3/0 gauge
Wire guage is used as a measurement for the ampacity of the wire. # 14 wire is allowed 15 amp to be applied to it. Voltage is governed by the insulation factor of the wire. The three standard insulations are for 300V, 600V and 1000 volts.
140 AMPS
At the service entrance you will need AWG 1/0 gauge.
It depends upon the distance, but typically a short to medium run (0-50 feet) of 12 gauge can carry 20 amps safely. There are charts that list the gauge of wire and the length of runs that can carry amperages safely. For instance, a 12 gauge wire run 150 feet can only carry 15 amps safely instead of 20. The longer the run, you need to drop a gauge as a general rule.
The voltage does not depend on the gauge of the wire, but on the thickness and type of insulation.
the gauge of the wire determines how much amperage a wire can carry the insulation determines how much voltage the wire can handle
This is a voltage drop question. To answer this question a voltage must be stated.
30amps
The gauge (thickness) of the wire along with the material (copper, aluminum, etc) and the length are factors affecting the current capacity, not voltage. The insulator properties, or distance from other conductors will affect the Voltage capability.
The lower gauge number is always a thicker wire which can carry more current.
3/0 gauge
Wire guage is used as a measurement for the ampacity of the wire. # 14 wire is allowed 15 amp to be applied to it. Voltage is governed by the insulation factor of the wire. The three standard insulations are for 300V, 600V and 1000 volts.
The lower the voltage the larger gauge wire you will need to get the same power.
This is a voltage drop question and a voltage needs to be stated.
A short in the turn signal wiring can cause the voltage gauge to fluctuate. A loose ground wire can also cause the gauge to fluctuate.
Wire sizes are governed by the amperage the wire is to carry. To answer this question the load current is required.