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My drywall ceiling is attached to 2x6 joists 16" OC. Then, a 10" air gap above these joists are the 2x6 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.

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    These pipe hangers are neither designed for nor listed for hanging house wires. You can have no assurance that they would not cause actual problems, but even if they didn't, you would have an installation that could be questioned. – Jim Stewart Apr 29 at 10:34
  • I fully agree with Jim, get a box of staples, if you are only putting in 1 circuit get a box of standard length staples, if putting in 2 get staples listed for 2 cables, more run them parallel or purchase stackers, I use long staples and 2 cables together all the time. + Jim – Ed Beal Apr 29 at 18:32
  • At the very least use plastic hangers without serrated edges. :O – isherwood Apr 29 at 19:59
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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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As mentioned in a comment, those are not listed to be used for electrical cables. If you are just running one cable in one run, just use regular NM cable staples like these:

Cable Staple

If you are running multiple cables and would like to save some time, you can use "stackers" like these:

Cable Stacker

If you added another 2x4 to the side of the members that run perpendicular to your joists, you could also just use that as a raceway and run your cables in there.

Edit: To answer the second part of your question, it will be fine for the cables to be in the blow-in insulation. If you think you will be doing lots of work up there and changing things around later, you might to have the cable up higher so you can find them easier later. But that is personal preference.

You may also want to look at this question, it goes over the requirements for additional protection if the cables are in an accessible attic (vs one without access).

  • I'm using staples for the romex in the basement and could certainly do that for my attic situation, but I was trying to think of something more future proof. My other idea was to install open-ended conduit on underside of rafters, that I could run the romex through. Future maintainability is not a requirement, just trying to think ahead. – dabi Apr 29 at 18:29
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I'd go with a "stacker" or "tree" style of NM holder

If I was trying to provision for the future in your situation, but a full conduit system (vs. cables in conduit) was out of the question, then I would use a "stacker" or "tree" style of NM holder that nails to the bottom of the joist and spaces the cables apart in its clips, such as the Bridgeport NMWH-43 depicted below.

a Bridgeport NMWH-43

(P.S. a short space under a flat roof, like yours, is called a cockloft much of the time)

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