Re: Tri-Metric Tm-2025-Rv install
The shunt essentially "breaks" the negative wire. Battery wire, shunt, wiring to the inverter, charge controller etc.
The size of the wire, (any wire) needs to be able to carry the expected current. Remember, an inverter suppling 120vac loads at any given amperage, that same load at the battery at 12 vdc will be 10 times greater. A 300 watt load at 120 vac will draw 2.5 amps, but will draw 25 amps from the battery. (Plus inverter loses!)
Additionally, the wire size needs to carry the load, but you have to consider line loss. Lower voltage means more line loss per foot. When in doubt, use the biggest wire you can.
#8 wire will carry ~ 40 amps,, #2 will carry ~ 90 amps. 40 amps @ 12 vdc is ~360 watts.
#4 will carry 70 amps or ~ 840 watts.
So it all depends on what you are planning on powering with your inverter. Also consider how much charge current you are likely to have.
Please note, being a moderator does not add any weight to my opinions 300 watts Siemens/BP panels,plus a Sun 90,, making ~400. ~30 amps into Rogue MPT-3024, 450 ah of Trojan T-105, Morningstar ts300 inverter, a Tri-Metric meter.a collection of antique generators, plus 2 Honda eu-1000i's (also a BS2512 IX controller) and assorted other stuff!