They are not interchangeable. Look at the face of the outlet and notice how one of the openings in the socket is narrower than the other. The narrow slot is for the "hot" lead, usually, but not always black. It usually connects to a brass-colored screw on the back or side of the outlet. The wider of the pair is the "neutral", and it is usually a white wire that attaches to a silver-colored screw. The bare wire goes to the green screw and is called "ground". That is the one that prevents you from getting fried if a white wire comes loose. The bare wire may be replaced by the armored conduit depending on where you live, and if the other end of the conduit is properly grounded.
I am no expert, and I mean no disrespect, but there are lots of books out there at libraries and home centers that explain the basics of residential wiring. If you make a mistake and smoke some low-voltage item like your Elk, you'll be really upset. If you make a mistake on the high voltage stuff, you won't care nearly as much as your survivors. This is serious stuff. It can kill someone. Maybe you should take a break and check out the library before you get too far along on the outlets. Especially the outdoor outlets where it gets wet.
Best wishes. . . . John