Hey ScottsAI-
that's a handy link you've got there. I usually go to my annotated copy of the NEC for such information. I'll try and remember to post the unit converter I use at work. . .
it is fascinating how fast I^2*R catches up to you when you're dealing with low voltages and powers, hey? the numbers commonly bandied about for mains service is based on fire prevention, not power conservation; and are based on the ability of the wire to shed heat and not melt insulation or heat nearby flamables. the code is a discussion of the minimum effort required to be safe-- there is nothing but budget and the aggravation of dealing with teminations to prevent us from using larger wire than called out in the code.
RE NEC: I never claimed to be to code. <G> claimed it was a way to do the job cheap, with minimal budget, tools, visual impact and skills, which seemed to be the overriding design criteria. Plus, we're talking laptop here. . . temporary wiring gets a looser code interpretation. . .<evil grin>
besides, the code is a little vague for low-voltage DC. even if it was nominally to code, I wouldn't count my chickens until I got the local building inspector to sign off. <G> and maybe not even then.
I didn't feel like grabbing a calculator, so I rounded up to make a 'back of my forehead' estimate based on my 120V experience. I took the inverter's nameplate output as a starting point. (I actually figured at 10A, and decided that less than 10% loss would be the cutoff. in retrospect, that was probably a little glib, as I forgot to account for the low-voltage cutoff feature most inverters have.) <G> given the total power budget and the cost and appearance advantages of 10-2 UF romex vs #8 or #6 THHN and conduit, chasing 1-2 W just isn't worth the time and effort. come to that, though, if the loads were better balanced, your multiple wires to the individual loads would work better from a loss point of view, as there would be more total wire area in 2 12awg runs than in 1 10awg conductor.
if we were trying to move 0.25 kW or more, believe me, i'd have answered much differently, and would, as you do, have favored the remote inverter option. for the viewing audience, the above discussion points up the desireablity of mounting your conversion equipment as close to the storage bank as possible.
RE soldering: you're right- the code specifically prohibits a solder-only joint; particularly in grounding conductors, you don't want to take the chance of the join heating up from excessive current, melting the solder and going intermittant! (i've seen it happen. . . . annoying to trace in a vibratory environment.
thus my call for a crimped and soldered connection; <G> crimp for mechanical strength and reliablity, solder for (slightly) lower losses and environmental reliabilty. and let's not get me started on wirenuts. . . .(ptui!)
-Dan