my install developed and I started searching for sources of wire, I ended up with a 150' reel of 4 ga. and that's what I used throughout. I'm not advocating that you use the same, my point is that there is little sense to use wire that impacts the efficiency of your system beyond 1%.
Southwire voltage drop calculatorWaytek wire is where I sourced wire and connectors. They are local to me and establishing a contractor level account is necessary.
Genuine dealz is a distributor used by many on the Forum, they will make custom cable/connectors and offer a variety of different wire products.
Good luck with your wiring!
