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. These receptacles are usually found in kitchen wall outlets where two branch circuits are needed to serve small appliances and a refrigerator separately. Switch And Schematic Wiring Diagram To Wire A Duplex Switch And Schematic Wiring Diagram To Wire A Duplex. The wiring diagram on the opposite hand is particularly beneficial to an outside electrician. Sometimes wiring diagram may also refer to the architectural wiring program. The simplest approach to read a home wiring diagram is to begin at the source, or the major power supply.