It does not matter how elementary or how challenging a job you plan, from installing a single receptacle to putting in an extensive circuit with several outlets. The number of steps and the order in which they should be done is the same in every type of home.
Jobs tend to go much faster if you follow this logical sequence for putting in new boxes, running cable and connecting the cable to an existing circuit.
Pick out a spot for the new box and break through the ceiling or the wall to make an opening for it. Find the nearest joists or studs and, if the box is to be in a ceiling, find out the direction in which the joists run.
Select an existent box as near to the location of the new box as possible to provide power to the new circuit being installed. The best starting point is a box that enables you to run cable to the new box on a direct route between the floor or ceiling joists, but alternative paths may be needed, depending on such factors as the direction of ceiling joists.
Terminate the power at the service panel and remove the cover plate of the existing box. Check the wiring inside to see if you can connect the new cable wires to the existing wire or terminals. “very Important!” You can not bring power from a box that contains a end-of-the-run switch; and you should not bring power from the box of a light fixture controlled by a wall switch rather than a switch in the fixture itself, otherwise the added wiring will also be controlled by the wall switch.
Count the connections in the box to see if there is room for more cable wires and clamps. If the box is way to small you must gang it to another box, install a deeper box or start the circuit from another place. Check the fuse or circuit breaker at the service panel to be sure that the existing circuit has enough capacity to run all the lights or appliances you may use for the new branch created.
It would be wise to make a map of the room showing the existing box, the new box, the location of the studs and joists, and the path along which you plan to run cable. At the same time, make a list of the materials you will need. Start with a new box or boxes of the right size and shape, and the hardware for installing them.
Get a rough estimate of the amount of cable you will need to reach the new box. Provide an extra 8 inches or so of cable for connections at each box and an extra 20% to allow for the fact that the cable will rarely run perfectly straight. Make sure to use cable thats the correct gauge for the circuit and contains the right number of conductors. Finally, list the type and number of clamps that will be needed to attach the cable to both the old and new boxes.
Now, run the new cable from the existing box to the opening for the new one. This is commonly the most straining part of the job. It may involve cutting access holes in the walls or ceilings, drilling a path for the cable through the beams along the cable’s path and snaking the cable through the walls or ceilings.
Clamp the cable to both the existent box and the new box. Normally, the existent box is permanently installed in a wall or ceiling; therefore, the cable must be attached with an internal clamp. The new box, which has not yet been installed, will accept an internal or external clamp “your choice.”
Install the new box. The process in which you use will depend a lot on the make-up of the wall or ceiling and on whether the box can be mounted directly to a stud or joists.
Connect the wires of the cable to the correct wires or terminals in the existent box(opposite), and then also to the switches, receptacles or light fixures in the new boxes.
Now, to test the new circuit branch. First, clip a continuity tester to the black wire in the box at the end of the run, and touch the probe to the white wire, the bare wire and to the box itself. the tester bulb should not glow in any of these tests. If it does, there is a short circuit in the new branch: check at each new box for an improper connection, frayed insulation or bare wire touching another wire, and make any corrections needed. Then go on to a second set of tests. Have a helper turn on current to the circuit at the service panel and use a voltage tester to check for power in each device on the new circuit. After these tests, turn off the power immediately.
Finally, patch up all the holes you have made in the walls or ceilings. Then turn on the power again. Your new branch is now ready to use and enjoy!!