Hello, I will be running 14/2 wire with ground to run a wall a/c unit. The a/c unit pulls about 12.5 amps. Question is some part of the wire will be run outside under a deck. About 15 feet. This part I obviously will have to protect with conduit but is it really necessary for me to have to use exterior grade wire which is usually made exterior grade because it will be run underground. The wire should be shielded from the sun and the elements because of the conduit but it might still be necessary with all I know. I think they call interior grade nm-b. Thanks:cool:

First #14 is too small for a AC unit drawing 12.5 amps, the wire size needs to be rated 125% of the running amps, 12.5*125%=15.6 amps, so need #12 wire. This should be on a 20 amp breaker.

If you can get the conduit to exit the building at one end and enter at the other, then using it as a continuous sleeve for the NM-B cable is fine, good thought , will help to eliminate splices.

You may want to consider using 3/4 conduit, the cable will fit much better, and the 90 deg fittings are larger.