How to add Romex Cable to this Junction Box

Hi Gabriel,

There should be several round indentations on the box. These are knock outs and can be removed by hitting them with the tip of the screwdriver. An adapter that screws into the resulting hole can be purchased from a hardware store. Make sure you get the correct size. Here in the US I think the 1/2 inch is the most popular but it must be matched to the size of your knock out. The steel sheathed cable should also be available at the hardware. Be certain to get an adapter that will not only fit into your knock out hole but will also attach to the romex. Once you are inside the junction box you will also have to ID the hot and the neutral wires. Usually the hot is black and the white is neutral. This can sometimes be confused if there are switched lines coming from wall switches to ceiling lights in the box. A small fluke field proximity tester can be very useful to determine this. Junction boxes in the ceiling frequently have only switched hot lines in them. This means that unless the switch that turns on the ceiling light is on you will not have power in the black wire. I do not know your situation but be safe and good luck.

John

Thank you for the help.  I am having trouble identifying the necessary adapter and steel sheethed cable.  Do you think you could give me a name/keywords to search or just link me to one that would work?

Hi Gabriel,

I did not look at your video until after I posted so now I believe that you should use the 12/3 or 14/3 romex and enter the box using this type of adapter clamp. Forget about the steel sheathed wire I mentioned.

https://www.amazon.com/Romex%C2%AE-Connector-1-2-in/dp/B0003S2MEQ

You will still have to make sure the size matches the holes in the box. I also think it would be a good idea to locate the power wires before you do any removal of knockouts or other installation. The outlet box on the other end of the line can be a plastic box in most residential areas. Based on the picture I am assuming that it is a single family residential building. Make sure that your wiring is staple down and secure as this type of wire does not tolerate being move around like an extension cord does. The solid wires can break off if bent too much or pull loose from connection points. The Fluke hot wire tester I mentioned is still a good idea and will allow you to tell if a wire is hot or not just by putting the tester near the wire.

https://www.amazon.com/s/ref=nb_sb_ss_i_1_13?url=search-alias%3Dtools&field-keywords=fluke+voltage+detector&sprefix=Fluke+voltage%2Ctools%2C179&crid=1LRHQG086IBPB

I hope this helps.

John

The steel cable is called BX and you can buy it in rolls at Home Depot, but you should stick with 14/2 w/ground NM-B cable(romex).

Here are some good instructions to follow

https://www.handymanhowto.com/how-to-wire-an-attic-electrical-outlet-and-light-part-2/

"for a bit of extra safety, wear rubber gloves and keep 1 hand behind my back."  AND whistle Dixie while you work lol!

Dennis and John have some good advice:  I should of let things be, but I wrote this so I am gona post it anywhere, as long winded as it is!

Holy sparks, Gabriel: You should have a meter to measure 120 / 240 volts AC.  You need to take off the cover, loosen one screw and remove the other.  You will see the wires connected together with wire nuts.  Hopefully there are 3 white (neutral) and 3 black (hot) wires, and 3 ground wires, each connected together with their own wire nuts.  (If not, OR if you see a red wire, STOP and study, there may be a switch or something.  You are looking for a simple 120 Volt AC circuit, right?)  If you are lucky, the older metal BX cable may be an original feed (already with lots if stuff on it?) from an existing circuit, originating from the service panel.  The two romex cables were run at some later time feeding lighting or receptacles?  Follow the wires, especially the "Newer" romex, down where they protrude into the wall below and do your best guess on where they go. Lights? Switches? Outlets?  If one wire looks like it goes to a switch, it disconnects the HOT (black) wire going to a light, so be aware.  Do some good reasoning. Read about residential wiring  Once your have a best guess, you should then go down and identify the breaker that controls THAT circuit somehow.  Sometimes the breakers are MARKED within the service panel, making it obvious. 

The Breaker MUST normally correspond to the gauge of the wire you have to use:  14 gauge for 15 amp circuits, and 12 gauge wire for 20 amp circuits.  The Romex wire you use must be the minimal gauge.  You need 14-2 with ground, or 12-2 with ground, having a black and a white conductor, and a bare copper ground.   NOT 12-3 or 14-3!   Also check the existing romex wire markings, they should say 14- 2 or 12-2 with ground, and correspond with the breaker feeding the circuit.  Be aware that the person adding the new circuits may of not been an electrician, and wanted to use the "cheaper" 14-2 with ground on a 20 amp circuit which is illegal and dangerous.  That'ts why we are ELECTRICIANS!

Again, Gabe:  You need to be sure your dealing with 120 volts AC, uses your meter to test between a white wire and the black wire.  You would use ROMEX or equivalent wire, of the proper gauge.   They call the stupid clamps  that hold the wires to the box "connectors" for some reason, there are plastic ones and metal ones made for 1 or 2 romex cables.

DON't turn off the MAIN BREAKER, gosh, Gabe!

WITH THE CIRCUIT BREAKER OFF:  You add another wire to that 4" square junction box.  You may even be able to use the existing wire nuts, or use larger wire nuts inside to accommodate the larger number of wires.  Locate and tap out a small knockout the same size used for the romex, remove the sheathing from the romex about 6", and take about 5/8 inch of insulation off the black and white wires.  Connect the black to black (hot) and the white to white (Neutral) using wire nuts .   Connect all the bare copper ground wires together with a wire nut.  Hopefully you see the metal box also has a bare copper ground wire included with the bunch.

Receptacles have the same arrangement.  Decide how you want to attach a single or double receptacle box to the floor, wall, ceiling, rafter, and select a box that mounts that way.  Some plastic boxes have built in clamps, and some metal boxes do to, but if not, you will have to have clamps (oh, yah, "connectors")  On the recepticles, the silver colored screws are for the white wire, the brass colored screws are for the black (hot) wire, and the green screw is for the copper wire.  Get a face plate for your box.

Go to Home Depot if you have that around, or your local home supply store, and dig around.  Read. Watch YouTubes.  Do it Right.

Gabe:  Electricians make LOTS of MONEY and get very dirty doing it.  It beats living in the basement 'till you're 32.

Pete, N2EXG

Thanks for the very in depth description.  I just went up and opened the 4" square junction box, but the wires aren't connected to the same color.  I see black to white and red to black and there is a blue wire.  There is are two metal tubes with wires feeding into it and 1 romex feeding out of it.  What should i be looking for?