I would run up to the attic, over, and down. Unless you have basement access, it's the only way you'll do this without cutting up the wall. (I also value the absence of cords across my walls.)
- Carefully disconnect all wires in one box, removing the outlet and all nuts. Take photos or make notes if you think you'll need them later.
- Depending on the box type, remove it by cutting the nails with a small saw. A hacksaw blade in a Vice Grip plier can be useful. If it's a brown fiber box you can break it up with a plier. Remove the box from the wall completely while taking care to not damage your drywall. A couple layers of painter's tape around the opening are a good idea.
- From the attic, drill through the double top plate in the same stud bay as the box.
- Drop a new 12/2 cable down to the box opening, ideally in front of the insulation but behind the vapor barrier. An assistant is helpful here.
- Cut a new hole behind your tv, sized for a remodeler (old work) box. Double check stud locations first. You don't want to have to notch a stud. If you mess up there, a sharp 1" spade bit will make quick work of the stud. Be sure to consider your tv mount location as well.
- Drill through the top plates in that stud bay as well, and drop other end of the cable down.
- Install remodeler boxes at both locations and install the outlets. Be sure to use a deeper box at the original location as it'll have many connections.
Be prepared to do some sweating and swearing, but for the aesthetically-minded homeowner it's worth it to have completely clean walls around a hanging tv panel.
This must be a 15A or 20A circuit. If it is 25A or larger, you are not allowed to put the usual receptacles on it.
That funny thing is a conduit body. It's made to ease pulling. You cannot splice there.
First, pull the wires out of there. Find the ends of the wires (i.e. at the service panel or at the next junction box where they splice) whichever is closer. Unsplice them and pull them back, all the way to the conduit body and a little past. That way you don't have to cut the wires.
Then replace the conduit body with something else. You can change it to a "Tee" conduit body, or to a junction box. A junction box is a great deal more useful. You'll need to work in the same kind of system you're already in, e.g. if PVC conduit, then either use PVC boxes, or use PVC threaded ends to go into any other kind of box.
Next, extend the conduit pipe system to your new receptacle.
Now put the original wires back and you're back up. Now figure out how to add the additional wires. Now let's review the rules:
- You cannot make any splice in a conduit body, only junction boxes.
- Each wire must have 6" from where it enters the box, and also stick out of the front of the box at least 3". At both ends.
So if you added a conduit body "tee" you'll need to run wires from the new receptacle, through the "tee" to a junction box where you can splice. Watch out that you don't overstuff your conduit, the legal max is 9-12 wires depending on several factors.
If you added a new junction box and want to make the splice there, you'll have to see if they left you enough slack for the required lengths in all locations. If not, you'll have to sacrifice one side or the other, and replace them with longer wires. Take them into the electrical supply and ask for wires 2 feet longer. They can help you match up the size and type. Also get the new wires (same size and type) you'll need for your new branch, if you're branching.
If you know you'll have to sacrifice wire, you can save time at step 1 by doing that first.
You drew it with "wire nuts" or some other kind of splice tying all the wires, and a short pigtail to the receptacle. That is correct. You must pigtail the ground, always. You must pigtail the neutral because this is a multi-wire branch circuit (which have many complicated rules). You aren't required to pigtail the hot, but it can help especially if it's in a cramped location. (you can attach the pigtails to the receptacle at your desk.)
Best Answer
What you did is just fine. That is what any experienced electrician would have done.
If all of the wire in the entire circuit is #12 you could change your breaker to a 20 amp breaker for more capacity. If any of it is #14 you have to stick with the 15 amp breaker.
The previous setup is a waste of wire. They could have put one junction box in the middle of the room and dropped to each box OR they could have hit one box and then daisy chain to the other three boxes through the studs if the room only had one door.
There are many ways to get the job done and sometimes it is just a personal preference.
Your setup is fine though. Good luck!