In this diagram, two receptacle outlets are wired in the same box with a separate 120 volt source feeding each. Three-wire cable runs into the box. The black and red wires are hot and each is connected to one of the receptacles. The white, neutral wire is splice to each outlet so they share the return path. This is appropriate for standard duplex receptacles, but should not be used for GFCI receptacles. GFCI’s must have dedicated neutral connections to work properly.
In this arrangement a light fixture and exhaust fan are wired to the same source. The light is controlled with a single-pole switch and the fan controlled with a timer as in the previous drawing. The hot source is spliced to each controlling device and the output of the controllers are connected as in the previous diagrams on this page.
Here 3-wire cable is run from a double-pole circuit breaker and split to supply 120 volts to two sets of receptacles. The neutral wire from the circuit is shared by both. This wiring is commonly used in a 20amp kitchen circuit where two appliance feeds are needed, such as for a refrigerator and a microwave in the same location.
Use this wiring when the source is at the fixture and you want to control the feed to both components with the same switch. Three-wire cable runs from the fan to the switch box and the source neutral is spliced to the white wire and to the fan neutral.