How to Wire a 120-Volt Wall Outlet | Home Guides | SF Gate Turn off the breaker that supplies power to the outlet you'll be changing. If you do not know which Test the wall outlet for power with a voltage tester. These are available at hardware stores. They Remove the cover plate on the outlet to be wired. In most cases you will need a small slotted-head Test the wires on the sides of the wall outlet. This is a precautionary test in case the socket is See all full list on homeguideste Wiring Diagrams for Electrical Receptacle Outlets - Do-it Wiring Diagram for a 20-Amp 120-Volt Duplex Receptacle. A 20 amp, 120v duplex receptacle outlet like this should be installed in a circuit using 12 awg cable and a 20 amp circuit breaker.