That depends on the voltage of the motor and the circuit. A 40 HP motor is a fairly large motor. If you don't know the answer to your own question, it's unlikely that you're qualified to wire it. Better consult and/or hire a qualified commercial electrician.
The minimum size wire that can be paralleled together stated in the electrical code book is a #3 copper conductor.
This answer is taken from the CEC. Table 17 states minimum size of grounding conductors. For a service conductor drawing 400 amps a #3 copper grounding conductor is needed. Also see rules 10-206, 10-700 and 10-812 if you have access to the code book.
A 100 amp residential service requires a size #8 copper wire, it should be insulated in green.
what size motor
When you talk of voltage, you should be thinking of the insulation factor of the wire. By the same token when you talk of wire size, it is based on the amperage the wire is required to handle.
between 40hp and 125hp
The amount of an electric motor's copper depends upon the size of the motor and the supplies used to make it. Generally, the older the motor, the more copper will be present.
The minimum size wire that can be paralleled together stated in the electrical code book is a #3 copper conductor.
Depends if it fiberglass or Aluminium. For Fiberglass you would be looking at around 50hp-60hp and and Aluminium would be between 30hp and 40hp.
Need motor voltage, amperage and phase to give you an anwer.
Use only AWG # 10 copper.
The wire that is used for connecting the ground rod or plate to the electrical distribution is governed by the size of the electriclal distribution. In Canada a #6 bare copper is the minimum size for a 200 amp service.
A #1 copper conductor with an insulation rating of 90 degrees C is rated at 145 amps.
Number 10 thnn copper wire.
A 2/0 copper conductor with an insulation factor of 90 degrees C is rated at 185 amps. A motor feeder by code has to be 125% greater than the motors full load amperage. Therefore 175 x 125% = 218 amps. A 4/0 copper conductor with an insulation factor of 90 degrees C is rated at 235 amps.
This answer is taken from the CEC. Table 17 states minimum size of grounding conductors. For a service conductor drawing 400 amps a #3 copper grounding conductor is needed. Also see rules 10-206, 10-700 and 10-812 if you have access to the code book.
30 amp breaker with #10 gauge copper wire