Originally Posted by tomkatb
Plugging the inverter just to the shore is the easy method.
But, you need to flip the breaker on the converter. Otherwise it is a battery discharge loop. Simple.
I assume you know to install big wires and a 300 amp breaker or fuse on the wire. Wire should be as short as possible. As big as possible. 4/0. That is 0000.
No argument that large wires are required however the actual size is determined by distance from batteries.
Here's a calculator that makes for easy wire size selection based on Amperage and Distance.
To keep wire size down consider mounting the Inverter as close as practical to the batteries. This reduced the need for HUGE wires. For example, if you can keep the "round trip distance" (total of positive and negative wires) to less than 10 feet you can run 300 amps through 2/0 (00) wire.
If you still want to use smaller wire (often less expensive) you can pair wires for both oisitive and negative conductors. For example, a pair of #2 wires can be more flexible if you have to make tight bends than a singe 2/0 wire.
Many large inverters are built with input lugs that allow for connection to each side with a single bolt.
With a large inverter like described I certainly would mount it as close as I could to my batteries leaving just enough room for air circulation as specified in the manufacturer's installation directions. Running large copper wires any distance gets expensive real quick.
In closing, I used Welding Cable for my inverter installation and battery wiring. Very flexible and not terribly expensive as copper wire goes.