A #8 copper wire with an insulation factor of 75 or 90 degrees C is rated at 45 amps.
That would depend upon how many amps will be used in the sub-panel. For example, a 30-A subpanel would need a minimum of 10 AWG feeder conductors.
140 AMPS
3/0 gauge
Yes, # 4 AWG copper and 100 amps is the max.
Typically 30 amps.
50 amps
The amps that a four gauge wire will handle will depend with the thickness of the wire. If the wire is thin, the four gauge will handle 95 amps.
That would depend upon how many amps will be used in the sub-panel. For example, a 30-A subpanel would need a minimum of 10 AWG feeder conductors.
140 AMPS
15 amps
70 amps.
180 amps. Assuming the panel will be loaded only 80%.
3/0 gauge
50 amps
You should never try to use more than 15 amps through a 14 gauge wire.
#10
Yes, # 4 AWG copper and 100 amps is the max.