What size wire for 20 amp 220V 80'
Why we cannot accurately answer this question

In order for someone to give you an accurate answer to a question such as yours, we need to know at least three things and maybe a forth.

Length or the run - you have

Run load amperage - you don't have

Type of conductor (copper or aluminum) - we are assuming copper

Ambient temperature - we can get back to this one.

Just because the AC you are installing calls for a 20A breaker doesn't mean it needs the entire 20A. 20A breaker is the overcurrent protection device that trips if the circuit is in danger of damage by a short, compressor lock, or some else that goes wrong. It does not indicate the operating amperage of the unit.

Somewhere on the unit there is a nameplate and it should have the RLA (run load amperage) FLA (full load amperage) or just an amperage or maybe even a HP rating. 

So what if I can't find the nameplate rating?

Then rather than just taking a WAG (wild ass guess). We take a SWAG (scientific wild ass guess) and run a calc based on the breaker size, but all guarantees go out the window.


This chart is part of a cookbook I gave to the field so they could do a quick reference in the field without have to run a calc.

So you can see that if we have AC running at a 20A breaker and at a 3% voltage drop we can run a feeder 166' with a number #10 copper conductor. Remember the fourth thing you needed? This chart was developed using 75 degrees C. Since you are running conduit in an exposed environment we would need to know the climate you live in, your compass exposure and how you intend to mount your conduit (distance from wall).

So can we run #12? - Don't know not enough information.

Can we run #10? - Probably safe and since it's only 1/2 the allowable distance, SWAG best option.

Can we run #8? - Super safe depending on how much you are willing to spend.

Would you like to get a tighter answer? We will need to get more information.

Good luck