This circuit diagram shows the wiring for a new receptacle outlet connected at a light fixture. The source at the fixture is always hot and a switch loop controls the light. New 2-wire cable runs from the fixture box to the new receptacle and the source hot, neutral, and ground are splice to it along with a pigtail back to the fixture circuit. With this arrangement the new receptacle is always hot.
This is an updated diagram for the same circuit. Here the source neutral, known as a grounded neutral, is run through to the switch box where it can be used to power switches that require a neutral connection. A neutral connection like this is now required in most new switch boxes as of the code changes in 2011.
This diagram illustrates the arrangement for a 20 amp double receptacle circuit with a shared neutral wire. This arrangement is typically used in a kitchen where two appliance circuits are needed in close proximity to each other.
New 2-wire cable is run from the receptacle to the new light fixture. At the receptacle the wires are removed and each one is spliced to the new cable and back to the receptacle with a pigtail splice. At the light fixture box the black wire connects to the hot terminal, the white connects to the neutral terminal and the ground to any metal grounding terminal on the fixture, outlet box, or both.