I am running an electrical line for an a/c unit 220 it calls for 20 amp breaker about 15' underground and the rest overhead in conduit 80' total. My question is what size wire should I use? Thankyou in advance
What size wire for 20 amp 220V 80′
exterior
Related Solutions
According to NEC table 300.5, for using a branch circuit of 120V and not more than 20A, with GFCI protection:
- If it's under 2" thick concrete or equivalent, then depth = 6" and you can use direct burial-rated -- i.e. type UF -- cable, or run in a conduit
- Under a driveway (for 1-2 family homes), depth = 12"
- Under lawns (and anywhere except streets, buildings, parking lots), depth = 12" for direct burial-rated cable, or 6" in a metallic conduit
In general you can use these guidelines.
These are very good guidelines that are widely recognized. However if getting inspected I would just ask your building department for their code requirements.
**NOTE***** This is how deep your footings would be in undisturbed soil. So for example if there was a regrading of the land - as often the case in new builds - you would have to go this deep past the disturbed soil or consult an engineer that would sign off on something else. So if they regraded your land to 3 feet and you lived in Arkansas you would need to go to 54 inches or gets clearance from an engineer to put the footings shallower.
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Best Answer
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