If I were to replace the wires from my battery to the distribution box in my trailer I would use 12ga stranded wire with a 20 amp fuse in an inline holder located about a foot from the positive terminal. Here is why. First I have a single group 24 battery. If everything in my trailer were on at the same time, let's say I have 4 lights
that were still incandescent (6A), a fantastic fan on high speed(3A), a furnace
fan (4A), and a water pump (2A), I have a total load of 15 A. If one wants to add a danfoss fridge
or charge their computer there is still capacity to do so with a 20A. service. Next, the resistance of 10 ft. of 12 ga. wire calculates to 0.016 ohms. At 20A. a voltage drop of about 1/3 volt would occur. If I were to use 14 ga. wire the resistance would be 0.025 ohms and a voltage drop of about 1/2 volt would occur. I agree with Byron, both are insignificant. I would choose 12 ga. wire over 14 ga. wire for mechanical reasons. It will handle the vibrations and wear and tear longer. Can I use 10ga? Sure. But it would be like using a grade 8 bolt where a grade 5 would work.
Now if one wishes to run their microwave
, big screen TV, food processor, air conditioner etc. while off grid they will need an inverter to produce a 120Vac 60hz. voltage. The only way to equate AC to DC is through power, i.e. Pac = Pdc. Since power = voltage x current, a lower DC voltage means high DC current and thus a larger gauge wire, more and larger batteries,etc. And with such high currents I would be inclined to continually check all my connections for fear of one loosening and overheating. It just isn't worth the hassle to me but as Donna likes to say YMMV. Raz