what is the formula for figuring electrical wire size based on 200amp ac circuit the wire must be 70 ft long?

Answer 1

The answer is already in the question. Use the National Electric Code to determine the conductor size for 200 amps depending on application. 4/0 aluminum conductor will handle 200 amps at 70 feet with ease. It is the standard service entrance size cable required by most electric utilities to supply a 200 amp meter base.

Answer 2

If the wire is in a conduit, use 3/0 (although I would probably shade it a bit and use 2/0). If it is in open air, 1 gauge is sufficient for THHN.

Answer 3

Pick up the phone and check with your local city and county building code requirements.