As a service entrance wire you need AWG # 3/0 gauge copper.
3/0 gauge
Depends upon the voltage. The formula for amperage or (wire size) is Watts / Voltage. If the voltage is 220 volts, then the amperage would be over 400 amps. This would require a large wire size to run it. If it were 440 volts, the amperage would be 1/2 or 200 amps. That would require a smaller wire size. As the voltage goes up, the amperage goes down. At a thousand volts, the amperage would only be 90 amps. A wire gauge or size of a #2 would carry 90 amps for small distances.
To keep costs down, by special permission in the electrical code, for home wiring on a 120/240 volt system 2/0 is allowed. For any other type 200 amp service 3/0 that has a insulation factor of 75 or 90 degrees C is rate at 200 and 225 amps respectively.
6 AWG will handle 50 amps with a voltage drop of about 4 volts. If you go to 4 AWG and limit to 50 amps your voltage drop will be 2.5 volts.
3/0 copper wire with 90 degree insulation is rated at 210 amps. 75 degree insulation is rated at 200 amps.
Service wire required is AWG # 3/0 copper.
3/0 gauge
3/0 wire 3/0 wire
A 3/0 copper conductor with an insulation factor of 75 or 90 degrees C is rated at 200 and 210 amps respectively.
120mm
Depends upon the voltage. The formula for amperage or (wire size) is Watts / Voltage. If the voltage is 220 volts, then the amperage would be over 400 amps. This would require a large wire size to run it. If it were 440 volts, the amperage would be 1/2 or 200 amps. That would require a smaller wire size. As the voltage goes up, the amperage goes down. At a thousand volts, the amperage would only be 90 amps. A wire gauge or size of a #2 would carry 90 amps for small distances.
Each hot leg to the neutral wire of the service has the ampacity of 200 amps, that is why 3/0 wire is required. A 3/0 copper wire with an insulation factor of 90 degrees C is rated at 210 amps.
Actual voltage would be 240V. 4 AWG copper is capable of carrying 50A. At 200 ft, with a 50A load, voltage drop would be about 6V, which is within the acceptable 3% voltage drop for a branch circuit.
For a 125 amp sub panel located less than 200 feet away from a 200 amp panel, you would typically use a 2 AWG copper wire or 1/0 AWG aluminum wire to safely carry the current load. It's important to follow local electrical codes and regulations when selecting the wire size.
To keep costs down, by special permission in the electrical code, for home wiring on a 120/240 volt system 2/0 is allowed. For any other type 200 amp service 3/0 that has a insulation factor of 75 or 90 degrees C is rate at 200 and 225 amps respectively.
A 3/0 copper conductor will limit the voltage drop to 3% or less when supplying 200 amps for 200 feet on a 240 volt system.
To calculate the wire size you would have to find the amperage. I = W/E, 70000/240 = 291.67 amps. The wire size according to code has to be up sized to 125%. 291.67 x 125% = 364.6. 500MCM copper wire with an insulation factor of 75 and 90 degrees C is rated at 380 and 395 amps respectively. If parallel conductors were used the wire size for 75 degree wire would be 3/0 rated at 200 amps. Parallel conductors for 90 degree wire would be 2/0 rated at 185 amps.