Electrical – Running romex in 20″ attic space using pipe hangers

atticelectricalinsulation

My drywall ceiling is attached to 2×6 joists 16" OC. Then, a 10" air gap above these joists are the 2×6 rafters 32" OC, for my flat roof just above. Even though the home is 1955, I have knob & tube throughout this attic space which I'd like to replace. Also, I'd like to improve the current insulation which is blown-in cellulose only about 4" deep (you can see the ceiling joists if I pop my head up).

I'm thinking of installing some 3" pipe hangers such as below, on the underside of the rafters, to help with running 12/2 NM-B romex cables for now and in the future. I'd put one above the light fixture and one near the attic access hatch (for each room).
3-inch tube strap

QUESTIONS:

  • Is there a better/standard option rather than these pipe hangers to
    accomplish my goal?
  • Am I overthinking this and I should just let the romex be buried
    by the new/additional blown-in insulation?

Pic of my "attic"
attic

Footnote: The new wire which replaces the k&t will be run from the basement below, where the main panel is, and only switch-to-light wires will be in the attic. And I'll leave the old k&t in place, but disconnected.

Footnote 2: I'm very tempted to completely rip off the ceiling drywall and do batt insulation or spray foam, but I fear the cost/time will be prohibitive.

Best Answer

If you want future-proof, run conduit

You simply need to comply with conduit rules, which can be a bit tricky since it's not normal to run cables through conduit.

  • Four cables (circuits) per conduit, no more.
  • It's a pain to pull it through. Individual THHN wires are much easier, but you're not allowed to unjacket cable to run it through conduit. (the inner wires aren't rated for it/tough enough).
  • Very large conduit. When running cable through conduit, it counts the same as a wire of the larger (wider) dimension, i.e. 0.4" diameter for #12-2 NM-B. So something like 1-1/4" conduit should be good for most stuff (two or more #10s might exceed it, as might wide, narrow UF).

If you need the gory details, look at the width (wider dimension) of the cable (wireandcableyourway.com has that detail), and punch that into a conduit fill calculator, as a "custom wire size". For "number of wires", put the number of cables.

If you don't do conduit all the way from panel to destination, then you are simply using conduit as a cable protection method. That is fine, but it isn't technically "wiring in conduit". That means for instance you can't use THHN individual wires.

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