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Thanks for the information InPhase, after looking at this for some time it seems like the guidelines are under par and using them and your best guess is the way to go. I am putting 300 amp breakers or fuses in the system to keep the amps where they can be controlled so I think with my setup my 0/2 should be more than enough, especially after hearing that the inverter will never even do enough to get close to pushing the amps up.
The challenge becomes trying to use any chart including the NEC one for something like power delivery in a DC system at short distances since the chart doesn't include cable with higher temp ratings like 105C, 125C and 200C rated cable(or at least I can't find an NEC chart with the higher temp rated cable in my code book). How you install or use the cable also makes a big difference on its allowed ampacity. Its always a good idea to go over board on the cable in stationary battery systems to limit voltage drop. I know from personal experience winding my own transformers that I can get around 200 amps through 12AWG wire for about 5-10 seconds before it begins acting more as a slow blow fuse.
The 2/0 cable you are using should be more than sufficient.
i use class t fuses in a class T fuse holder. i use 4/0 wire and a 400 amp class t fuse between the inverter and the 24 volt LiFePo4 battery on the 8000 watt lf sp psw powerjack inverter. i have not put it to the limit test so no where near 4000 watts at this time.
i like the class T fuses and have had zero problems with them.
i also have 300 amp class t fuses on a 6000 watt powerjack lf psw sp inverter hooked up to a different lifepo4 24-volt battery. possibly a smaller 1/0 cable there and still nowhere near the possible 3000 watt potential output.
the wire size between the inverter and the battery should be sixed as large as you expect to pull and the fuse should be 1.25 times larger than the largest amp draw you expect to use. that a rough rule of thumb for fuse sizing.
i crimp the lugs hydraulically ti match the bolts in the class t fuse holder. I think as many other do >>> it is best to use as heavy gauge pure copper wire as you can dso it does not overheat and become the fuse.
you can buy lugs with walmost any sixe hole to match you cable and bolt down needs.
bolt down class T fuses are the overcurrent protection i like the best. 😎
there is a guy on youTube who talks about the fuses with the handle of Lithium Solar. Check out his videos.
many circuit breakers are not reliable on the DC side of things and are sold by many snake oil salesman as more capable than they are.
i would look at the nec table. 300 amps is a lot and does require a larger cable.
perhaps if you use battery cable also known as welding cable with 105 degree C rating 2/0 will have a 300 amp capacity rating.
you really need to look at a battery cable table or a welding cable table to get the corrrect ampacity rating.
southwire royal excelene 2/0 welding cable is rated at 300 amps for 75 feet.
of course you do not want your inverter cables anywhere this long.
most people try to limit the inverter cable to battery length to 6 feet or less. some say up to 10 feet but the shorter is likely better.
longer cables have more resistance and larger voltage drop.
there is a voltage drop calculator you can get online also. i will see if i can find it again.
2/0 will easily work for 300 amp for you inverter cables. the battery cables or welding cable should be pure copper of a high strand count.
hydraulically crimped ends that bolt onto your fuse or properly sized Dc breaker if you go that route. i large dc breake capable of 300 amps will likely cost 200 dollars or more where as a class t fuse can be bought for 20-30 dollars or less.
https://www.directwire.com/resources/welding-cable-ampacity-chart/#jumptoampacitychart
as an example:
I use 5 feet of 2/0 royal excelene welding cable the voltage drop is 1.13 percent so on a 27.2 volt LiFePO4 battery to inverter the voltage drop thru the 10 feet of cable (5 feet of positive and 5 feet of negative cable) is calculated to be .3536 volts.
therefore the 27.2 volts from the battery to the inverter is decreased by .3536 volts due to resistance and voltage drop 27.2 minus .3536 volts = 26.8464 volts. this is still enough voltage for most all inverters to be able to utilize to output the desired 120 volt AC current.
hope this helps!!!!!! 😎