Cable sizing is determined by the size of your inverter. National Electric Code standards are strongly suggested when wiring a system. Recommended sizing is as follows; #4 gauge is not to exceed 157 amps DC (approximately 1500 watts), 1/0 is not to exceed 291 amps (approximately 3500 watts), and 4/0 is not to exceed 454 amps (approximately 5000 watts.) These ratings are based on a 12-volt system.