I want to know if this is the correct way to do this.
There is a switch that controls a single receptacle in a double receptacle outlet across the room. Power comes into the switch box via 3-wire (black/white/ground). There is a 4-wire (black/white/red/ground) going to the switch via the attic. The whites and grounds are nutted together respectively. The blacks are also nutted together and pigtailed to the black screw on the switch. The red is connected to the other side of the switch. Over at the outlet, the red wire is connected to the top (switched) receptacle, and the black to the bottom (and the white is connected to both of course and it is grounded).
I want to install a ceiling fan with a light fixture on separate switches. The switch is on an interior wall but the outlet is on an exterior wall. The 4-wire passes right overhead (in the attic) of where I the ceiling fan will mount. What I want to do is cut the 4-wire near where the fan will go, route the 4-wire into the fan box, and replace the single switch with two switches that switch the black AND red wires that now go to the fan and light. Then, run a new 3-wire up from the switch box, with has constant power, to a new junction box and jumper the new 3-wire to the old 4-wire, leaving the red unconnected. Then, I will replace the outlet such that both receptacles are powered from the black only and leave the red disconnected.
Being an electrical engineer, I know that this will work from a power-distribution standpoint, but are there code violations or better ways to do this?
Best Answer
Yes, this should work. A few things you may have already considered:
Each time your cable goes into or out of a junction box you should plan to lose 6" in length.
So tying into and out of the ceiling box for the fan would require 12" of slack on the existing 4-wire cable. Your plan to add a separate junction box is a better approach. The trick is to put it at least 6" closer to the dual-wired receptacle and run 3-wire the longer distance to this box. When you tie into the 4-wire here you will have extra 4-wire to use in the ceiling fan box.
Don't disconnect the red wire going to the duplex receptacle.
Just tie red and black to the un-switched black in your junction box. This puts half the load on each wire and you don't have to rewire the receptacle in the wall.
Get a deep 2-gang switch box to fit all those connectors
and dissipate the heat any dimmers you use to control fan speed or dim the fan lights. You're looking at needing at more than 29 cubic inches not counting extra for dimmers. And you always want to leave room for future expansion.
Get a ceiling box designed to hold a fan and mount it securely to a joist.