This is a voltage drop question and a voltage needs to be stated.
#6 wire stranded
AWG-8 wire can safely carry 30 amps to a load 100 feet away.
AWG # 6 copper
Use 2/0 AWG.
2 AWG in Aluminium is required.
A #2 copper wire with an insulation factor of 75 and 90 degrees C is rated at 115 and 120 amps respectively.
A #6 copper wire with an insulation factor of 75 or 90 degree C is rated at 65 amps.
Yes, a #10 wire will carry 30 amps for 30 feet. If the load is rated as continuous then the wire will have to be derated to 80% capacity which will leave you with 24 workable amps. If the load demands currents higher that 24 amps then you will have to go to the next wire size up which is a #8 which is rated at 45 amps.
10 amps is the maximum it will carry.
A # 14 copper conductor will be fine to carry 8 amps at 120 volts. This size conductor is rated at 15 amps.