2nd floor rewiring question


I'm rewiring 3 bedrooms on the second floor of an old (1920s) house. All knob and tube has been disconnected. I've got lighting done, but now doing bedroom general outlet circuits. I'm putting each bedroom on its own 20amp circuit.

The house has plaster walls that are in very good shape, and I want to keep opening up these walls to a minimum. My plan is to make the home runs from the basement to an outlet in each room, through an exterior balloon framed wall. Then, run up to the attic/crawlspace and back down to the next outlet, and so on. Each room has 5-6 outlets, so that means a cable coming down, and another going back up in the same stud bay. I had a couple people advise that this was a good way to do it, including a commercial electrician.

I already roughed in one of the bedrooms this way, but then looking at other examples I saw online, I'm second guessing myself. Many people seem to be cutting a horizontal channel out of the walls to then make horizontal runs between outlets. Another option I came across was one central junction box in the attic for each circuit with wires dropping down to each outlet.

Is there anything wrong with my method (not just from a code perspective)? The extra wire doesn't bother me, I just don't want to make any compromises in safety.

Best Answer

Any of the above are fine. I would not be a fan of the "make a channel horizontally" method because of the destructive factor.

The "star" topology, one large junction box in the ceiling, is ideal because it keeps wiring length the shortest, just panel to box and box to receptacle. It is also the easiest if down the road you want to increase power capacity in there to run portable heaters, gaming PC, what have you.

The box needs to be large. You will need 4.5 cubic inches, plus another 4.5 cubic inches for each cable coming into it including supply. My go-to is a 4-11/16" steel box, which has 42 c.i. good for 8 cables. A proper electrical supply will have them for $2-something, expect to overpay at a big-box store, which is ironic since you'd think they'd specialize in, well, big boxes.

However, the attic junction box must remain accessible. It can't be "improved over" or if you do, you have to put a hatch there to allow access without disassembling any part of the building. Also don't bury the box in insulation, it needs air contact to carry away any internal heat.