I guess I should have written it as, the higher the voltage the smaller the wire can be.
The wire running to my street is 30,000 volts and the transformer steps it down to 220 volts single phase. Is the wire for the 30,000 volt line bigger ? Not by much if any. If I was lucky enough to be in a industry street than I could get 3 phase, because the current is less on each leg the wire can be smaller. A 6 volt DC starter will draw twice as much current vs a 12 volt DC starter motor so the 12 volt motor needs a smaller wire than the 6 volt.
500 Watt starter motor
500W/12V = 41.7 Amps
500W/6V = 83.33 amps
6 Volt starter motor needs a bigger wire.
