When planning new electrical service, begin by deciding where you can tap into power. If you are adding a couple of receptacles or lights, it is usually easiest to grab power from a nearby receptacle or junction box. First, however, make sure the new service doesn't overload the circuit.
If nearby boxes are on circuits that do not have enough available wattage for the new service, try a box farther away. If no circuit is usable or if the new service needs its own circuit, run cable all the way to the service panel and connect to a new circuit breaker.
If you need to, run cable through walls and ceilings to get at power.
About 2 hours to connect new cable to an existing receptacle or junction box (not including cutting a pathway for the cable and patching walls)
Voltage tester, drill, pry bar, saw, close-work hacksaw or reciprocating saw, hammer, screwdriver, strippers, long-nose pliers, lineman's pliers
Stripping wire and connecting wire to terminals, running cable through walls, prying and cutting nails
Spread a drop cloth or towel on the floor. Run cable to the box from which you grab power.
New cable, wire nuts, electrician's tape, cable clamps, remodel box
If two cables enter the box, the receptacle is in the middle of a run. Splice the wires and connect to terminals with pigtails as shown. The purpose of pigtails is to avoid multiple connections to one terminal screw where they could easily short or come loose. Make pigtails by removing the sheathing from about 8 inches of NM cable. Strip about 3/4 inch for each end of the black and white wires and attach them as shown.