Here a switch has been added to control an existing receptacle. The switch takes the hot from the middle receptacles. With this arrangement, all the other receptacles are wired directly to the hot source and the switch controls the middle outlet.
The neutral and ground wires for the circuit are connected to a bar along the side of the service panel box. The neutral and grounding bars in the box may be separate or, in the case of older service panels, the same bar may be used for both purposes.
This page contains wiring diagrams for adding a new light fixture using an existing receptacle as the source. Diagrams include adding a light from a switched receptacle and tapping an always-hot outlet. Different wiring arrangements are included to allow for either the light or the switch to come first in the circuit.
If you’re installing a new doorbell, a remote controlled device makes for the simplest installation and doesn’t require any of the circuitry illustrated on this page. All that’s required is to mount the button near an exterior door and the chimes in a convenient, central location inside the house. No need to run wires or splice into household circuits, fresh batteries are all that’s required.