Your transceiver's user guide suggests limiting the voltage drop to 0.5 volts and the vehicle battery is 3 metres away. Given the losses listed below at the required current of 22 amperes, which minimum wire gauge must you use?

To calculate the total voltage drop, you must account for the entire round-trip length of the circuit. Because the battery is 3 metres away, the current must travel 3 metres along the positive wire and return 3 metres along the negative wire, resulting in a total wire length of 6 metres. Next, multiply the total length by the voltage drop per metre for each wire gauge. For Number 10 wire at 0.07 volts per metre, the total drop is 6 metres × 0.07 V/m = 0.42 volts. Since 0.42 volts is safely below the maximum allowed drop of 0.5 volts, Number 10 wire is the minimum acceptable gauge. If you used the thinner Number 12 wire, the drop would be 6 metres × 0.11 V/m = 0.66 volts, which exceeds the limit.